GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools

Problem, Formatting or Query -  Send Feedback

Was this page helpful?-10+1


rfc:rfc3525

Network Working Group C. Groves Request for Comments: 3525 M. Pantaleo Obsoletes: 3015 LM Ericsson Category: Standards Track T. Anderson

                                                            Consultant
                                                             T. Taylor
                                                       Nortel Networks
                                                               Editors
                                                             June 2003
                Gateway Control Protocol Version 1

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

 This document defines the protocol used between elements of a
 physically decomposed multimedia gateway, i.e., a Media Gateway and a
 Media Gateway Controller.  The protocol presented in this document
 meets the requirements for a media gateway control protocol as
 presented in RFC 2805.
 This document replaces RFC 3015.  It is the result of continued
 cooperation between the IETF Megaco Working Group and ITU-T Study
 Group 16.  It incorporates the original text of RFC 3015, modified by
 corrections and clarifications discussed on the Megaco
 E-mail list and incorporated into the Study Group 16 Implementor's
 Guide for Recommendation H.248.  The present version of this document
 underwent  ITU-T Last Call as Recommendation H.248 Amendment 1.
 Because of ITU-T renumbering, it was published by the ITU-T as
 Recommendation H.248.1 (03/2002), Gateway Control Protocol Version 1.
 Users of this specification are advised to consult the H.248 Sub-
 series Implementors' Guide at http://www.itu.int/itudoc/itu-
 t/com16/implgd for additional corrections and clarifications.

Groves, et al. Standards Track [Page 1] RFC 3525 Gateway Control Protocol June 2003

Conventions used in this document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].

Table of Contents

 1 Scope.........................................................5
   1.1 Changes From RFC 3015.....................................5
   1.2 Differences From ITU-T Recommendation H.248.1 (03/2002)...5
 2 References....................................................6
   2.1 Normative references......................................6
   2.2 Informative references....................................9
 3 Definitions..................................................10
 4 Abbreviations................................................11
 5 Conventions..................................................12
 6 Connection model.............................................13
   6.1 Contexts.................................................16
   6.2 Terminations.............................................17
     6.2.1 Termination dynamics.................................21
     6.2.2 TerminationIDs.......................................21
     6.2.3 Packages.............................................22
     6.2.4 Termination properties and descriptors...............23
     6.2.5 Root Termination.....................................25
 7 Commands.....................................................26
   7.1 Descriptors..............................................27
     7.1.1 Specifying parameters................................27
     7.1.2 Modem descriptor.....................................28
     7.1.3 Multiplex descriptor.................................28
     7.1.4 Media descriptor.....................................29
     7.1.5 TerminationState descriptor..........................29
     7.1.6 Stream descriptor....................................30
     7.1.7 LocalControl descriptor..............................31
     7.1.8 Local and Remote descriptors.........................32
     7.1.9 Events descriptor....................................35
     7.1.10 EventBuffer descriptor..............................38
     7.1.11 Signals descriptor..................................38
     7.1.12 Audit descriptor....................................40
     7.1.13 ServiceChange descriptor............................41
     7.1.14 DigitMap descriptor.................................41
     7.1.15 Statistics descriptor...............................46
     7.1.16 Packages descriptor.................................47
     7.1.17 ObservedEvents descriptor...........................47
     7.1.18 Topology descriptor.................................47
     7.1.19 Error Descriptor....................................50
   7.2 Command Application Programming Interface................50
     7.2.1 Add..................................................51

Groves, et al. Standards Track [Page 2] RFC 3525 Gateway Control Protocol June 2003

     7.2.2 Modify...............................................52
     7.2.3 Subtract.............................................53
     7.2.4 Move.................................................55
     7.2.5 AuditValue...........................................56
     7.2.6 AuditCapabilities....................................59
     7.2.7 Notify...............................................60
     7.2.8 ServiceChange........................................61
     7.2.9 Manipulating and Auditing Context Attributes.........65
     7.2.10 Generic Command Syntax..............................66
   7.3 Command Error Codes......................................66
 8 Transactions.................................................66
   8.1 Common parameters........................................68
     8.1.1 Transaction Identifiers..............................68
     8.1.2 Context Identifiers..................................68
   8.2 Transaction Application Programming Interface............69
     8.2.1 TransactionRequest...................................69
     8.2.2 TransactionReply.....................................69
     8.2.3 TransactionPending...................................71
   8.3 Messages.................................................72
 9 Transport....................................................72
   9.1 Ordering of Commands.....................................73
   9.2 Protection against Restart Avalanche.....................74
 10 Security Considerations.....................................75
   10.1 Protection of Protocol Connections......................75
   10.2 Interim AH scheme.......................................76
   10.3 Protection of Media Connections.........................77
 11 MG-MGC Control Interface....................................78
   11.1 Multiple Virtual MGs....................................78
   11.2 Cold start..............................................79
   11.3 Negotiation of protocol version.........................79
   11.4 Failure of a MG.........................................80
   11.5 Failure of an MGC.......................................81
 12 Package definition..........................................82
   12.1 Guidelines for defining packages........................82
     12.1.1 Package.............................................83
     12.1.2 Properties..........................................84
     12.1.3 Events..............................................85
     12.1.4 Signals.............................................85
     12.1.5 Statistics..........................................86
     12.1.6 Procedures..........................................86
   12.2 Guidelines to defining Parameters to Events and Signals.86
   12.3 Lists...................................................87
   12.4 Identifiers.............................................87
   12.5 Package registration....................................88
 13 IANA Considerations.........................................88
   13.1 Packages................................................88
   13.2 Error codes.............................................89
   13.3 ServiceChange reasons...................................89

Groves, et al. Standards Track [Page 3] RFC 3525 Gateway Control Protocol June 2003

 ANNEX A  Binary encoding of the protocol.......................90
   A.1 Coding of wildcards......................................90
   A.2 ASN.1 syntax specification...............................92
   A.3 Digit maps and path names...............................111
 ANNEX B Text encoding of the protocol.........................113
   B.1 Coding of wildcards.....................................113
   B.2 ABNF specification......................................113
   B.3 Hexadecimal octet coding................................127
   B.4 Hexadecimal octet sequence..............................127
 ANNEX C Tags for media stream properties......................128
   C.1 General media attributes................................128
   C.2 Mux properties..........................................130
   C.3 General bearer properties...............................130
   C.4 General ATM properties..................................130
   C.5 Frame Relay.............................................134
   C.6 IP......................................................134
   C.7 ATM AAL2................................................134
   C.8 ATM AAL1................................................136
   C.9 Bearer capabilities.....................................137
   C.10 AAL5 properties........................................147
   C.11 SDP equivalents........................................148
   C.12 H.245..................................................149
 ANNEX D Transport over IP.....................................150
   D.1 Transport over IP/UDP using Application Level Framing ..150
     D.1.1 Providing At-Most-Once functionality................150
     D.1.2 Transaction identifiers and three-way handshake.....151
     D.1.3 Computing retransmission timers.....................152
     D.1.4 Provisional responses...............................153
     D.1.5 Repeating Requests, Responses and Acknowledgements..153
   D.2 Using TCP...............................................155
     D.2.1 Providing the At-Most-Once functionality............155
     D.2.2 Transaction identifiers and three-way handshake.....155
     D.2.3 Computing retransmission timers.....................156
     D.2.4 Provisional responses...............................156
     D.2.5 Ordering of commands................................156
 ANNEX E  Basic packages.......................................157
   E.1 Generic.................................................157
   E.2 Base Root Package.......................................159
   E.3 Tone Generator Package..................................161
   E.4 Tone Detection Package..................................163
   E.5 Basic DTMF Generator Package............................166
   E.6 DTMF detection Package..................................167
   E.7 Call Progress Tones Generator Package...................169
   E.8 Call Progress Tones Detection Package...................171
   E.9 Analog Line Supervision Package.........................172
   E.10 Basic Continuity Package...............................175
   E.11 Network Package........................................178
   E.12 RTP Package............................................180

Groves, et al. Standards Track [Page 4] RFC 3525 Gateway Control Protocol June 2003

   E.13 TDM Circuit Package....................................182
 APPENDIX I EXAMPLE CALL FLOWS (INFORMATIVE)...................184
   A.1 Residential Gateway to Residential Gateway Call.........184
     A.1.1 Programming Residential GW Analog Line Terminations
           for Idle Behavior...................................184
     A.1.2 Collecting Originator Digits and Initiating
           Termination.........................................186
 APPENDIX II  Changes From RFC 3015............................195
 Intellectual Property Rights..................................210
 Acknowledgments...............................................211
 Authors' Addresses............................................212
 Full Copyright Statement......................................213

1 Scope

 The present document, which is identical to the published version of
 ITU-T Recommendation H.248.1 (03/2002) except as noted below, defines
 the protocols used between elements of a physically decomposed
 multimedia gateway.  There are no functional differences from a
 system view between a decomposed gateway, with distributed sub-
 components potentially on more than one physical device, and a
 monolithic gateway such as described in ITU-T Recommendation H.246.
 This document does not define how gateways, multipoint control units
 or interactive voice response units (IVRs) work.  Instead it creates
 a general framework that is suitable for these applications.
 Packet network interfaces may include IP, ATM or possibly others.
 The interfaces will support a variety of Switched Circuit Network
 (SCN) signalling systems, including tone signalling, ISDN, ISUP, QSIG
 and GSM.  National variants of these signalling systems will be
 supported where applicable.

1.1 Changes From RFC 3015

 The differences between this document and RFC 3015 are documented in
 Appendix II.

1.2 Differences From ITU-T Recommendation H.248.1 (03/2002)

 This document differs from the corresponding ITU-T publication in the
 following respects:
  1. Added IETF front matter in place of the corresponding ITU-T

material.

  1. The ITU-T summary is too H.323-specific and has been omitted.

Groves, et al. Standards Track [Page 5] RFC 3525 Gateway Control Protocol June 2003

  1. The IETF conventions have been stated as governing this document.

As discussed in section 5 below, this gives slightly greater

    strength to "should" requirements.
  1. The Scope section (just above) has been edited slightly to suit

its IETF context.

  1. Added normative references to RFCs 2026 and 2119.
  1. Figures 4, 5, and 6 show the centre of the context for greater

clarity. Also added Figure 6a showing an important additional

    example.
  1. Added a paragraph in section 7.1.18 which was approved in the

Implementor's Guide but lost inadvertently in the ITU-T approved

    version.
  1. This document incorporates corrections to the informative examples

in Appendix I which also appear in H.248.1 version 2, but which

    were not picked up in H.248.1 (03/2002).
  1. This document includes a new Appendix II listing all the changes

from RFC 3015.

  1. This document includes an Acknowledgements section listing the

authors of RFC 3015 but also many other people who contributed to

    the development of the Megaco/H.248.x protocol.
  1. Moved the Intellectual Property declaration to its usual place in

an IETF document and added a reference to declarations on the IETF

    web site.

2 References

 The following ITU-T Recommendations and other references contain
 provisions which, through reference in this text, constitute
 provisions of this RFC.  At the time of publication, the editions
 indicated were valid.  All Recommendations and other references are
 subject to revision; all users of this RFC are therefore encouraged
 to investigate the possibility of applying the most recent edition of
 the Recommendations and other references listed below.  A list of the
 currently valid ITU-T Recommendations is regularly published.

2.1 Normative references

  1. ITU-T Recommendation H.225.0 (1999), Call signalling protocols and

media stream packetization for packet-based multimedia

    communication systems.

Groves, et al. Standards Track [Page 6] RFC 3525 Gateway Control Protocol June 2003

  1. ITU-T Recommendation H.235 (1998), Security and encryption for

H-Series (H.323 and other H.245-based) multimedia terminals.

  1. ITU-T Recommendation H.245 (1998), Control protocol for multimedia

communication.

  1. ITU-T Recommendation H.246 (1998), Interworking of H-series

multimedia terminals with H-series multimedia terminals and

    voice/voiceband terminals on GSTN and ISDN.
  1. ITU-T Recommendation H.248.8 (2002), H.248 Error Codes and Service

Change Reasons.

  1. ITU-T Recommendation H.323 (1999), Packet-based multimedia

communication systems.

  1. ITU-T Recommendation I.363.1 (1996), B-ISDN ATM adaptation layer

(AAL) specification: Type 1 AAL.

  1. ITU-T Recommendation I.363.2 (1997), B-ISDN ATM adaptation layer

(AAL) specification: Type 2 AAL.

  1. ITU-T Recommendation I.363.5 (1996), B-ISDN ATM adaptation layer

(AAL) specification: Type 5 AAL.

  1. ITU-T Recommendation I.366.1 (1998), Segmentation and Reassembly

Service Specific Convergence Sublayer for the AAL type 2.

  1. ITU-T Recommendation I.366.2 (1999), AAL type 2 service specific

convergence sublayer for trunking.

  1. ITU-T Recommendation I.371 (2000), Traffic control and congestion

control in B-ISDN.

  1. ITU-T Recommendation Q.763 (1999), Signalling System No. 7 - ISDN

user part formats and codes.

  1. ITU-T Recommendation Q.765.5 (2001), Application transport

mechanism - Bearer independent call control (BICC).

  1. ITU-T Recommendation Q.931 (1998), ISDN user-network interface

layer 3 specification for basic call control.

  1. ITU-T Recommendation Q.2630.1 (1999), AAL type 2 signalling

protocol (Capability Set 1).

Groves, et al. Standards Track [Page 7] RFC 3525 Gateway Control Protocol June 2003

  1. ITU-T Recommendation Q.2931 (1995), Digital Subscriber Signalling

System No. 2 (DSS2) - User-Network Interface (UNI) - Layer 3

    specification for basic call/connection control.
  1. ITU-T Recommendation Q.2941.1 (1997), Digital Subscriber

Signalling System No. 2 - Generic identifier transport.

  1. ITU-T Recommendation Q.2961.1 (1995), Additional signalling

capabilities to support traffic parameters for the tagging option

    and the sustainable call rate parameter set.
  1. ITU-T Recommendation Q.2961.2 (1997), Additional traffic

parameters: Support of ATM transfer capability in the broadband

    bearer capability information element.
  1. ITU-T Recommendation Q.2965.1 (1999), Digital subscriber

signalling system No. 2 - Support of Quality of Service classes.

  1. ITU-T Recommendation Q.2965.2 (1999), Digital subscriber

signalling system No. 2 - Signalling of individual Quality of

    Service parameters.
  1. ITU-T Recommendation V.76 (1996), Generic multiplexer using V.42

LAPM-based procedures.

  1. ITU-T Recommendation X.213 (1995), Information technology - Open

Systems Interconnection - Network service definition plus

    Amendment 1 (1997), Addition of the Internet protocol address
    format identifier.
  1. ITU-T Recommendation X.680 (1997), Information technology -

Abstract Syntax Notation One (ASN.1): Specification of basic

    notation.
  1. ITU-T Recommendation X.690 (1997), Information Technology - ASN.1

Encoding Rules: Specification of Basic Encoding Rules (BER),

    Canonical Encoding Rules (CER) and Distinguished Encoding Rules
    (DER).
  1. ATM Forum (1996), ATM User-Network Interface (UNI) Signalling

Specification - Version 4.0.

 [RFC 1006] Rose, M. and D. Cass, "ISO Transport Service on top of the
            TCP, Version 3", STD 35, RFC 1006, May 1987.
 [RFC 2026] Brander, S., "The Internet Standards Process -- Revision
            3", BCP 9, RFC 2026, October 1996.

Groves, et al. Standards Track [Page 8] RFC 3525 Gateway Control Protocol June 2003

 [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC 2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", RFC 2234, November 1997.
 [RFC 2327] Handley, M. and V. Jacobson, "SDP: Session Description
            Protocol", RFC 2327, April 1998.
 [RFC 2402] Kent, S. and R. Atkinson, "IP Authentication Header", RFC
            2402, November 1998.
 [RFC 2406] Kent, S. and R. Atkinson, "IP Encapsulating Security
            Payload (ESP)", RFC 2406, November 1998.

2.2 Informative references

  1. ITU-T Recommendation E.180/Q.35 (1998), Technical characteristics

of tones for the telephone service.

  1. CCITT Recommendation G.711 (1988), Pulse Code Modulation (PCM) of

voice frequencies.

  1. ITU-T Recommendation H.221 (1999), Frame structure for a 64 to

1920 kbit/s channel in audiovisual teleservices.

  1. ITU T Recommendation H.223 (1996), Multiplexing protocol for low

bit rate multimedia communication.

  1. ITU-T Recommendation H.226 (1998), Channel aggregation protocol

for multilink operation on circuit-switched networks

  1. ITU-T Recommendation Q.724 (1998), Signalling procedures.
  1. ITU-T Recommendation Q.764 (1999), Signalling system No. 7 - ISDN

user part signalling procedures.

  1. ITU-T Recommendation Q.1902.4 (2001), Bearer independent call

control protocol - Basic call procedures.

 [RFC 768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
            August 1980.
 [RFC 791]  Postel, J., "Internet Protocol", STD 5, RFC 791, September
            1981.
 [RFC 793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
            793, September 1981.

Groves, et al. Standards Track [Page 9] RFC 3525 Gateway Control Protocol June 2003

 [RFC 1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD
            51, RFC 1661, July 1994.
 [RFC 1889] Schulzrinne, H., Casner, S., Frederick, R. and V.
            Jacobson, "RTP: A Transport Protocol for Real-Time
            Applications", RFC 1889, January 1996.
 [RFC 1890] Schulzrinne, H. and G. Fokus, "RTP Profile for Audio and
            Video Conferences with Minimal Control",  RFC 1890,
            January 1996.
 [RFC 2401] Kent, S. and R. Atkinson, "Security Architecture for the
            Internet Protocol", RFC 2401, November 1998.
 [RFC 2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", RFC 2460, December 1998.
 [RFC 2543] Handley, M., Schulzrinne, H., Schooler, E. and J.
            Rosenberg, "SIP: Session Initiation Protocol", RFC 2543,
            March 1999.
 [RFC 2805] Greene, N., Ramalho, M. and B. Rosen, "Media Gateway
            Control Protocol Architecture and Requirements", RFC 2805,
            April 2000.

3 Definitions

 This document defines the following terms:
 Access gateway:
 A type of gateway that provides a User-Network Interface (UNI) such
 as ISDN.
 Descriptor:
 A syntactic element of the protocol that groups related properties.
 For instance, the properties of a media flow on the MG can be set by
 the MGC by including the appropriate descriptor in a command.
 Media Gateway (MG):
 The media gateway converts media provided in one type of network to
 the format required in another type of network.  For example, a MG
 could terminate bearer channels from a switched circuit network
 (e.g., DS0s) and media streams from a packet network (e.g., RTP
 streams in an IP network).  This gateway may be capable of processing
 audio, video and T.120 alone or in any combination, and will be
 capable of full duplex media translations.  The MG may also play
 audio/video messages and perform other IVR functions, or may perform
 media conferencing.

Groves, et al. Standards Track [Page 10] RFC 3525 Gateway Control Protocol June 2003

 Media Gateway Controller (MGC):
 Controls the parts of the call state that pertain to connection
 control for media channels in a MG.
 Multipoint Control Unit (MCU):
 An entity that controls the setup and coordination of a multi-user
 conference that typically includes processing of audio, video and
 data.
 Residential gateway:
 A gateway that interworks an analogue line to a packet network.  A
 residential gateway typically contains one or two analogue lines and
 is located at the customer premises.
 SCN FAS signalling gateway:
 This function contains the SCN Signalling Interface that terminates
 SS7, ISDN or other signalling links where the call control channel
 and bearer channels are collocated in the same physical span.
 SCN NFAS signalling gateway:
 This function contains the SCN Signalling Interface that terminates
 SS7 or other signalling links where the call control channels are
 separated from bearer channels.
 Stream:
 Bidirectional media or control flow received/sent by a media gateway
 as part of a call or conference.
 Trunk:
 A communication channel between two switching systems such as a DS0
 on a T1 or E1 line.
 Trunking gateway:
 A gateway between SCN network and packet network that typically
 terminates a large number of digital circuits.

4 Abbreviations

 This RFC document uses the following abbreviations:
 ALF   Application Layer Framing
 ATM   Asynchronous Transfer Mode
 CAS   Channel Associated Signalling
 DTMF  Dual Tone Multi-Frequency

Groves, et al. Standards Track [Page 11] RFC 3525 Gateway Control Protocol June 2003

 FAS   Facility Associated Signalling
 GSM   Global System for Mobile communications
 GW    GateWay
 IANA  Internet Assigned Numbers Authority (superseded by Internet
       Corporation for Assigned Names and Numbers - ICANN)
 IP    Internet Protocol
 ISUP  ISDN User Part
 IVR   Interactive Voice Response
 MG    Media Gateway
 MGC   Media Gateway Controller
 NFAS  Non-Facility Associated Signalling
 PRI   Primary Rate Interface
 PSTN  Public Switched Telephone Network
 QoS   Quality of Service
 RTP   Real-time Transport Protocol
 SCN   Switched Circuit Network
 SG    Signalling Gateway
 SS7   Signalling System No. 7

5 Conventions

 In the H.248.1 Recommendation, "SHALL" refers to a mandatory
 requirement, while "SHOULD" refers to a suggested but optional
 feature or procedure.  The term "MAY" refers to an optional course of
 action without expressing a preference.  Note that these definition
 are overridden in the present document by the RFC 2119 conventions
 stated at the beginning of this document.  RFC 2119 has a more
 precise definition of "should" than is provided by the ITU-T.

Groves, et al. Standards Track [Page 12] RFC 3525 Gateway Control Protocol June 2003

6 Connection model

 The connection model for the protocol describes the logical entities,
 or objects, within the Media Gateway that can be controlled by the
 Media Gateway Controller.  The main abstractions used in the
 connection model are Terminations and Contexts.
 A Termination sources and/or sinks one or more streams.  In a
 multimedia conference, a Termination can be multimedia and sources or
 sinks multiple media streams.  The media stream parameters, as well
 as modem, and bearer parameters are encapsulated within the
 Termination.
 A Context is an association between a collection of Terminations.
 There is a special type of Context, the null Context, which contains
 all Terminations that are not associated to any other Termination.
 For instance, in a decomposed access gateway, all idle lines are
 represented by Terminations in the null Context.
 Following is a graphical depiction of these concepts.  The diagram of
 Figure 1 gives several examples and is not meant to be an
 all-inclusive illustration.  The asterisk box in each of the Contexts
 represents the logical association of Terminations implied by the
 Context.

Groves, et al. Standards Track [Page 13] RFC 3525 Gateway Control Protocol June 2003

       +------------------------------------------------------+
       |Media Gateway                                         |
       | +-------------------------------------------------+  |
       | |Context                          +-------------+ |  |
       | |                                 | Termination | |  |
       | |                                 |-------------| |  |
       | |  +-------------+             +->| SCN Bearer  |<---+->
       | |  | Termination |   +-----+   |  |   Channel   | |  |
       | |  |-------------|   |     |---+  +-------------+ |  |
     <-+--->| RTP Stream  |---|  *  |                      |  |
       | |  |             |   |     |---+  +-------------+ |  |
       | |  +-------------+   +-----+   |  | Termination | |  |
       | |                              |  |-------------| |  |
       | |                              +->| SCN Bearer  |<---+->
       | |                                 |   Channel   | |  |
       | |                                 +-------------+ |  |
       | +-------------------------------------------------+  |
       |                                                      |
       |                                                      |
       |                    +------------------------------+  |
       |   (NULL Context)   |Context                       |  |
       |  +-------------+   |              +-------------+ |  |
       |  | Termination |   | +-----+      | Termination | |  |
       |  |-------------|   | |     |      |-------------| |  |
       |  | SCN Bearer  |   | |  *  |------| SCN Bearer  |<---+->
       |  |   Channel   |   | |     |      |   Channel   | |  |
       |  +-------------+   | +-----+      +-------------+ |  |
       |                    +------------------------------+  |
       |                                                      |
       |                                                      |
       | +-------------------------------------------------+  |
       | |Context                                          |  |
       | |  +-------------+                +-------------+ |  |
       | |  | Termination |   +-----+      | Termination | |  |
       | |  |-------------|   |     |      |-------------| |  |
     <-+--->| SCN Bearer  |---|  *  |------| SCN Bearer  |<---+->
       | |  |   Channel   |   |     |      |   Channel   | |  |
       | |  +-------------+   +-----+      +-------------+ |  |
       | +-------------------------------------------------+  |
       | ___________________________________________________  |
       +------------------------------------------------------+
          Figure 1: Examples of Megaco/H.248 Connection Model

Groves, et al. Standards Track [Page 14] RFC 3525 Gateway Control Protocol June 2003

 The example in Figure 2 shows an example of one way to accomplish a
 call-waiting scenario in a decomposed access gateway, illustrating
 the relocation of a Termination between Contexts.  Terminations T1
 and T2 belong to Context C1 in a two-way audio call.  A second audio
 call is waiting for T1 from Termination T3.  T3 is alone in Context
 C2.  T1 accepts the call from T3, placing T2 on hold.  This action
 results in T1 moving into Context C2, as shown in Figure 3.
       +------------------------------------------------------+
       |Media Gateway                                         |
       | +-------------------------------------------------+  |
       | |Context C1                                       |  |
       | |  +-------------+                +-------------+ |  |
       | |  | Term. T2    |   +-----+      | Term. T1    | |  |
       | |  |-------------|   |     |      |-------------| |  |
     <-+--->| RTP Stream  |---|  *  |------| SCN Bearer  |<---+->
       | |  |             |   |     |      |   Channel   | |  |
       | |  +-------------+   +-----+      +-------------+ |  |
       | +-------------------------------------------------+  |
       |                                                      |
       | +-------------------------------------------------+  |
       | |Context C2                                       |  |
       | |                                 +-------------+ |  |
       | |                    +-----+      | Term. T3    | |  |
       | |                    |     |      |-------------| |  |
       | |                    |  *  |------| SCN Bearer  |<---+->
       | |                    |     |      |   Channel   | |  |
       | |                    +-----+      +-------------+ |  |
       | +-------------------------------------------------+  |
       +------------------------------------------------------+
   Figure 2: Example Call Waiting Scenario / Alerting Applied to T1

Groves, et al. Standards Track [Page 15] RFC 3525 Gateway Control Protocol June 2003

       +------------------------------------------------------+
       |Media Gateway                                         |
       | +-------------------------------------------------+  |
       | |Context C1                                       |  |
       | |  +-------------+                                |  |
       | |  | Term. T2    |   +-----+                      |  |
       | |  |-------------|   |     |                      |  |
     <-+--->| RTP Stream  |---|  *  |                      |  |
       | |  |             |   |     |                      |  |
       | |  +-------------+   +-----+                      |  |
       | +-------------------------------------------------+  |
       |                                                      |
       | +-------------------------------------------------+  |
       | |Context C2                                       |  |
       | |  +-------------+                +-------------+ |  |
       | |  | Term. T1    |   +-----+      | Term. T3    | |  |
       | |  |-------------|   |     |      |-------------| |  |
     <-+--->| SCN Bearer  |---|  *  |------| SCN Bearer  |<---+->
       | |  |   Channel   |   |     |      |   Channel   | |  |
       | |  +-------------+   +-----+      +-------------+ |  |
       | +-------------------------------------------------+  |
       +------------------------------------------------------+
        Figure 3. Example Call Waiting Scenario / Answer by T1

6.1 Contexts

 A Context is an association between a number of Terminations.  The
 Context describes the topology (who hears/sees whom) and the media
 mixing and/or switching parameters if more than two Terminations are
 involved in the association.
 There is a special Context called the null Context.  It contains
 Terminations that are not associated to any other Termination.
 Terminations in the null Context can have their parameters examined
 or modified, and may have events detected on them.
 In general, an Add command is used to add Terminations to Contexts.
 If the MGC does not specify an existing Context to which the
 Termination is to be added, the MG creates a new Context.  A
 Termination may be removed from a Context with a Subtract command,
 and a Termination may be moved from one Context to another with a
 Move command.  A Termination SHALL exist in only one Context at a
 time.

Groves, et al. Standards Track [Page 16] RFC 3525 Gateway Control Protocol June 2003

 The maximum number of Terminations in a Context is a MG property.
 Media gateways that offer only point-to-point connectivity might
 allow at most two Terminations per Context.  Media gateways that
 support multipoint conferences might allow three or more Terminations
 per Context.

6.1.1 Context attributes and descriptors

 The attributes of Contexts are:
  1. ContextID.
  1. The topology (who hears/sees whom).
    The topology of a Context describes the flow of media between the
    Terminations within a Context.  In contrast, the mode of a
    Termination (send/receive/...) describes the flow of the media at
    the ingress/egress of the media gateway.
  1. The priority is used for a Context in order to provide the MG with

information about a certain precedence handling for a Context.

    The MGC can also use the priority to control autonomously the
    traffic precedence in the MG in a smooth way in certain
    situations (e.g., restart), when a lot of Contexts must be handled
    simultaneously.  Priority 0 is the lowest priority and a priority
    of 15 is the highest priority.
  1. An indicator for an emergency call is also provided to allow a

preference handling in the MG.

6.1.2 Creating, deleting and modifying Contexts

 The protocol can be used to (implicitly) create Contexts and modify
 the parameter values of existing Contexts.  The protocol has commands
 to add Terminations to Contexts, subtract them from Contexts, and to
 move Terminations between Contexts.  Contexts are deleted implicitly
 when the last remaining Termination is subtracted or moved out.

6.2 Terminations

 A Termination is a logical entity on a MG that sources and/or sinks
 media and/or control streams.  A Termination is described by a number
 of characterizing Properties, which are grouped in a set of
 Descriptors that are included in commands.  Terminations have unique
 identities (TerminationIDs), assigned by the MG at the time of their
 creation.

Groves, et al. Standards Track [Page 17] RFC 3525 Gateway Control Protocol June 2003

 Terminations representing physical entities have a semi-permanent
 existence.  For example, a Termination representing a TDM channel
 might exist for as long as it is provisioned in the gateway.
 Terminations representing ephemeral information flows, such as RTP
 flows, would usually exist only for the duration of their use.
 Ephemeral Terminations are created by means of an Add command.  They
 are destroyed by means of a Subtract command.  In contrast, when a
 physical Termination is Added to or Subtracted from a Context, it is
 taken from or to the null Context, respectively.
 Terminations may have signals applied to them (see 7.1.11).
 Terminations may be programmed to detect Events, the occurrence of
 which can trigger notification messages to the MGC, or action by the
 MG.  Statistics may be accumulated on a Termination.  Statistics are
 reported to the MGC upon request (by means of the AuditValue command,
 see 7.2.5) and when the Termination is taken out of the call it is
 in.
 Multimedia gateways may process multiplexed media streams.  For
 example, Recommendation H.221 describes a frame structure for
 multiple media streams multiplexed on a number of digital 64 kbit/s
 channels.  Such a case is handled in the connection model in the
 following way.  For every bearer channel that carries part of the
 multiplexed streams, there is a physical or ephemeral "bearer
 Termination".  The bearer Terminations that source/sink the digital
 channels are connected to a separate Termination called the
 "multiplexing Termination".  The multiplexing termination is an
 ephemeral termination representing a frame-oriented session.  The
 MultiplexDescriptor for this Termination describes the multiplex used
 (e.g., H.221 for an H.320 session) and indicates the order in which
 the contained digital channels are assembled into a frame.
 Multiplexing terminations may be cascades (e.g., H.226 multiplex of
 digital channels feeding into a H.223 multiplex supporting an H.324
 session).
 The individual media streams carried in the session are described by
 StreamDescriptors on the multiplexing Termination.  These media
 streams can be associated with streams sourced/sunk by Terminations
 in the Context other than the bearer Terminations supporting the
 multiplexing Termination.  Each bearer Termination supports only a
 single data stream.  These data streams do not appear explicitly as
 streams on the multiplexing Termination and they are hidden from the
 rest of the context.
 Figures 4, 5, 6, and 6a illustrate typical applications of the
 multiplexing termination and Multiplex Descriptor.

Groves, et al. Standards Track [Page 18] RFC 3525 Gateway Control Protocol June 2003

                +-----------------------------------+
                | Context     +-------+             |
               +----+         |       |             |
 Circuit 1 -|--| TC1|---------+ Tmux  |             |
            |  +----+ (Str 1) |       |  Audio    +-----+
            |   |             |       +-----*-----+     |-----
            |  +----+         | H.22x | Stream 1  |     |
 Circuit 2 -|--| TC2|---------+ multi-|           | TR1 |
            |  +----+ (Str 1) | plex  |           |(RTP)|
            |   |             |       |  Video    |     |
            |  +----+         |       +-----*-----+     |-----
 Circuit 3 -|--| TC3|---------+       | Stream 2  |     |
            /  +----+ (Str 1) |       |           +-----+
           /    |             +-------+             |
          /     +-----------------\-----------------+
 Audio, video, and control         \
 signals are carried in frames    Tmux is an ephemeral with two
 spanning the circuits.           explicit Stream Descriptors
                                  and a Multiplex Descriptor.
    Figure 4: Multiplexed Termination Scenario - Circuit to Packet
            (Asterisks * denote the centre of the context)
                  Context
                +--------------------------------------+
                |       +-------+        +-------+     |
               +----+   |       |        |       |   +----+
 Circuit 1 ----| TC1|---+ Tmux1 |  Audio | Tmux2 +---| TC4|---
               +----+   |       +---*----+       |   +----+
                |       |       |  Str 1 |       |     |
               +----+   | H.22x |        | H.22x |   +----+
 Circuit 2 ----| TC2|---+ multi-|        | multi-+---| TC5|---
               +----+   | plex  |        | plex  |   +----+
                |       |       |  Video |       |     |
               +----+   |       +---*----+       |   +----+
 Circuit 3 ----| TC3|---+       |  Str 2 |       +---| TC6|---
               +----+   |       |        |       |   +----+
                |       +-------+        +-------+     |
                +-----------------\-----/--------------+
                                   \   /
           Tmux1 and Tmux2 are ephemerals each with two
          explicit Stream Descriptors and a Multiplex Descriptor.
    Figure 5: Multiplexed Termination Scenario - Circuit to Circuit
            (Asterisks * denote the centre of the context)

Groves, et al. Standards Track [Page 19] RFC 3525 Gateway Control Protocol June 2003

                +-----------------------------------+
                | Context     +-------+             |
               +----+         |       |             |
 Circuit 1 -|--| TC1|---------+ Tmux  |             |
            |  +----+ (Str 1) |       |  Audio    +-----+
            |   |             |       +-----*-----+ TR1 |-----
            |  +----+         | H.22x | Stream 1  |(RTP)|
 Circuit 2 -|--| TC2|---------+ multi-|           +-----+
            |  +----+ (Str 1) | plex  |             |
            |   |             |       |  Video    +-----+
            |  +----+         |       +-----*-----+ TR2 |-----
 Circuit 3 -|--| TC3|---------+       | Stream 2  |(RTP)|
            /  +----+ (Str 1) |       |           +-----+
           /    |             +-------+             |
          /     +-----------------\-----------------+
 Audio, video, and control         \ Tmux is an ephemeral with two
 signals are carried in frames    explicit Stream Descriptors and
 spanning the circuits.           and a Multiplex Descriptor.
    Figure 6: Multiplexed Termination Scenario - Single to Multiple
                             Terminations
            (Asterisks * denote the centre of the context)
          Context
        +---------------------------------------------+
        |       +-------+       +-------+             |
 Cct 1 +----+   |       |       |       | Audio     +-----+
   ----| TC1|---+ Tmux1 |       | Tmux2 +-----*-----| TR1 |-----
       +----+   |       |       |       | Stream 1  |(RTP)|
        |       |       | Data  |       |           +-----+
 Cct 2 +----+   | H.226 +-------+ H.223 |             |
   ----| TC2|---+ multi-|(Str 1)| multi-| Control   +-----+
       +----+   | plex  |       | plex  +-----*-----+ Tctl|-----
        |       |       |       |       | Stream 3  +-----+
 Cct 3 +----+   |       |       |       |             |
   ----| TC3|---+       |       |       |           +-----+
       +----+   |       |       |       +-----*-----+ TR2 |-----
        |       +-------+       |       |  Video    |(RTP)|
        |                       +-------+ Stream 2  +-----+
        |                                             |
        +---------------------------------------------+
      Tmux1 has a Multiplex Descriptor and a single data stream.
      Tmux2 has a Multiplex Descriptor with a single bearer and
      three explicit Stream Descriptors.
  Figure 6a: Multiplexed Termination Scenario - Cascaded Multiplexes
            (Asterisks * denote the centre of the context)
   Note: this figure does not appear in Rec.  H.248.1

Groves, et al. Standards Track [Page 20] RFC 3525 Gateway Control Protocol June 2003

 Terminations may be created which represent multiplexed bearers, such
 as an ATM AAL Type 2 bearer.  When a new multiplexed bearer is to be
 created, an ephemeral Termination is created in a Context established
 for this purpose.  When the Termination is subtracted, the
 multiplexed bearer is destroyed.

6.2.1 Termination dynamics

 The protocol can be used to create new Terminations and to modify
 property values of existing Terminations.  These modifications
 include the possibility of adding or removing events and/or signals.
 The Termination properties, and events and signals are described in
 the ensuing subclauses.  An MGC can only release/modify Terminations
 and the resources that the Termination represents which it has
 previously seized via, e.g., the Add command.

6.2.2 TerminationIDs

 Terminations are referenced by a TerminationID, which is an arbitrary
 schema chosen by the MG.
 TerminationIDs of physical Terminations are provisioned in the Media
 Gateway.  The TerminationIDs may be chosen to have structure.  For
 instance, a TerminationID may consist of trunk group and a trunk
 within the group.
 A wildcarding mechanism using two types of wildcards can be used with
 TerminationIDs.  The two wildcards are ALL and CHOOSE.  The former is
 used to address multiple Terminations at once, while the latter is
 used to indicate to a media gateway that it must select a Termination
 satisfying the partially specified TerminationID.  This allows, for
 instance, that a MGC instructs a MG to choose a circuit within a
 trunk group.
 When ALL is used in the TerminationID of a command, the effect is
 identical to repeating the command with each of the matching
 TerminationIDs.  The use of ALL does not address the ROOT
 termination.  Since each of these commands may generate a response,
 the size of the entire response may be large.  If individual
 responses are not required, a wildcard response may be requested.  In
 such a case, a single response is generated, which contains the UNION
 of all of the individual responses which otherwise would have been
 generated, with duplicate values suppressed.  For instance, given a
 Termination Ta with properties p1=a, p2=b and Termination Tb with

Groves, et al. Standards Track [Page 21] RFC 3525 Gateway Control Protocol June 2003

 properties p2=c, p3=d, a UNION response would consist of a wildcarded
 TerminationId and the sequence of properties p1=a, p2=b,c and p3=d.
 Wildcard response may be particularly useful in the Audit commands.
 The encoding of the wildcarding mechanism is detailed in Annexes A
 and B.

6.2.3 Packages

 Different types of gateways may implement Terminations that have
 widely differing characteristics.  Variations in Terminations are
 accommodated in the protocol by allowing Terminations to have
 optional Properties, Events, Signals and Statistics implemented by
 MGs.
 In order to achieve MG/MGC interoperability, such options are grouped
 into Packages, and typically a Termination realizes a set of such
 Packages.  More information on definition of packages can be found in
 clause 12.  An MGC can audit a Termination to determine which
 Packages it realizes.
 Properties, Events, Signals and Statistics defined in Packages, as
 well as parameters to them, are referenced by identifiers (Ids).
 Identifiers are scoped.  For each package, PropertyIds, EventIds,
 SignalIds, StatisticsIds and ParameterIds have unique name spaces and
 the same identifier may be used in each of them.  Two PropertyIds in
 different packages may also have the same identifier, etc.
 To support a particular package the MG must support all properties,
 signals, events and statistics defined in a package.  It must also
 support all Signal and Event parameters.  The MG may support a subset
 of the values listed in a package for a particular Property or
 Parameter.
 When packages are extended, the properties, events, signals and
 statistics defined in the base package can be referred to using
 either the extended package name or the base package name.  For
 example, if Package A defines event e1, and Package B extends Package
 A, then B/e1 is an event for a termination implementing Package B. By
 definition, the MG MUST also implement the base Package, but it is
 optional to publish the base package as an allowed interface.  If it
 does publish  A, then A would be reported on the Package Descriptor
 in AuditValue as well as B, and event A/e1 would be available on a
 termination.  If the MG does not publish A, then only B/e1 would be
 available.  If published through AuditValue, A/e1 and B/e1 are the
 same event.

Groves, et al. Standards Track [Page 22] RFC 3525 Gateway Control Protocol June 2003

 For improved interoperability and backward compatibility, an MG MAY
 publish all Packages supported by its Terminations, including base
 Packages from which extended Packages are derived.  An exception to
 this is in cases where the base packages are expressly "Designed to
 be extended only".

6.2.4 Termination properties and descriptors

 Terminations have properties.  The properties have unique
 PropertyIDs. Most properties have default values, which are
 explicitly defined in this protocol specification or in a package
 (see clause 12) or set by provisioning.  If not provisioned
 otherwise, the properties in all descriptors except TerminationState
 and LocalControl default to empty/"no value" when a Termination is
 first created or returned to the null Context.  The default contents
 of the two exceptions are described in 7.1.5 and 7.1.7.
 The provisioning of a property value in the MG will override any
 default value, be it supplied in this protocol specification or in a
 package.  Therefore if it is essential for the MGC to have full
 control over the property values of a Termination, it should supply
 explicit values when ADDing the Termination to a Context.
 Alternatively, for a physical Termination the MGC can determine any
 provisioned property values by auditing the Termination while it is
 in the NULL Context.
 There are a number of common properties for Terminations and
 properties specific to media streams.  The common properties are also
 called the Termination state properties.  For each media stream,
 there are local properties and properties of the received and
 transmitted flows.
 Properties not included in the base protocol are defined in Packages.
 These properties are referred to by a name consisting of the
 PackageName and a PropertyId.  Most properties have default values
 described in the Package description.  Properties may be read-only or
 read/write.  The possible values of a property may be audited, as can
 their current values.  For properties that are read/write, the MGC
 can set their values.  A property may be declared as "Global" which
 has a single value shared by all Terminations realizing the package.
 Related properties are grouped into descriptors for convenience.
 When a Termination is added to a Context, the value of its read/write
 properties can be set by including the appropriate descriptors as
 parameters to the Add command.  Similarly, a property of a
 Termination in a Context may have its value changed by the Modify
 command.

Groves, et al. Standards Track [Page 23] RFC 3525 Gateway Control Protocol June 2003

 Properties may also have their values changed when a Termination is
 moved from one Context to another as a result of a Move command.  In
 some cases, descriptors are returned as output from a command.
 In general, if a Descriptor is completely omitted from one of the
 aforementioned Commands, the properties in that Descriptor retain
 their prior values for the Termination(s) upon which the Command
 acts.  On the other hand, if some read/write properties are omitted
 from a Descriptor in a Command (i.e., the Descriptor is only
 partially specified), those properties will be reset to their default
 values for the Termination(s) upon which the Command acts, unless the
 package specifies other behavior.  For more details, see clause 7.1
 dealing with the individual Descriptors.
 The following table lists all of the possible descriptors and their
 use.  Not all descriptors are legal as input or output parameters to
 every command.
 Descriptor name  Description
 Modem            Identifies modem type and properties when
                  applicable
 Mux              Describes multiplex type for multimedia
                  Terminations (e.g., H.221, H.223, H.225.0) and
                  Terminations forming the input mux
 Media            A list of media stream specifications (see 7.1.4)
 TerminationState Properties of a Termination (which can be defined
                  in Packages) that are not stream specific
 Stream           A list of remote/local/localControl descriptors for
                  a single stream
 Local            Contains properties that specify the media flows
                  that the MG receives from the remote entity.
 Remote           Contains properties that specify the media flows
                  that the MG sends to the remote entity.
 LocalControl     Contains properties (which can be defined in
                  packages) that are of interest between the MG and
                  the MGC.
 Events           Describes events to be detected by the MG and what
                  to do when an event is detected.

Groves, et al. Standards Track [Page 24] RFC 3525 Gateway Control Protocol June 2003

 EventBuffer      Describes events to be detected by the MG when
                  Event Buffering is active.
 Signals          Describes signals (see 7.1.11) applied  to
                  Terminations.
 Audit            In Audit commands, identifies which information is
                  desired.
 Packages         In AuditValue, returns a list of Packages realized
                  by Termination.
 DigitMap         Defines patterns against which sequences of a
                  specified set of events are to be matched so they
                  can be reported as a group rather than singly.
 ServiceChange    In ServiceChange, what, why service change
                  occurred, etc.
 ObservedEvents   In Notify or AuditValue, report of events observed.
 Statistics       In Subtract and Audit, report of Statistics kept on
                  a Termination.
 Topology         Specifies flow directions between Terminations in a
                  Context.
 Error            Contains an error code and optionally error text;
                  it may occur in command replies and in Notify
                  requests.

6.2.5 Root Termination

 Occasionally, a command must refer to the entire gateway, rather than
 a Termination within it.  A special TerminationID, "Root" is reserved
 for this purpose.  Packages may be defined on Root.  Root thus may
 have properties, events and statistics (signals are not appropriate
 for root).  Accordingly, the root TerminationID may appear in:
  1. a Modify command - to change a property or set an event
  1. a Notify command - to report an event
  1. an AuditValue return - to examine the values of properties and

statistics implemented on root

  1. an AuditCapability - to determine what properties of root are

implemented

Groves, et al. Standards Track [Page 25] RFC 3525 Gateway Control Protocol June 2003

  1. a ServiceChange - to declare the gateway in or out of service.
 Any other use of the root TerminationID is an error.  Error code
 410 - Incorrect identifier shall be returned in these cases.

7 Commands

 The protocol provides commands for manipulating the logical entities
 of the protocol connection model, Contexts and Terminations.
 Commands provide control at the finest level of granularity supported
 by the protocol.  For example, Commands exist to add Terminations to
 a Context, modify Terminations, subtract Terminations from a Context,
 and audit properties of Contexts or Terminations.  Commands provide
 for complete control of the properties of Contexts and Terminations.
 This includes specifying which events a Termination is to report,
 which signals/actions are to be applied to a Termination and
 specifying the topology of a Context (who hears/sees whom).
 Most commands are for the specific use of the Media Gateway
 Controller as command initiator in controlling Media Gateways as
 command responders.  The exceptions are the Notify and ServiceChange
 commands: Notify is sent from Media Gateway to Media Gateway
 Controller, and ServiceChange may be sent by either entity.  Below is
 an overview of the commands; they are explained in more detail in
 7.2.
 1) Add - The Add command adds a Termination to a Context.  The Add
    command on the first Termination in a Context is used to create a
    Context.
 2) Modify - The Modify command modifies the properties, events and
    signals of a Termination.
 3) Subtract - The Subtract command disconnects a Termination from its
    Context and returns statistics on the Termination's participation
    in the Context.  The Subtract command on the last Termination in a
    Context deletes the Context.
 4) Move - The Move command atomically moves a Termination to another
    Context.
 5) AuditValue - The AuditValue command returns the current state of
    properties, events, signals and statistics of Terminations.
 6) AuditCapabilities - The AuditCapabilities command returns all the
    possible values for Termination properties, events and signals
    allowed by the Media Gateway.

Groves, et al. Standards Track [Page 26] RFC 3525 Gateway Control Protocol June 2003

 7) Notify - The Notify command allows the Media Gateway to inform the
    Media Gateway Controller of the occurrence of events in the Media
    Gateway.
 8) ServiceChange - The ServiceChange command allows the Media Gateway
    to notify the Media Gateway Controller that a Termination or group
    of Terminations is about to be taken out of service or has just
    been returned to service.  ServiceChange is also used by the MG to
    announce its availability to a MGC (registration), and to notify
    the MGC of impending or completed restart of the MG.  The MGC may
    announce a handover to the MG by sending it a ServiceChange
    command.  The MGC may also use ServiceChange to instruct the MG to
    take a Termination or group of Terminations in or out of service.
 These commands are detailed in 7.2.1 through 7.2.8.

7.1 Descriptors

 The parameters to a command are termed Descriptors.  A descriptor
 consists of a name and a list of items.  Some items may have values.
 Many Commands share common descriptors.  This subclause enumerates
 these descriptors.  Descriptors may be returned as output from a
 command.  In any such return of descriptor contents, an empty
 descriptor is represented by its name unaccompanied by any list.
 Parameters and parameter usage specific to a given Command type are
 described in the subclause that describes the Command.

7.1.1 Specifying parameters

 Command parameters are structured into a number of descriptors.  In
 general, the text format of descriptors is
 DescriptorName=<someID>{parm=value, parm=value, ...}.
 Parameters may be fully specified, overspecified or underspecified:
 1) Fully specified parameters have a single, unambiguous value that
    the command initiator is instructing the command responder to use
    for the specified parameter.
 2) Underspecified parameters, using the CHOOSE value, allow the
    command responder to choose any value it can support.
 3) Overspecified parameters have a list of potential values.  The
    list order specifies the command initiator's order of preference
    of selection.  The command responder chooses one value from
    the offered list and returns that value to the command initiator.

Groves, et al. Standards Track [Page 27] RFC 3525 Gateway Control Protocol June 2003

 If a required descriptor other than the Audit descriptor is
 unspecified (i.e., entirely absent) from a command, the previous
 values set in that descriptor for that Termination, if any, are
 retained.  In commands other than Subtract, a missing Audit
 descriptor is equivalent to an empty Audit descriptor.  The Behaviour
 of the MG with respect to unspecified parameters within a descriptor
 varies with the descriptor concerned, as indicated in succeeding
 subclauses.  Whenever a parameter is underspecified or overspecified,
 the descriptor containing the value chosen by the responder is
 included as output from the command.
 Each command specifies the TerminationId the command operates on.
 This TerminationId may be "wildcarded".  When the TerminationId of a
 command is wildcarded, the effect shall be as if the command was
 repeated with each of the TerminationIds matched.

7.1.2 Modem descriptor

 The Modem descriptor specifies the modem type and parameters, if any,
 required for use in e.g., H.324 and text conversation.  The
 descriptor includes the following modem types: V.18, V.22, V.22 bis,
 V.32, V.32 bis, V.34, V.90, V.91, Synchronous ISDN, and allows for
 extensions.  By default, no Modem descriptor is present in a
 Termination.

7.1.3 Multiplex descriptor

 In multimedia calls, a number of media streams are carried on a
 (possibly different) number of bearers.  The multiplex descriptor
 associates the media and the bearers.  The descriptor includes the
 multiplex type:
  1. H.221;
  1. H.223;
  1. H.226;
  1. V.76;
  1. possible extensions,
 and a set of TerminationIDs representing the multiplexed bearers, in
 order.  For example:
    Mux = H.221{ MyT3/1/2, MyT3/2/13, MyT3/3/6, MyT3/21/22}

Groves, et al. Standards Track [Page 28] RFC 3525 Gateway Control Protocol June 2003

7.1.4 Media descriptor

 The Media descriptor specifies the parameters for all the media
 streams.  These parameters are structured into two descriptors: a
 TerminationState descriptor, which specifies the properties of a
 Termination that are not stream dependent, and one or more Stream
 descriptors each of which describes a single media stream.
 A stream is identified by a StreamID.  The StreamID is used to link
 the streams in a Context that belong together.  Multiple streams
 exiting a Termination shall be synchronized with each other.  Within
 the Stream descriptor, there are up to three subsidiary descriptors:
 LocalControl, Local, and Remote.  The relationship between these
 descriptors is thus:
 Media descriptor
    TerminationState Descriptor
    Stream descriptor
       LocalControl descriptor
       Local descriptor
       Remote descriptor
 As a convenience, LocalControl, Local, or Remote descriptors may be
 included in the Media descriptor without an enclosing Stream
 descriptor.  In this case, the StreamID is assumed to be 1.

7.1.5 TerminationState descriptor

 The TerminationState descriptor contains the ServiceStates property,
 the EventBufferControl property and properties of a Termination
 (defined in Packages) that are not stream specific.
 The ServiceStates property describes the overall state of the
 Termination (not stream specific).  A Termination can be in one of
 the following states: "test", "out of service", or "in service".  The
 "test" state indicates that the Termination is being tested.  The
 state "out of service" indicates that the Termination cannot be used
 for traffic.  The state "in service" indicates that a Termination can
 be used or is being used for normal traffic.  "in service" is the
 default state.

Groves, et al. Standards Track [Page 29] RFC 3525 Gateway Control Protocol June 2003

 Values assigned to Properties may be simple values
 (integer/string/enumeration) or may be underspecified, where more
 than one value is supplied and the MG may make a choice:
  1. Alternative Values - multiple values in a list, one of which must

be selected

  1. Ranges - minimum and maximum values, any value between min and max

must be selected, boundary values included

  1. Greater Than/Less Than - value must be greater/less than specified

value

  1. CHOOSE Wildcard - the MG chooses from the allowed values for the

property

 The EventBufferControl property specifies whether events are buffered
 following detection of an event in the Events descriptor, or
 processed immediately.  See 7.1.9 for details.

7.1.6 Stream descriptor

 A Stream descriptor specifies the parameters of a single
 bidirectional stream.  These parameters are structured into three
 descriptors: one that contains Termination properties specific to a
 stream and one each for local and remote flows.  The Stream
 Descriptor includes a StreamID which identifies the stream.  Streams
 are created by specifying a new StreamID on one of the Terminations
 in a Context.  A stream is deleted by setting empty Local and Remote
 descriptors for the stream with ReserveGroup and ReserveValue in
 LocalControl set to "false" on all Terminations in the Context that
 previously supported that stream.
 StreamIDs are of local significance between MGC and MG and they are
 assigned by the MGC.  Within a Context, StreamID is a means by which
 to indicate which media flows are interconnected: streams with the
 same StreamID are connected.
 If a Termination is moved from one Context to another, the effect on
 the Context to which the Termination is moved is the same as in the
 case that a new Termination were added with the same StreamIDs as the
 moved Termination.

Groves, et al. Standards Track [Page 30] RFC 3525 Gateway Control Protocol June 2003

7.1.7 LocalControl descriptor

 The LocalControl descriptor contains the Mode property, the
 ReserveGroup and ReserveValue properties and properties of a
 Termination (defined in Packages) that are stream specific, and are
 of interest between the MG and the MGC.  Values of properties may be
 underspecified as in 7.1.1.
 The allowed values for the mode property are send-only, receive-only,
 send/receive, inactive and loop-back. "Send" and "receive" are with
 respect to the exterior of the Context, so that, for example, a
 stream set to mode=sendOnly does not pass received media into the
 Context.  The default value for the mode property is "Inactive".
 Signals and Events are not affected by mode.
 The boolean-valued Reserve properties, ReserveValue and ReserveGroup,
 of a Termination indicate what the MG is expected to do when it
 receives a Local and/or Remote descriptor.
 If the value of a Reserve property is True, the MG SHALL reserve
 resources for all alternatives specified in the Local and/or Remote
 descriptors for which it currently has resources available.  It SHALL
 respond with the alternatives for which it reserves resources.  If it
 cannot not support any of the alternatives, it SHALL respond with a
 reply to the MGC that contains empty Local and/or Remote descriptors.
 If media begins to flow while more than a single alternative is
 reserved, media packets may be sent/received on any of the
 alternatives and must be processed, although only a single
 alternative may be active at any given time.
 If the value of a Reserve property is False, the MG SHALL choose one
 of the alternatives specified in the Local descriptor (if present)
 and one of the alternatives specified in the Remote descriptor (if
 present).  If the MG has not yet reserved resources to support the
 selected alternative, it SHALL reserve the resources.  If, on the
 other hand, it already reserved resources for the Termination
 addressed (because of a prior exchange with ReserveValue and/or
 ReserveGroup equal to True), it SHALL release any excess resources it
 reserved previously.  Finally, the MG shall send a reply to the MGC
 containing the alternatives for the Local and/or Remote descriptor
 that it selected.  If the MG does not have sufficient resources to
 support any of the alternatives specified, it SHALL respond with
 error 510 (insufficient resources).
 The default value of ReserveValue and ReserveGroup is False.  More
 information on the use of the two Reserve properties is provided in
 7.1.8.

Groves, et al. Standards Track [Page 31] RFC 3525 Gateway Control Protocol June 2003

 A new setting of the LocalControl Descriptor completely replaces the
 previous setting of that descriptor in the MG.  Thus, to retain
 information from the previous setting, the MGC must include that
 information in the new setting.  If the MGC wishes to delete some
 information from the existing descriptor, it merely resends the
 descriptor (in a Modify command) with the unwanted information
 stripped out.

7.1.8 Local and Remote descriptors

 The MGC uses Local and Remote descriptors to reserve and commit MG
 resources for media decoding and encoding for the given Stream(s) and
 Termination to which they apply.  The MG includes these descriptors
 in its response to indicate what it is actually prepared to support.
 The MG SHALL include additional properties and their values in its
 response if these properties are mandatory yet not present in the
 requests made by the MGC (e.g., by specifying detailed video encoding
 parameters where the MGC only specified the payload type).
 Local refers to the media received by the MG and Remote refers to the
 media sent by the MG.
 When text encoding the protocol, the descriptors consist of session
 descriptions as defined in SDP (RFC 2327).  In session descriptions
 sent from the MGC to the MG, the following exceptions to the syntax
 of RFC 2327 are allowed:
  1. the "s=", "t=" and "o=" lines are optional;
  1. the use of CHOOSE is allowed in place of a single parameter value;

and

  1. the use of alternatives is allowed in place of a single parameter

value.

 A Stream Descriptor specifies a single bi-directional media stream
 and so a single session description MUST NOT include more than one
 media description ("m=" line).  A Stream Descriptor may contain
 additional session descriptions as alternatives.  Each media stream
 for a termination must appear in distinct Stream Descriptors.  When
 multiple session descriptions are provided in one descriptor, the
 "v=" lines are required as delimiters; otherwise they are optional in
 session descriptions sent to the MG.  Implementations shall accept
 session descriptions that are fully conformant to RFC 2327.  When
 binary encoding the protocol the descriptor consists of groups of
 properties (tag-value pairs) as specified in Annex C.  Each such
 group may contain the parameters of a session description.

Groves, et al. Standards Track [Page 32] RFC 3525 Gateway Control Protocol June 2003

 Below, the semantics of the Local and Remote descriptors are
 specified in detail.  The specification consists of two parts.  The
 first part specifies the interpretation of the contents of the
 descriptor.  The second part specifies the actions the MG must take
 upon receiving the Local and Remote descriptors.  The actions to be
 taken by the MG depend on the values of the ReserveValue and
 ReserveGroup properties of the LocalControl descriptor.
 Either the Local or the Remote descriptor or both may be:
 1) unspecified (i.e., absent);
 2) empty;
 3) underspecified through use of CHOOSE in a property value;
 4) fully specified; or
 5) overspecified through presentation of multiple groups of
    properties and possibly multiple property values in one or more of
    these groups.
 Where the descriptors have been passed from the MGC to the MG, they
 are interpreted according to the rules given in 7.1.1, with the
 following additional comments for clarification:
 a) An unspecified Local or Remote descriptor is considered to be a
    missing mandatory parameter.  It requires the MG to use whatever
    was last specified for that descriptor.  It is possible that there
    was no previously specified value, in which case the descriptor
    concerned is ignored in further processing of the command.
 b) An empty Local (Remote) descriptor in a message from the MGC
    signifies a request to release any resources reserved for the
    media flow received (sent).
 c) If multiple groups of properties are present in a Local or Remote
    descriptor or multiple values within a group, the order of
    preference is descending.
 d) Underspecified or overspecified properties within a group of
    properties sent by the MGC are requests for the MG to choose one
    or more values which it can support for each of those properties.
    In case of an overspecified property, the list of values is in
    descending order of preference.
 Subject to the above rules, subsequent action depends on the values
 of the ReserveValue and ReserveGroup properties in LocalControl.

Groves, et al. Standards Track [Page 33] RFC 3525 Gateway Control Protocol June 2003

 If ReserveGroup is True, the MG reserves the resources required to
 support any of the requested property group alternatives that it can
 currently support.  If ReserveValue is True, the MG reserves the
 resources required to support any of the requested property value
 alternatives that it can currently support.
 NOTE - If a Local or Remote descriptor contains multiple groups of
 properties, and ReserveGroup is True, then the MG is requested to
 reserve resources so that it can decode or encode the media stream
 according to any of the alternatives.  For instance, if the Local
 descriptor contains two groups of properties, one specifying
 packetized G.711 A-law audio and the other G.723.1 audio, the MG
 reserves resources so that it can decode one audio stream encoded in
 either G.711 A-law format or G.723.1 format.  The MG does not have to
 reserve resources to decode two audio streams simultaneously, one
 encoded in G.711 A-law and one in G.723.1.  The intention for the use
 of ReserveValue is analogous.
 If ReserveGroup is true or ReserveValue is True, then the following
 rules apply:
  1. If the MG has insufficient resources to support all alternatives

requested by the MGC and the MGC requested resources in both Local

    and Remote, the MG should reserve resources to support at least
    one alternative each within Local and Remote.
  1. If the MG has insufficient resources to support at least one

alternative within a Local (Remote) descriptor received from the

    MGC, it shall return an empty Local (Remote) in response.
  1. In its response to the MGC, when the MGC included Local and Remote

descriptors, the MG SHALL include Local and Remote descriptors for

    all groups of properties and property values it reserved resources
    for.  If the MG is incapable of supporting at least one of the
    alternatives within the Local (Remote) descriptor received from
    the MGC, it SHALL return an empty Local (Remote) descriptor.
  1. If the Mode property of the LocalControl descriptor is RecvOnly,

SendRecv, or LoopBack, the MG must be prepared to receive media

    encoded according to any of the alternatives included in its
    response to the MGC.
 If ReserveGroup is False and ReserveValue is False, then the MG
 SHOULD apply the following rules to resolve Local and Remote to a
 single alternative each:
  1. The MG chooses the first alternative in Local for which it is able

to support at least one alternative in Remote.

Groves, et al. Standards Track [Page 34] RFC 3525 Gateway Control Protocol June 2003

  1. If the MG is unable to support at least one Local and one Remote

alternative, it returns Error 510 (Insufficient Resources).

  1. The MG returns its selected alternative in each of Local and

Remote.

 A new setting of a Local or Remote descriptor completely replaces the
 previous setting of that descriptor in the MG.  Thus, to retain
 information from the previous setting, the MGC must include that
 information in the new setting.  If the MGC wishes to delete some
 information from the existing descriptor, it merely resends the
 descriptor (in a Modify command) with the unwanted information
 stripped out.

7.1.9 Events descriptor

 The EventsDescriptor parameter contains a RequestIdentifier and a
 list of events that the Media Gateway is requested to detect and
 report.  The RequestIdentifier is used to correlate the request with
 the notifications that it may trigger.  Requested events include, for
 example, fax tones, continuity test results, and on-hook and off-hook
 transitions.  The RequestIdentifier is omitted if the
 EventsDescriptor is empty (i.e., no events are specified).
 Each event in the descriptor contains the Event name, an optional
 streamID, an optional KeepActive flag, and optional parameters.  The
 Event name consists of a Package Name (where the event is defined)
 and an EventID.  The ALL wildcard may be used for the EventID,
 indicating that all events from the specified package have to be
 detected.  The default streamID is 0, indicating that the event to be
 detected is not related to a particular media stream.  Events can
 have parameters.  This allows a single event description to have some
 variation in meaning without creating large numbers of individual
 events.  Further event parameters are defined in the package.
 If a digit map completion event is present or implied in the
 EventsDescriptor, the EventDM parameter is used to carry either the
 name or the value of the associated digit map.  See 7.1.14 for
 further details.
 When an event is processed against the contents of an active Events
 Descriptor and found to be present in that descriptor ("recognized"),
 the default action of the MG is to send a Notify command to the MGC.
 Notification may be deferred if the event is absorbed into the
 current dial string of an active digit map (see 7.1.14).  Any other
 action is for further study.  Moreover, event recognition may cause
 currently active signals to stop, or may cause the current Events
 and/or Signals descriptor to be replaced, as described at the end of

Groves, et al. Standards Track [Page 35] RFC 3525 Gateway Control Protocol June 2003

 this subclause.  Unless the Events Descriptor is replaced by another
 Events Descriptor, it remains active after an event has been
 recognized.
 If the value of the EventBufferControl property equals LockStep,
 following detection of such an event, normal handling of events is
 suspended.  Any event which is subsequently detected and occurs in
 the EventBuffer descriptor is added to the end of the EventBuffer (a
 FIFO queue), along with the time that it was detected.  The MG SHALL
 wait for a new EventsDescriptor to be loaded.  A new EventsDescriptor
 can be loaded either as the result of receiving a command with a new
 EventsDescriptor, or by activating an embedded EventsDescriptor.
 If EventBufferControl equals Off, the MG continues processing based
 on the active EventsDescriptor.
 In the case of an embedded EventsDescriptor being activated, the MG
 continues event processing based on the newly activated
 EventsDescriptor.
   NOTE 1 - For purposes of EventBuffer handling, activation of an
   embedded EventsDescriptor is equivalent to receipt of a new
   EventsDescriptor.
 When the MG receives a command with a new EventsDescriptor, one or
 more events may have been buffered in the EventBuffer in the MG.  The
 value of EventBufferControl then determines how the MG treats such
 buffered events.
 Case 1
 If EventBufferControl equals LockStep and the MG receives a new
 EventsDescriptor, it will check the FIFO EventBuffer and take the
 following actions:
 1) If the EventBuffer is empty, the MG waits for detection of events
    based on the new EventsDescriptor.
 2) If the EventBuffer is non-empty, the MG processes the FIFO queue
    starting with the first event:
    a) If the event in the queue is in the events listed in the new
       EventsDescriptor, the MG acts on the event and removes the
       event from the EventBuffer.  The time stamp of the Notify shall
       be the time the event was actually detected.  The MG then waits
       for a new EventsDescriptor.  While waiting for a new
       EventsDescriptor, any events detected that appear in the

Groves, et al. Standards Track [Page 36] RFC 3525 Gateway Control Protocol June 2003

       EventsBufferDescriptor will be placed in the EventBuffer.  When
       a new EventsDescriptor is received, the event processing will
       repeat from step 1.
    b) If the event is not in the new EventsDescriptor, the MG SHALL
       discard the event and repeat from step 1.
 Case 2
 If EventBufferControl equals Off and the MG receives a new
 EventsDescriptor, it processes new events with the new
 EventsDescriptor.
 If the MG receives a command instructing it to set the value of
 EventBufferControl to Off, all events in the EventBuffer SHALL be
 discarded.
 The MG may report several events in a single Transaction as long as
 this does not unnecessarily delay the reporting of individual events.
 For procedures regarding transmitting the Notify command, refer to
 the appropriate annex or Recommendation of the H.248 sub-series for
 specific transport considerations.
 The default value of EventBufferControl is Off.
   NOTE 2 - Since the EventBufferControl property is in the
   TerminationStateDescriptor, the MG might receive a command that
   changes the EventBufferControl property and does not include an
   EventsDescriptor.
 Normally, recognition of an event shall cause any active signals to
 stop.  When KeepActive is specified in the event, the MG shall not
 interrupt any signals active on the Termination on which the event is
 detected.
 An event can include an Embedded Signals descriptor and/or an
 Embedded Events descriptor which, if present, replaces the current
 Signals/Events descriptor when the event is recognized.  It is
 possible, for example, to specify that the dial-tone Signal be
 generated when an off-hook Event is recognized, or that the dial-tone
 Signal be stopped when a digit is recognized.  A media gateway
 controller shall not send EventsDescriptors with an event both marked
 KeepActive and containing an embedded SignalsDescriptor.

Groves, et al. Standards Track [Page 37] RFC 3525 Gateway Control Protocol June 2003

 Only one level of embedding is permitted.  An embedded
 EventsDescriptor SHALL NOT contain another embedded EventsDescriptor;
 an embedded EventsDescriptor MAY contain an embedded
 SignalsDescriptor.
 An EventsDescriptor received by a media gateway replaces any previous
 Events descriptor.  Event notification in process shall complete, and
 events detected after the command containing the new EventsDescriptor
 executes, shall be processed according to the new EventsDescriptor.
 An empty Events Descriptor disables all event recognition and
 reporting.  An empty EventBuffer Descriptor clears the EventBuffer
 and disables all event accumulation in LockStep mode: the only events
 reported will be those occurring while an Events Descriptor is
 active.  If an empty Events Descriptor is activated while the
 Termination is operating in LockStep mode, the events buffer is
 immediately cleared.

7.1.10 EventBuffer descriptor

 The EventBuffer descriptor contains a list of events, with their
 parameters if any, that the MG is requested to detect and buffer when
 EventBufferControl equals LockStep (see 7.1.9).

7.1.11 Signals descriptor

 Signals are MG generated media such as tones and announcements as
 well as bearer-related signals such as hookswitch.  More complex
 signals may include a sequence of such simple signals interspersed
 with and conditioned upon the receipt and analysis of media or
 bearer-related signals.  Examples include echoing of received data as
 in Continuity Test package.  Signals may also request preparation of
 media content for future signals.
 A SignalsDescriptor is a parameter that contains the set of signals
 that the Media Gateway is asked to apply to a Termination.  A
 SignalsDescriptor contains a number of signals and/or sequential
 signal lists.  A SignalsDescriptor may contain zero signals and
 sequential signal lists.  Support of sequential signal lists is
 optional.
 Signals are defined in packages.  Signals shall be named with a
 Package name (in which the signal is defined) and a SignalID.  No
 wildcard shall be used in the SignalID.  Signals that occur in a
 SignalsDescriptor have an optional StreamID parameter (default is 0,
 to indicate that the signal is not related to a particular media
 stream), an optional signal type (see below), an optional duration
 and possibly parameters defined in the package that defines the

Groves, et al. Standards Track [Page 38] RFC 3525 Gateway Control Protocol June 2003

 signal.  This allows a single signal to have some variation in
 meaning, obviating the need to create large numbers of individual
 signals.
 Finally, the optional parameter "notifyCompletion" allows a MGC to
 indicate that it wishes to be notified when the signal finishes
 playout.  The possible cases are that the signal timed out (or
 otherwise completed on its own), that it was interrupted by an event,
 that it was halted when a Signals descriptor was replaced, or that it
 stopped or never started for other reasons.  If the notifyCompletion
 parameter is not included in a Signals descriptor, notification is
 generated only if the signal stopped or was never started for other
 reasons.  For reporting to occur, the signal completion event (see
 E.1.2) must be enabled in the currently active Events descriptor.
 The duration is an integer value that is expressed in hundredths of a
 second.
 There are three types of signals:
  1. on/off - the signal lasts until it is turned off;
  1. timeout - the signal lasts until it is turned off or a specific

period of time elapses;

  1. brief - the signal will stop on its own unless a new Signals

descriptor is applied that causes it to stop; no timeout value is

    needed.
 If a signal of default type other than TO has its type overridden to
 type TO in the Signals descriptor, the duration parameter must be
 present.
 If the signal type is specified in a SignalsDescriptor, it overrides
 the default signal type (see 12.1.4).  If duration is specified for
 an on/off signal, it SHALL be ignored.
 A sequential signal list consists of a signal list identifier and a
 sequence of signals to be played sequentially.  Only the trailing
 element of the sequence of signals in a sequential signal list may be
 an on/off signal.  The duration of a sequential signal list is the
 sum of the durations of the signals it contains.
 Multiple signals and sequential signal lists in the same
 SignalsDescriptor shall be played simultaneously.
 Signals are defined as proceeding from the Termination towards the
 exterior of the Context unless otherwise specified in a package.

Groves, et al. Standards Track [Page 39] RFC 3525 Gateway Control Protocol June 2003

 When the same Signal is applied to multiple Terminations within one
 Transaction, the MG should consider using the same resource to
 generate these Signals.
 Production of a Signal on a Termination is stopped by application of
 a new SignalsDescriptor, or detection of an Event on the Termination
 (see 7.1.9).
 A new SignalsDescriptor replaces any existing SignalsDescriptor.  Any
 signals applied to the Termination not in the replacement descriptor
 shall be stopped, and new signals are applied, except as follows.
 Signals present in the replacement descriptor and containing the
 KeepActive flag shall be continued if they are currently playing and
 have not already completed.  If a replacement signal descriptor
 contains a signal that is not currently playing and contains the
 KeepActive flag, that signal SHALL be ignored.  If the replacement
 descriptor contains a sequential signal list with the same identifier
 as the existing descriptor, then
  1. the signal type and sequence of signals in the sequential signal

list in the replacement descriptor shall be ignored; and

  1. the playing of the signals in the sequential signal list in the

existing descriptor shall not be interrupted.

7.1.12 Audit descriptor

 The Audit descriptor specifies what information is to be audited.
 The Audit descriptor specifies the list of descriptors to be
 returned.  Audit may be used in any command to force the return of
 any descriptor containing the current values of its properties,
 events, signals and statistics even if that descriptor was not
 present in the command, or had no underspecified parameters.
 Possible items in the Audit descriptor are:
    Modem
    Mux
    Events
    Media
    Signals
    ObservedEvents
    DigitMap
    Statistics
    Packages
    EventBuffer

Groves, et al. Standards Track [Page 40] RFC 3525 Gateway Control Protocol June 2003

 Audit may be empty, in which case, no descriptors are returned.  This
 is useful in Subtract, to inhibit return of statistics, especially
 when using wildcard.

7.1.13 ServiceChange descriptor

 The ServiceChangeDescriptor contains the following parameters:
    .  ServiceChangeMethod
    .  ServiceChangeReason
    .  ServiceChangeAddress
    .  ServiceChangeDelay
    .  ServiceChangeProfile
    .  ServiceChangeVersion
    .  ServiceChangeMGCId
    .  TimeStamp
    .  Extension
 See 7.2.8.

7.1.14 DigitMap descriptor

7.1.14.1 DigitMap definition, creation, modification and deletion

 A DigitMap is a dialing plan resident in the Media Gateway used for
 detecting and reporting digit events received on a Termination.  The
 DigitMap descriptor contains a DigitMap name and the DigitMap to be
 assigned.  A digit map may be preloaded into the MG by management
 action and referenced by name in an EventsDescriptor, may be defined
 dynamically and subsequently referenced by name, or the actual
 digitmap itself may be specified in the EventsDescriptor.  It is
 permissible for a digit map completion event within an Events
 descriptor to refer by name to a DigitMap which is defined by a
 DigitMap descriptor within the same command, regardless of the
 transmitted order of the respective descriptors.
 DigitMaps defined in a DigitMapDescriptor can occur in any of the
 standard Termination manipulation Commands of the protocol.  A
 DigitMap, once defined, can be used on all Terminations specified by
 the (possibly wildcarded) TerminationID in such a command.  DigitMaps
 defined on the root Termination are global and can be used on every
 Termination in the MG, provided that a DigitMap with the same name
 has not been defined on the given Termination.  When a DigitMap is
 defined dynamically in a DigitMap descriptor:
  1. A new DigitMap is created by specifying a name that is not yet

defined. The value shall be present.

Groves, et al. Standards Track [Page 41] RFC 3525 Gateway Control Protocol June 2003

  1. A DigitMap value is updated by supplying a new value for a name

that is already defined. Terminations presently using the

    digitmap shall continue to use the old definition; subsequent
    EventsDescriptors specifying the name, including any
    EventsDescriptor in the command containing the DigitMap
    descriptor, shall use the new one.
  1. A DigitMap is deleted by supplying an empty value for a name that

is already defined. Terminations presently using the digitmap

    shall continue to use the old definition.

7.1.14.2 DigitMap Timers

 The collection of digits according to a DigitMap may be protected by
 three timers, viz. a start timer (T), short timer (S), and long timer
 (L).
 1) The start timer (T) is used prior to any digits having been
    dialed.  If the start timer is overridden with the value set to
    zero (T=0), then the start timer shall be disabled.  This implies
    that the MG will wait indefinitely for digits.
 2) If the Media Gateway can determine that at least one more digit is
    needed for a digit string to match any of the allowed patterns in
    the digit map, then the interdigit timer value should be set to a
    long (L) duration (e.g., 16 seconds).
 3) If the digit string has matched one of the patterns in a digit
    map, but it is possible that more digits could be received which
    would cause a match with a different pattern, then instead of
    reporting the match immediately, the MG must apply the short timer
    (S) and wait for more digits.
 The timers are configurable parameters to a DigitMap.  Default values
 of these timers should be provisioned on the MG, but can be
 overridden by values specified within the DigitMap.

7.1.14.3 DigitMap Syntax

 The formal syntax of the digit map is described by the DigitMap rule
 in the formal syntax description of the protocol (see Annex A and
 Annex B).  A DigitMap, according to this syntax, is defined either by
 a string or by a list of strings.  Each string in the list is an
 alternative event sequence, specified either as a sequence of digit
 map symbols or as a regular expression of digit map symbols.  These
 digit map symbols, the digits "0" through "9" and letters "A" through
 a maximum value depending on the signalling system concerned, but
 never exceeding "K", correspond to specified events within a package

Groves, et al. Standards Track [Page 42] RFC 3525 Gateway Control Protocol June 2003

 which has been designated in the Events descriptor on the Termination
 to which the digit map is being applied.  (The mapping between events
 and digit map symbols is defined in the documentation for packages
 associated with channel-associated signalling systems such as DTMF,
 MF, or R2.  Digits "0" through "9" MUST be mapped to the
 corresponding digit events within the signalling system concerned.
 Letters should be allocated in logical fashion, facilitating the use
 of range notation for alternative events.)
 The letter "x" is used as a wildcard, designating any event
 corresponding to symbols in the range "0"-"9".  The string may also
 contain explicit ranges and, more generally, explicit sets of
 symbols, designating alternative events any one of which satisfies
 that position of the digit map.  Finally, the dot symbol "." stands
 for zero or more repetitions of the event selector (event, range of
 events, set of alternative events, or wildcard) that precedes it.  As
 a consequence of the third timing rule above, inter-event timing
 while matching a terminal dot symbol uses the short timer by default.
 In addition to these event symbols, the string may contain "S" and
 "L" inter-event timing specifiers and the "Z" duration modifier.  "S"
 and "L" respectively indicate that the MG should use the short (S)
 timer or the long (L) timer for subsequent events, overriding the
 timing rules described above.  If an explicit timing specifier is in
 effect in one alternative event sequence, but none is given in any
 other candidate alternative, the timer value set by the explicit
 timing specifier must be used.  If all sequences with explicit timing
 controls are dropped from the candidate set, timing reverts to the
 default rules given above.  Finally, if conflicting timing specifiers
 are in effect in different alternative sequences, the long timer
 shall be used.
 A "Z" designates a long duration event: placed in front of the
 symbol(s) designating the event(s) which satisfy a given digit
 position, it indicates that that position is satisfied only if the
 duration of the event exceeds the long-duration threshold.  The value
 of this threshold is assumed to be provisioned in the MG.

7.1.14.4 DigitMap Completion Event

 A digit map is active while the Events descriptor which invoked it is
 active and it has not completed.  A digit map completes when:
  1. a timer has expired; or
  1. an alternative event sequence has been matched and no other

alternative event sequence in the digit map could be matched

    through detection of an additional event (unambiguous match); or

Groves, et al. Standards Track [Page 43] RFC 3525 Gateway Control Protocol June 2003

  1. an event has been detected such that a match to a complete

alternative event sequence of the digit map will be impossible no

    matter what additional events are received.
 Upon completion, a digit map completion event as defined in the
 package providing the events being mapped into the digit map shall be
 generated.  At that point the digit map is deactivated.  Subsequent
 events in the package are processed as per the currently active event
 processing mechanisms.

7.1.14.5 DigitMap Procedures

 Pending completion, successive events shall be processed according to
 the following rules:
 1) The "current dial string", an internal variable, is initially
    empty.  The set of candidate alternative event sequences includes
    all of the alternatives specified in the digit map.
 2) At each step, a timer is set to wait for the next event, based
    either on the default timing rules given above or on explicit
    timing specified in one or more alternative event sequences.  If
    the timer expires and a member of the candidate set of
    alternatives is fully satisfied, a timeout completion with full
    match is reported.  If the timer expires and part or none of any
    candidate alternative is satisfied, a timeout completion with
    partial match is reported.
 3) If an event is detected before the timer expires, it is mapped to
    a digit string symbol and provisionally added to the end of the
    current dial string.  The duration of the event (long or not long)
    is noted if and only if this is relevant in the current symbol
    position (because at least one of the candidate alternative event
    sequences includes the "Z" modifier at this position in the
    sequence).
 4) The current dial string is compared to the candidate alternative
    event sequences.  If and only if a sequence expecting a
    long-duration event at this position is matched (i.e., the event
    had long duration and met the specification for this position),
    then any alternative event sequences not specifying a long
    duration event at this position are discarded, and the current
    dial string is modified by inserting a "Z" in front of the symbol
    representing the latest event.   Any sequence expecting a long-
    duration event at this position but not matching the observed
    event is discarded from the candidate set.  If alternative event
    sequences not specifying a long duration event in the given

Groves, et al. Standards Track [Page 44] RFC 3525 Gateway Control Protocol June 2003

    position remain in the candidate set after application of the
    above rules, the observed event duration is treated as irrelevant
    in assessing matches to them.
 5) If exactly one candidate remains and it has been fully matched, a
    completion event is generated indicating an unambiguous match.  If
    no candidates remain, the latest event is removed from the current
    dial string and a completion event is generated indicating full
    match if one of the candidates from the previous step was fully
    satisfied before the latest event was detected, or partial match
    otherwise.  The event removed from the current dial string will
    then be reported as per the currently active event processing
    mechanisms.
 6) If no completion event is reported out of step 5, processing
    returns to step 2.

7.1.14.6 DigitMap Activation

 A digit map is activated whenever a new Event descriptor is applied
 to the Termination or embedded Event descriptor is activated, and
 that Event descriptor contains a digit map completion event.  The
 digit map completion event contains an eventDM field in the requested
 actions field.  Each new activation of a digit map begins at step 1
 of the above procedure, with a clear current dial string.  Any
 previous contents of the current dial string from an earlier
 activation are lost.
 A digit map completion event that does not contain an eventDM field
 in its requested actions field is considered an error.  Upon receipt
 of such an event in an EventsDescriptor, a MG shall respond with an
 error response, including Error 457 - Missing parameter in signal or
 event.

7.1.14.7 Interaction Of DigitMap and Event Processing

 While the digit map is activated, detection is enabled for all events
 defined in the package containing the specified digit map completion
 event.  Normal event behaviour (e.g., stopping of signals unless the
 digit completion event has the KeepActive flag enabled) continues to
 apply for each such event detected, except that:
  1. the events in the package containing the specified digit map

completion event other than the completion event itself are not

    individually notified and have no side-effects unless separately
    enabled; and

Groves, et al. Standards Track [Page 45] RFC 3525 Gateway Control Protocol June 2003

  1. an event that triggers a partial match completion event is not

recognized and therefore has no side effects until reprocessed

    following the recognition of the digit map completion event.

7.1.14.8 Wildcards

 Note that if a package contains a digit map completion event, then an
 event specification consisting of the package name with a wildcarded
 ItemID (Property Name) will activate a digit map; to that end, the
 event specification must include an eventDM field according to
 section 7.1.14.6.  If the package also contains the digit events
 themselves, this form of event specification will cause the
 individual events to be reported to the MGC as they are detected.

7.1.14.9 Example

 As an example, consider the following dial plan:
 0                      Local operator
 00                     Long-distance operator
 xxxx                   Local extension number (starts with 1-7)
 8xxxxxxx               Local number
 #xxxxxxx               Off-site extension
  • xx Star services
 91xxxxxxxxxx           Long-distance number
 9011 + up to 15 digits International number
 If the DTMF detection package described in E.6 is used to collect the
 dialed digits, then the dialing plan shown above results in the
 following digit map:
  (0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)

7.1.15 Statistics descriptor

 The Statistics Descriptor provides information describing the status
 and usage of a Termination during its existence within a specific
 Context.  There is a set of standard statistics kept for each
 Termination where appropriate (number of octets sent and received for

Groves, et al. Standards Track [Page 46] RFC 3525 Gateway Control Protocol June 2003

 example).  The particular statistical properties that are reported
 for a given Termination are determined by the Packages realized by
 the Termination.  By default, statistics are reported when the
 Termination is Subtracted from the Context.  This behaviour can be
 overridden by including an empty AuditDescriptor in the Subtract
 command.  Statistics may also be returned from the AuditValue
 command, or any Add/Move/Modify command using the Audit descriptor.
 Statistics are cumulative; reporting Statistics does not reset them.
 Statistics are reset when a Termination is Subtracted from a Context.

7.1.16 Packages descriptor

 Used only with the AuditValue command, the PackageDescriptor returns
 a list of Packages realized by the Termination.

7.1.17 ObservedEvents descriptor

 ObservedEvents is supplied with the Notify command to inform the MGC
 of which event(s) were detected.  Used with the AuditValue command,
 the ObservedEventsDescriptor returns events in the event buffer which
 have not been Notified.  ObservedEvents contains the
 RequestIdentifier of the EventsDescriptor that triggered the
 notification, the event(s) detected, optionally the detection time(s)
 and any parameters of the observed event.  Detection times are
 reported with a precision of hundredths of a second.

7.1.18 Topology descriptor

 A Topology descriptor is used to specify flow directions between
 Terminations in a Context.  Contrary to the descriptors in previous
 subclauses, the Topology descriptor applies to a Context instead of a
 Termination.  The default topology of a Context is that each
 Termination's transmission is received by all other Terminations.
 The Topology descriptor is optional to implement.  An MG that does
 not support Topology descriptors, but receives a command containing
 one, returns Error 444 Unsupported or unknown descriptor, and
 optionally includes a string containing the name of the unsupported
 Descriptor ("Topology") in the error text in the error descriptor.
 The Topology descriptor occurs before the commands in an action.  It
 is possible to have an action containing only a Topology descriptor,
 provided that the Context to which the action applies already exists.

Groves, et al. Standards Track [Page 47] RFC 3525 Gateway Control Protocol June 2003

 A Topology descriptor consists of a sequence of triples of the form
 (T1, T2, association).  T1 and T2 specify Terminations within the
 Context, possibly using the ALL or CHOOSE wildcard.  The association
 specifies how media flows between these two Terminations as follows.
  1. (T1, T2, isolate) means that the Terminations matching T2 do not

receive media from the Terminations matching T1, nor vice versa.

  1. (T1, T2, oneway) means that the Terminations that match T2 receive

media from the Terminations matching T1, but not vice versa. In

    this case use of the ALL wildcard such that there are Terminations
    that match both T1 and T2 is not allowed.
  1. (T1, T2, bothway) means that the Terminations matching T2 receive

media from the Terminations matching T1, and vice versa. In this

    case it is allowed to use wildcards such that there are
    Terminations that match both T1 and T2.  However, if there is a
    Termination that matches both, no loopback is introduced.
 CHOOSE wildcards may be used in T1 and T2 as well, under the
 following restrictions:
  1. the action (see clause 8) of which the topology descriptor is part

contains an Add command in which a CHOOSE wildcard is used;

  1. if a CHOOSE wildcard occurs in T1 or T2, then a partial name SHALL

NOT be specified.

 The CHOOSE wildcard in a Topology descriptor matches the
 TerminationID that the MG assigns in the first Add command that uses
 a CHOOSE wildcard in the same action.  An existing Termination that
 matches T1 or T2 in the Context to which a Termination is added, is
 connected to the newly added Termination as specified by the Topology
 descriptor.
 If a termination is not mentioned within a Topology Descriptor, any
 topology associated with it remains unchanged.  If, however, a new
 termination is added into a context its association with the other
 terminations within the context defaults to bothway, unless a
 Topology Descriptor is given to change this (e.g., if T3 is added to
 a context with T1 and T2 with topology (T3, T1, oneway) it will be
 connected bothway to T2).
 Figure 7 and the table following it show some examples of the effect
 of including topology descriptors in actions.  In these examples it
 is assumed that the topology descriptors are applied in sequence.

Groves, et al. Standards Track [Page 48] RFC 3525 Gateway Control Protocol June 2003

   +------------------+  +------------------+  +------------------+
   |      +----+      |  |      +----+      |  |      +----+      |
   |      | T2 |      |  |      | T2 |      |  |      | T2 |      |
   |      +----+      |  |      +----+      |  |      +----+      |
   |       ^  ^       |  |          ^       |  |          ^       |
   |       |  |       |  |          |       |  |          |       |
   |    +--+  +--+    |  |          +---+   |  |          +--+    |
   |    |        |    |  |              |   |  |             |    |
   |    v        v    |  |              v   |  |             |    |
   | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
   | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |
   | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
   +------------------+  +------------------+  +------------------+
   1. No Topology Desc.   2. T1, T2, Isolate    3. T3, T2, Oneway
   +------------------+  +------------------+  +------------------+
   |      +----+      |  |      +----+      |  |      +----+      |
   |      | T2 |      |  |      | T2 |      |  |      | T2 |      |
   |      +----+      |  |      +----+      |  |      +----+      |
   |          |       |  |          ^       |  |       ^  ^       |
   |          |       |  |          |       |  |       |  |       |
   |          +--+    |  |          +---+   |  |    +--+  +--+    |
   |             |    |  |              |   |  |    |        |    |
   |             v    |  |              v   |  |    v        v    |
   | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
   | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |
   | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
   +------------------+  +------------------+  +------------------+
   4. T2, T3 oneway      5. T2, T3 bothway     6. T1, T2 bothway
   Note: the direction of the arrow indicates the direction of flow.
                     Figure 7: Example topologies
 Topology Description
 1 No topology descriptors    When no topology descriptors are
                              included, all Terminations have a
                              bothway connection to all other
                              Terminations.
 2 T1, T2 Isolate             Removes the connection between T1 and
                              T2.  T3 has a bothway connection with
                              both T1 and T2.  T1 and T2 have bothway
                              connection to T3.

Groves, et al. Standards Track [Page 49] RFC 3525 Gateway Control Protocol June 2003

 3 T3, T2 oneway              A oneway connection from T3 to T2 (i.e.,
                              T2 receives media flow from T3).  A
                              bothway connection between T1 and T3.
 4 T2, T3 oneway              A oneway connection between T2 to T3.
                              T1 and T3 remain bothway connected.
 5 T2, T3 bothway             T2 is bothway connected to T3.  This
                              results in the same as 2.
 6 T1, T2 bothway (T2, T3     All Terminations have a bothway
   bothway and T1, T3         connection to all other Terminations.
   bothway may be implied or
   explicit).
 A oneway connection must be implemented in such a way that the other
 Terminations in the Context are not aware of the change in topology.

7.1.19 Error Descriptor

 If a responder encounters an error when processing a transaction
 request, it must include an error descriptor in its response.  A
 Notify request may contain an error descriptor as well.
 An error descriptor consists of an IANA-registered error code,
 optionally accompanied by an error text.  H.248.8 contains a list of
 valid error codes and error descriptions.
 An error descriptor shall be specified at the "deepest level" that is
 semantically appropriate for the error being described and that is
 possible given any parsing problems with the original request.  An
 error descriptor may refer to a syntactical construct other than
 where it appears.  For example, Error descriptor 422 - Syntax Error
 in Action, could appear within a command even though it refers to the
 larger construct - the action - and not the particular command within
 which it appears.

7.2 Command Application Programming Interface

 Following is an Application Programming Interface (API) describing
 the Commands of the protocol.  This API is shown to illustrate the
 Commands and their parameters and is not intended to specify
 implementation (e.g., via use of blocking function calls).  It
 describes the input parameters in parentheses after the command name
 and the return values in front of the Command.  This is only for
 descriptive purposes; the actual Command syntax and encoding are

Groves, et al. Standards Track [Page 50] RFC 3525 Gateway Control Protocol June 2003

 specified in later subclauses.  The order of parameters to commands
 is not fixed.  Descriptors may appear as parameters to commands in
 any order.  The descriptors SHALL be processed in the order in which
 they appear.
 Any reply to a command may contain an error descriptor; the API does
 not specifically show this.
 All parameters enclosed by square brackets ([. . .]) are considered
 optional.

7.2.1 Add

 The Add Command adds a Termination to a Context.
   TerminationID
   [,MediaDescriptor]
   [,ModemDescriptor]
   [,MuxDescriptor]
   [,EventsDescriptor]
   [,SignalsDescriptor]
   [,DigitMapDescriptor]
   [,ObservedEventsDescriptor]
   [,EventBufferDescriptor]
   [,StatisticsDescriptor]
   [,PackagesDescriptor]
     Add( TerminationID
      [, MediaDescriptor]
      [, ModemDescriptor]
      [, MuxDescriptor]
      [, EventsDescriptor]
      [, EventBufferDescriptor]
      [, SignalsDescriptor]
      [, DigitMapDescriptor]
      [, AuditDescriptor]
      )
 The TerminationID specifies the Termination to be added to the
 Context.  The Termination is either created, or taken from the null
 Context.  If a CHOOSE wildcard is used in the TerminationID, the
 selected TerminationID will be returned.  Wildcards may be used in an
 Add, but such usage would be unusual.  If the wildcard matches more
 than one TerminationID, all possible matches are attempted, with
 results reported for each one.  The order of attempts when multiple
 TerminationIDs match is not specified.
 The optional MediaDescriptor describes all media streams.

Groves, et al. Standards Track [Page 51] RFC 3525 Gateway Control Protocol June 2003

 The optional ModemDescriptor and MuxDescriptor specify a modem and
 multiplexer if applicable.  For convenience, if a Multiplex
 descriptor is present in an Add command and lists any Terminations
 that are not currently in the Context, such Terminations are added to
 the Context as if individual Add commands listing the Terminations
 were invoked. If an error occurs on such an implied Add, error 471 -
 Implied Add for Multiplex failure shall be returned and further
 processing of the command shall cease.
 The EventsDescriptor parameter is optional.  If present, it provides
 the list of events that should be detected on the Termination.
 The EventBufferDescriptor parameter is optional.  If present, it
 provides the list of events that the MG is requested to detect and
 buffer when EventBufferControl equals LockStep.
 The SignalsDescriptor parameter is optional.  If present, it provides
 the list of signals that should be applied to the Termination.
 The DigitMapDescriptor parameter is optional.  If present, it defines
 a DigitMap definition that may be used in an EventsDescriptor.
 The AuditDescriptor is optional.  If present, the command will return
 descriptors as specified in the AuditDescriptor.
 All descriptors that can be modified could be returned by MG if a
 parameter was underspecified or overspecified.  ObservedEvents,
 Statistics, and Packages, and the EventBuffer descriptors are
 returned only if requested in the AuditDescriptor.
 Add SHALL NOT be used on a Termination with a serviceState of
 "OutofService".

7.2.2 Modify

 The Modify Command modifies the properties of a Termination.
   TerminationID
   [,MediaDescriptor]
   [,ModemDescriptor]
   [,MuxDescriptor]
   [,EventsDescriptor]
   [,SignalsDescriptor]
   [,DigitMapDescriptor]
   [,ObservedEventsDescriptor]
   [,EventBufferDescriptor]
   [,StatisticsDescriptor]
   [,PackagesDescriptor]

Groves, et al. Standards Track [Page 52] RFC 3525 Gateway Control Protocol June 2003

    Modify( TerminationID
       [, MediaDescriptor]
       [, ModemDescriptor]
       [, MuxDescriptor]
       [, EventsDescriptor]
       [, EventBufferDescriptor]
       [, SignalsDescriptor]
       [, DigitMapDescriptor]
       [, AuditDescriptor]
       )
 The TerminationID may be specific if a single Termination in the
 Context is to be modified.  Use of wildcards in the TerminationID may
 be appropriate for some operations.  If the wildcard matches more
 than one TerminationID, all possible matches are attempted, with
 results reported for each one.  The order of attempts when multiple
 TerminationIDs match is not specified.  The CHOOSE option is an
 error, as the Modify command may only be used on existing
 Terminations.
 For convenience, if a Multiplex Descriptor is present in a Modify
 command, then:
  1. if the new Multiplex Descriptor lists any Terminations that are

not currently in the Context, such Terminations are added to the

    context as if individual commands listing the Terminations were
    invoked.
  1. if any Terminations listed previously in the Multiplex Descriptor

are no longer present in the new Multiplex Descriptor, they are

    subtracted from the context as if individual Subtract commands
    listing the Terminations were invoked.
 The remaining parameters to Modify are the same as those to Add.
 Possible return values are the same as those to Add.

7.2.3 Subtract

 The Subtract Command disconnects a Termination from its Context and
 returns statistics on the Termination's participation in the Context.
   TerminationID
   [,MediaDescriptor]
   [,ModemDescriptor]
   [,MuxDescriptor]
   [,EventsDescriptor]
   [,SignalsDescriptor]
   [,DigitMapDescriptor]

Groves, et al. Standards Track [Page 53] RFC 3525 Gateway Control Protocol June 2003

   [,ObservedEventsDescriptor]
   [,EventBufferDescriptor]
   [,StatisticsDescriptor]
   [,PackagesDescriptor]
    Subtract(TerminationID
       [, AuditDescriptor]
       )
 TerminationID in the input parameters represents the Termination that
 is being subtracted.  The TerminationID may be specific or may be a
 wildcard value indicating that all (or a set of related) Terminations
 in the Context of the Subtract Command are to be subtracted.  If the
 wildcard matches more than one TerminationID, all possible matches
 are attempted, with results reported for each one.  The order of
 attempts when multiple TerminationIDs match is not specified.
 The use of CHOOSE in the TerminationID is an error, as the Subtract
 command may only be used on existing Terminations.
 ALL may be used as the ContextID as well as the TerminationId in a
 Subtract, which would have the effect of deleting all Contexts,
 deleting all ephemeral Terminations, and returning all physical
 Terminations to Null Context.  Subtract of a termination from the
 Null Context is not allowed.
 For convenience, if a multiplexing Termination is the object of a
 Subtract command, then any bearer Terminations listed in its
 Multiplex Descriptor are subtracted from the context as if individual
 Subtract commands listing the Terminations were invoked.
 By default, the Statistics parameter is returned to report
 information collected on the Termination or Terminations specified in
 the Command.  The information reported applies to the Termination's
 or Terminations' existence in the Context from which it or they are
 being subtracted.
 The AuditDescriptor is optional.  If present, the command will return
 only those descriptors as specified in the AuditDescriptor, which may
 be empty.  If omitted, the Statistics descriptor is returned, by
 default.  Possible return values are the same as those to Add.
 When a provisioned Termination is Subtracted from a Context, its
 property values shall revert to:
  1. the default value, if specified for the property and not

overridden by provisioning;

  1. otherwise, the provisioned value.

Groves, et al. Standards Track [Page 54] RFC 3525 Gateway Control Protocol June 2003

7.2.4 Move

 The Move Command moves a Termination to another Context from its
 current Context in one atomic operation.  The Move command is the
 only command that refers to a Termination in a Context different from
 that to which the command is applied.  The Move command shall not be
 used to move Terminations to or from the null Context.
   TerminationID
   [,MediaDescriptor]
   [,ModemDescriptor]
   [,MuxDescriptor]
   [,EventsDescriptor]
   [,SignalsDescriptor]
   [,DigitMapDescriptor]
   [,ObservedEventsDescriptor]
   [,EventBufferDescriptor]
   [,StatisticsDescriptor]
   [,PackagesDescriptor]
    Move( TerminationID
       [, MediaDescriptor]
       [, ModemDescriptor]
       [, MuxDescriptor]
       [, EventsDescriptor]
       [, EventBufferDescriptor]
       [, SignalsDescriptor]
       [, DigitMapDescriptor]
       [, AuditDescriptor]
       )
 The TerminationID specifies the Termination to be moved.  It may be
 wildcarded, but CHOOSE shall not be used in the TerminationID.  If
 the wildcard matches more than one TerminationID, all possible
 matches are attempted, with results reported for each one.  The order
 of attempts when multiple TerminationIDs match is not specified.  The
 Context to which the Termination is moved is indicated by the target
 ContextId in the Action.  If the last remaining Termination is moved
 out of a Context, the Context is deleted.
 The Move command does not affect the properties of the Termination on
 which it operates, except those properties explicitly modified by
 descriptors included in the Move command.  The AuditDescriptor with
 the Statistics option, for example, would return statistics on the
 Termination just prior to the Move.  Possible descriptors returned
 from Move are the same as for Add.

Groves, et al. Standards Track [Page 55] RFC 3525 Gateway Control Protocol June 2003

 For convenience, if a multiplexing Termination is the object of a
 Move command, then any bearer Terminations listed in its Multiplex
 Descriptor are also moved as if individual Move commands listing the
 Terminations were invoked.
 Move SHALL NOT be used on a Termination with a serviceState of
 "OutofService".

7.2.5 AuditValue

 The AuditValue Command returns the current values of properties,
 events, signals and statistics associated with Terminations.
 TerminationID
 [,MediaDescriptor]
 [,ModemDescriptor]
 [,MuxDescriptor]
 [,EventsDescriptor]
 [,SignalsDescriptor]
 [,DigitMapDescriptor]
 [,ObservedEventsDescriptor]
 [,EventBufferDescriptor]
 [,StatisticsDescriptor]
 [,PackagesDescriptor]
   AuditValue(TerminationID,
    AuditDescriptor
    )
 TerminationID may be specific or wildcarded.  If the wildcard matches
 more than one TerminationID, all possible matches are attempted, with
 results reported for each one.  The order of attempts when multiple
 TerminationIDs match is not specified.  If a wildcarded response is
 requested, only one command return is generated, with the contents
 containing the union of the values of all Terminations matching the
 wildcard.  This convention may reduce the volume of data required to
 audit a group of Terminations.  Use of CHOOSE is an error.
 The appropriate descriptors, with the current values for the
 Termination, are returned from AuditValue.  Values appearing in
 multiple instances of a descriptor are defined to be alternate values
 supported, with each parameter in a descriptor considered
 independent.
 ObservedEvents returns a list of events in the EventBuffer.  If the
 ObservedEventsDescriptor is audited while a DigitMap is active, the
 returned ObservedEvents descriptor also includes a digit map
 completion event that shows the current dial string but does not show
 a Termination method.

Groves, et al. Standards Track [Page 56] RFC 3525 Gateway Control Protocol June 2003

 EventBuffer returns the set of events and associated parameter values
 currently enabled in the EventBufferDescriptor.  PackagesDescriptor
 returns a list of packages realized by the Termination.
 DigitMapDescriptor returns the name or value of the current DigitMap
 for the Termination.  DigitMap requested in an AuditValue command
 with TerminationID ALL returns all DigitMaps in the gateway.
 Statistics returns the current values of all statistics being kept on
 the Termination.   Specifying an empty Audit descriptor results in
 only the TerminationID being returned.  This may be useful to get a
 list of TerminationIDs when used with wildcard.  Annexes A and B
 provide a special syntax for presenting such a list in condensed
 form, such that the AuditValue command tag does not have to be
 repeated for each TerminationID.
 AuditValue results depend on the Context, viz. specific, null, or
 wildcarded.  (Note that ContextID ALL does not include the null
 Context.)  The TerminationID may be specific, or wildcarded.
 The following are examples of what is returned in case the context
 and/or the termination is wildcarded and a wildcarded response has
 been specified.
 Assume that the gateway has 4 terminations: t1/1, t1/2, t2/1 and
 t2/2.  Assume that terminations t1/* have implemented packages aaa
 and bbb and that terminations t2/* have implemented packages ccc and
 ddd.  Assume that Context 1 has t1/1 and t2/1 in it and that Context
 2 has t1/2 and t2/2 in it.
 The command:
   Context=1{AuditValue=t1/1{Audit{Packages}}}
 Returns:
   Context=1{AuditValue=t1/1{Packages{aaa,bbb}}}
 The command:
   Context=*{AuditValue=t2/*{Audit{Packages}}}
 Returns:
   Context=1{AuditValue=t2/1{Packages{ccc,ddd}}},
   Context=2{AuditValue=t2/2{Packages{ccc,ddd}}}
 The command:
   Context=*{W-AuditValue=t1/*{Audit{Packages}}}

Groves, et al. Standards Track [Page 57] RFC 3525 Gateway Control Protocol June 2003

 Returns:
   Context=*{W-AuditValue=t1/*{Packages{aaa,bbb}}}
 Note: A wildcard response may also be used for other commands such as
 Subtract.
 The following illustrates other information that can be obtained with
 the AuditValue Command:
 ContextID TerminationID Information Obtained
 Specific  wildcard      Audit of matching Terminations in a Context
 Specific  specific      Audit of a single Termination in a Context
 Null      Root          Audit of Media Gateway state and events
 Null      wildcard      Audit of all matching Terminations in the
                          null Context
 Null      specific      Audit of a single Termination outside of any
                          Context
 All       wildcard      Audit of all matching Terminations and the
                          Context to which they are associated
 All       Root          List of all ContextIds (the ContextID list
                          should be returned by using multiple action
                          replies, each containing a ContextID from
                          the list)
 All       Specific      (Non-null) ContextID in which the
                          Termination currently exists

Groves, et al. Standards Track [Page 58] RFC 3525 Gateway Control Protocol June 2003

7.2.6 AuditCapabilities

 The AuditCapabilities Command returns the possible values of
 properties, events, signals and statistics associated with
 Terminations.
   TerminationID
   [,MediaDescriptor]
   [,ModemDescriptor]
   [,MuxDescriptor]
   [,EventsDescriptor]
   [,SignalsDescriptor]
   [,ObservedEventsDescriptor]
   [,EventBufferDescriptor]
   [,StatisticsDescriptor]
    AuditCapabilities(TerminationID,
       AuditDescriptor
       )
 The appropriate descriptors, with the possible values for the
 Termination are returned from AuditCapabilities.  Descriptors may be
 repeated where there are multiple possible values.  If a wildcarded
 response is requested, only one command return is generated, with the
 contents containing the union of the values of all Terminations
 matching the wildcard.  This convention may reduce the volume of data
 required to audit a group of Terminations.
 Interpretation of what capabilities are requested for various values
 of ContextID and TerminationID is the same as in AuditValue.
 The EventsDescriptor returns the list of possible events on the
 Termination together with the list of all possible values for the
 EventsDescriptor Parameters.  EventBufferDescriptor returns the same
 information as EventsDescriptor.  The SignalsDescriptor returns the
 list of possible signals that could be applied to the Termination
 together with the list of all possible values for the Signals
 Parameters.  StatisticsDescriptor returns the names of the statistics
 being kept on the termination.  ObservedEventsDescriptor returns the
 names of active events on the Termination.  DigitMap and Packages are
 not legal in AuditCapability.

Groves, et al. Standards Track [Page 59] RFC 3525 Gateway Control Protocol June 2003

 The following illustrates other information that can be obtained with
 the AuditCapabilties Command:
 ContextID TerminationID Information Obtained
 Specific  wildcard      Audit of matching Terminations in a Context
 Specific  specific      Audit of a single Termination in a Context
 Null      Root          Audit of MG state and events
 Null      wildcard      Audit of all matching Terminations in the
                          Null Context
 Null      specific      Audit of a single Termination outside of any
                          Context
 All       wildcard      Audit of all matching Terminations and the
                          Context to which they are associated
 All       Root          Same as for AuditValue
 All       Specific      Same as for AuditValue

7.2.7 Notify

 The Notify Command allows the Media Gateway to notify the Media
 Gateway Controller of events occurring within the Media Gateway.
   TerminationID
    Notify(TerminationID,
       ObservedEventsDescriptor,
       [ErrorDescriptor]
       )
 The TerminationID parameter specifies the Termination issuing the
 Notify Command.  The TerminationID shall be a fully qualified name.
 The ObservedEventsDescriptor contains the RequestID and a list of
 events that the Media Gateway detected in the order that they were
 detected.  Each event in the list is accompanied by parameters
 associated with the event and optionally an indication of the time
 that the event was detected.  Procedures for sending Notify commands
 with RequestID equal to 0 are for further study.
 Notify Commands with RequestID not equal to 0 shall occur only as the
 result of detection of an event specified by an Events descriptor
 which is active on the Termination concerned.

Groves, et al. Standards Track [Page 60] RFC 3525 Gateway Control Protocol June 2003

 The RequestID returns the RequestID parameter of the EventsDescriptor
 that triggered the Notify Command.  It is used to correlate the
 notification with the request that triggered it.  The events in the
 list must have been requested via the triggering EventsDescriptor or
 embedded events descriptor unless the RequestID is 0 (which is for
 further study).
 The ErrorDescriptor may be sent in the Notify Command as a result of
 Error 518 - Event buffer full.

7.2.8 ServiceChange

 The ServiceChange Command allows the Media Gateway to notify the
 Media Gateway Controller that a Termination or group of Terminations
 is about to be taken out of service or has just been returned to
 service.  The Media Gateway Controller may indicate that
 Termination(s) shall be taken out of or returned to service.   The
 Media Gateway may notify the MGC that the capability of a Termination
 has changed.  It also allows a MGC to hand over control of a MG to
 another MGC.
 TerminationID,
   [ServiceChangeDescriptor]
    ServiceChange ( TerminationID,
       ServiceChangeDescriptor
       )
 The TerminationID parameter specifies the Termination(s) that are
 taken out of or returned to service.  Wildcarding of Termination
 names is permitted, with the exception that the CHOOSE mechanism
 shall not be used.  Use of the "Root" TerminationID indicates a
 ServiceChange affecting the entire Media Gateway.
 The ServiceChangeDescriptor contains the following parameters as
 required:
  1. ServiceChangeMethod
  2. ServiceChangeReason
  3. ServiceChangeDelay
  4. ServiceChangeAddress
  5. ServiceChangeProfile
  6. ServiceChangeVersion
  7. ServiceChangeMgcId
  8. TimeStamp

Groves, et al. Standards Track [Page 61] RFC 3525 Gateway Control Protocol June 2003

 The ServiceChangeMethod parameter specifies the type of ServiceChange
 that will or has occurred:
 1) Graceful - indicates that the specified Terminations will be taken
    out of service after the specified ServiceChangeDelay; established
    connections are not yet affected, but the Media Gateway Controller
    should refrain from establishing new connections and should
    attempt to gracefully tear down existing connections on the
    Termination(s) affected by the serviceChange command.  The MG
    should set Termination serviceState at the expiry of
    ServiceChangeDelay or the removal of the Termination from an
    active Context (whichever is first), to "out of service".
 2) Forced - indicates that the specified Terminations were taken
    abruptly out of service and any established connections associated
    with them may be lost.  For non-Root terminations, the MGC is
    responsible for cleaning up the Context (if any) with which the
    failed Termination is associated.  At a minimum the Termination
    shall be subtracted from the Context.  The Termination
    serviceState should be "out of service".  For the root
    termination, the MGC can assume that all connections are lost on
    the MG and thus can consider that all the terminations have been
    subtracted.
 3) Restart - indicates that service will be restored on the specified
    Terminations after expiration of the ServiceChangeDelay.  The
    serviceState should be set to "inService" upon expiry of
    ServiceChangeDelay.
 4) Disconnected - always applied with the Root TerminationID,
    indicates that the MG lost communication with the MGC, but it was
    subsequently restored to the same MGC (possibly after trying other
    MGCs on a pre-provisioned list).  Since MG state may have changed,
    the MGC may wish to use the Audit command to resynchronize its
    state with the MG's.
 5) Handoff - sent from the MGC to the MG, this reason indicates that
    the MGC is going out of service and a new MGC association must be
    established.  Sent from the MG to the MGC, this indicates that the
    MG is attempting to establish a new association in accordance with
    a Handoff received from the MGC with which it was previously
    associated.
 6) Failover - sent from MG to MGC to indicate the primary MG is out
    of service and a secondary MG is taking over.  This serviceChange
    method is also sent from the MG to the MGC when the MG detects
    that MGC has failed.

Groves, et al. Standards Track [Page 62] RFC 3525 Gateway Control Protocol June 2003

 7) Another value whose meaning is mutually understood between the MG
    and the MGC.
 The ServiceChangeReason parameter specifies the reason why the
 ServiceChange has or will occur.  It consists of an alphanumeric
 token (IANA registered) and, optionally, an explanatory string.
 The optional ServiceChangeAddress parameter specifies the address
 (e.g., IP port number for IP networks) to be used for subsequent
 communications.  It can be specified in the input parameter
 descriptor or the returned result descriptor.  ServiceChangeAddress
 and ServiceChangeMgcId parameters must not both be present in the
 ServiceChangeDescriptor or the ServiceChangeResultDescriptor.  The
 ServiceChangeAddress provides an address to be used within the
 Context of the association currently being negotiated, while the
 ServiceChangeMgcId provides an alternate address where the MG should
 seek to establish another association.  Note that the use of
 ServiceChangeAddress is not encouraged.  MGCs and MGs must be able to
 cope with the ServiceChangeAddress being either a full address or
 just a port number in the case of TCP transports.
 The optional ServiceChangeDelay parameter is expressed in seconds.
 If the delay is absent or set to zero, the delay value should be
 considered to be null.  In the case of a "graceful"
 ServiceChangeMethod, a null delay indicates that the Media Gateway
 Controller should wait for the natural removal of existing
 connections and should not establish new connections.  For "graceful"
 only, a null delay means the MG must not set serviceState "out of
 service" until the Termination is in the null Context.
 The optional ServiceChangeProfile parameter specifies the Profile (if
 any) of the protocol supported.  The ServiceChangeProfile includes
 the version of the profile supported.
 The optional ServiceChangeVersion parameter contains the protocol
 version and is used if protocol version negotiation occurs (see
 11.3).
 The optional TimeStamp parameter specifies the actual time as kept by
 the sender.  As such, it is not necessarily absolute time according
 to, for example, a local time zone - it merely establishes an
 arbitrary starting time against which all future timestamps
 transmitted by a sender during this association shall be compared.
 It can be used by the responder to determine how its notion of time
 differs from that of its correspondent.  TimeStamp is sent with a
 precision of hundredths of a second.

Groves, et al. Standards Track [Page 63] RFC 3525 Gateway Control Protocol June 2003

 The optional Extension parameter may contain any value whose meaning
 is mutually understood by the MG and MGC.
 A ServiceChange Command specifying the "Root" for the TerminationID
 and ServiceChangeMethod equal to Restart is a registration command by
 which a Media Gateway announces its existence to the Media Gateway
 Controller.  The Media Gateway may also announce a registration
 command by specifying the "Root" for the TerminationID and
 ServiceChangeMethod equal to Failover when the MG detects MGC
 failures.  The Media Gateway is expected to be provisioned with the
 name of one primary and optionally some number of alternate Media
 Gateway Controllers.  Acknowledgement of the ServiceChange Command
 completes the registration process, except when the MGC has returned
 an alternative ServiceChangeMgcId as described in the following
 paragraph.  The MG may specify the transport ServiceChangeAddress to
 be used by the MGC for sending messages in the ServiceChangeAddress
 parameter in the input ServiceChangeDescriptor.  The MG may specify
 an address in the ServiceChangeAddress parameter of the ServiceChange
 request, and the MGC may also do so in the ServiceChange reply.  In
 either case, the recipient must use the supplied address as the
 destination for all subsequent transaction requests within the
 association.  At the same time, as indicated in clause 9, transaction
 replies and pending indications must be sent to the address from
 which the corresponding requests originated.  This must be done even
 if it implies extra messaging because commands and responses cannot
 be packed together.  The TimeStamp parameter shall be sent with a
 registration command and its response.
 The Media Gateway Controller may return a ServiceChangeMgcId
 parameter that describes the Media Gateway Controller that should
 preferably be contacted for further service by the Media Gateway.  In
 this case the Media Gateway shall reissue the ServiceChange command
 to the new Media Gateway Controller.  The MGC specified in a
 ServiceChangeMgcId, if provided, shall be contacted before any
 further alternate MGCs.  On a HandOff message from MGC to MG, the
 ServiceChangeMgcId is the new MGC that will take over from the
 current MGC.
 The return from ServiceChange is empty except when the Root
 terminationID is used.  In that case it includes the following
 parameters as required:
  1. ServiceChangeAddress, if the responding MGC wishes to specify a

new destination for messages from the MG for the remainder of the

    association;
  1. ServiceChangeMgcId, if the responding MGC does not wish to sustain

an association with the MG;

Groves, et al. Standards Track [Page 64] RFC 3525 Gateway Control Protocol June 2003

  1. ServiceChangeProfile, if the responder wishes to negotiate the

profile to be used for the association;

  1. ServiceChangeVersion, if the responder wishes to negotiate the

version of the protocol to be used for the association.

 The following ServiceChangeReasons are defined.  This list may be
 extended by an IANA registration as outlined in 13.3.
    900 Service Restored
    901 Cold Boot
    902 Warm Boot
    903 MGC Directed Change
    904 Termination malfunctioning
    905 Termination taken out of service
    906 Loss of lower layer connectivity (e.g., downstream sync)
    907 Transmission Failure
    908 MG Impending Failure
    909 MGC Impending Failure
    910 Media Capability Failure
    911 Modem Capability Failure
    912 Mux Capability Failure
    913 Signal Capability Failure
    914 Event Capability Failure
    915 State Loss

7.2.9 Manipulating and Auditing Context Attributes

 The commands of the protocol as discussed in the preceding subclauses
 apply to Terminations.  This subclause specifies how Contexts are
 manipulated and audited.
 Commands are grouped into actions (see clause 8).  An action applies
 to one Context.  In addition to commands, an action may contain
 Context manipulation and auditing instructions.
 An action request sent to a MG may include a request to audit
 attributes of a Context.  An action may also include a request to
 change the attributes of a Context.
 The Context properties that may be included in an action reply are
 used to return information to a MGC.  This can be information
 requested by an audit of Context attributes or details of the effect
 of manipulation of a Context.

Groves, et al. Standards Track [Page 65] RFC 3525 Gateway Control Protocol June 2003

 If a MG receives an action which contains both a request to audit
 context attributes and a request to manipulate those attributes, the
 response SHALL include the values of the attributes after processing
 the manipulation request.

7.2.10 Generic Command Syntax

 The protocol can be encoded in a binary format or in a text format.
 MGCs should support both encoding formats.  MGs may support both
 formats.
 The protocol syntax for the binary format of the protocol is defined
 in Annex A.  Annex C specifies the encoding of the Local and Remote
 descriptors for use with the binary format.
 A complete ABNF of the text encoding of the protocol per RFC 2234 is
 given in Annex B.  SDP is used as the encoding of the Local and
 Remote descriptors for use with the text encoding as modified in
 7.1.8.

7.3 Command Error Codes

 Errors consist of an IANA registered error code and an explanatory
 string.  Sending the explanatory string is optional.  Implementations
 are encouraged to append diagnostic information to the end of the
 string.
 When a MG reports an error to a MGC, it does so in an error
 descriptor.  An error descriptor consists of an error code and
 optionally the associated explanatory string.
 H.248.8 contains the error codes supported by Recommendations in the
 H.248 sub-series.

8 Transactions

 Commands between the Media Gateway Controller and the Media Gateway
 are grouped into Transactions, each of which is identified by a
 TransactionID.  Transactions consist of one or more Actions.  An
 Action consists of a non-empty series of Commands, Context property
 modifications, or Context property audits that are limited to
 operating within a single Context.  Consequently, each Action
 typically specifies a ContextID.  However, there are two
 circumstances where a specific ContextID is not provided with an
 Action.  One is the case of modification of a Termination outside of
 a Context.  The other is where the controller requests the gateway to
 create a new Context.  Figure 8 is a graphic representation of the
 Transaction, Action and Command relationships.

Groves, et al. Standards Track [Page 66] RFC 3525 Gateway Control Protocol June 2003

    +----------------------------------------------------------+
    | Transaction x                                            |
    |  +----------------------------------------------------+  |
    |  | Action 1                                           |  |
    |  | +---------+  +---------+  +---------+  +---------+ |  |
    |  | | Command |  | Command |  | Command |  | Command | |  |
    |  | |    1    |  |    2    |  |    3    |  |    4    | |  |
    |  | +---------+  +---------+  +---------+  +---------+ |  |
    |  +----------------------------------------------------+  |
    |                                                          |
    |  +----------------------------------------------------+  |
    |  | Action 2                                           |  |
    |  | +---------+                                        |  |
    |  | | Command |                                        |  |
    |  | |    1    |                                        |  |
    |  | +---------+                                        |  |
    |  +----------------------------------------------------+  |
    |                                                          |
    |  +----------------------------------------------------+  |
    |  | Action 3                                           |  |
    |  | +---------+  +---------+  +---------+              |  |
    |  | | Command |  | Command |  | Command |              |  |
    |  | |    1    |  |    2    |  |    3    |              |  |
    |  | +---------+  +---------+  +---------+              |  |
    |  +----------------------------------------------------+  |
    +----------------------------------------------------------+
             Figure 8: Transactions, Actions and Commands
 Transactions are presented as TransactionRequests.  Corresponding
 responses to a TransactionRequest are received in a single reply,
 possibly preceded by a number of TransactionPending messages (see
 8.2.3).
 Transactions guarantee ordered Command processing.  That is, Commands
 within a Transaction are executed sequentially.  Ordering of
 Transactions is NOT guaranteed - transactions may be executed in any
 order, or simultaneously.
 At the first failing Command in a Transaction, processing of the
 remaining Commands in that Transaction stops.  If a command contains
 a wildcarded TerminationID, the command is attempted with each of the
 actual TerminationIDs matching the wildcard.  A response within the
 TransactionReply is included for each matching TerminationID, even if
 one or more instances generated an error.  If any TerminationID
 matching a wildcard results in an error when executed, any commands
 following the wildcarded command are not attempted.

Groves, et al. Standards Track [Page 67] RFC 3525 Gateway Control Protocol June 2003

 Commands may be marked as "Optional" which can override this
 behaviour - if a command marked as Optional results in an error,
 subsequent commands in the Transaction will be executed.  If a
 command fails, the MG shall as far as possible restore the state that
 existed prior to the attempted execution of the command before
 continuing with command processing.
 A TransactionReply includes the results for all of the Commands in
 the corresponding TransactionRequest.  The TransactionReply includes
 the return values for the Commands that were executed successfully,
 and the Command and error descriptor for any Command that failed.
 TransactionPending is used to periodically notify the receiver that a
 Transaction has not completed yet, but is actively being processed.
 Applications SHOULD implement an application level timer per
 transaction.  Expiration of the timer should cause a retransmission
 of the request.  Receipt of a Reply should cancel the timer.  Receipt
 of Pending should restart the timer.

8.1 Common parameters

8.1.1 Transaction Identifiers

 Transactions are identified by a TransactionID, which is assigned by
 sender and is unique within the scope of the sender.  A response
 containing an error descriptor to indicate that the TransactionID is
 missing in a request shall use TransactionID 0 in the corresponding
 TransactionReply.

8.1.2 Context Identifiers

 Contexts are identified by a ContextID, which is assigned by the
 Media Gateway and is unique within the scope of the Media Gateway.
 The Media Gateway Controller shall use the ContextID supplied by the
 Media Gateway in all subsequent Transactions relating to that
 Context.  The protocol makes reference to a distinguished value that
 may be used by the Media Gateway Controller when referring to a
 Termination that is currently not associated with a Context, namely
 the null ContextID.
 The CHOOSE wildcard is used to request that the Media Gateway create
 a new Context.
 The MGC may use the ALL wildcard to address all Contexts on the MG.
 The null Context is not included when the ALL wildcard is used.

Groves, et al. Standards Track [Page 68] RFC 3525 Gateway Control Protocol June 2003

 The MGC shall not use partially specified ContextIDs containing the
 CHOOSE or ALL wildcards.

8.2 Transaction Application Programming Interface

 Following is an Application Programming Interface (API) describing
 the Transactions of the protocol.  This API is shown to illustrate
 the Transactions and their parameters and is not intended to specify
 implementation (e.g., via use of blocking function calls).  It will
 describe the input parameters and return values expected to be used
 by the various Transactions of the protocol from a very high level.
 Transaction syntax and encodings are specified in later subclauses.

8.2.1 TransactionRequest

 The TransactionRequest is invoked by the sender.  There is one
 Transaction per request invocation.  A request contains one or more
 Actions, each of which specifies its target Context and one or more
 Commands per Context.
   TransactionRequest(TransactionId {
       ContextID {Command ... Command},
          . . .
       ContextID {Command ... Command } })
 The TransactionID parameter must specify a value for later
 correlation with the TransactionReply or TransactionPending response
 from the receiver.
 The ContextID parameter must specify a value to pertain to all
 Commands that follow up to either the next specification of a
 ContextID parameter or the end of the TransactionRequest, whichever
 comes first.
 The Command parameter represents one of the Commands mentioned in 7.2
 (Command Application Programming Interface).

8.2.2 TransactionReply

 The TransactionReply is invoked by the receiver.  There is one reply
 invocation per transaction.  A reply contains one or more Actions,
 each of which must specify its target Context and one or more
 Responses per Context.  The TransactionReply is invoked by the
 responder when it has processed the TransactionRequest.

Groves, et al. Standards Track [Page 69] RFC 3525 Gateway Control Protocol June 2003

 A TransactionRequest has been processed:
  1. when all actions in that TransactionRequest have been processed;

or

  1. when an error is encountered in processing that

TransactionRequest, except when the error is in an optional

    command.
 A command has been processed when all descriptors in that command
 have been processed.
 A SignalsDescriptor is considered to have been processed when it has
 been established that the descriptor is syntactically valid, the
 requested signals are supported and they have been queued to be
 applied.
 An EventsDescriptor or EventBufferDescriptor is considered to have
 been processed when it has been established that the descriptor is
 syntactically valid, the requested events can be observed, any
 embedded signals can be generated, any embedded events can be
 detected, and the MG has been brought into a state in which the
 events will be detected.
   TransactionReply(TransactionID {
       ContextID { Response ... Response },
          . . .
       ContextID { Response ... Response } })
 The TransactionID parameter must be the same as that of the
 corresponding TransactionRequest.
 The ContextID parameter must specify a value to pertain to all
 Responses for the action.  The ContextID may be specific, all or
 null.
 Each of the Response parameters represents a return value as
 mentioned in 7.2, or an error descriptor if the command execution
 encountered an error.  Commands after the point of failure are not
 processed and, therefore, Responses are not issued for them.
 An exception to this occurs if a command has been marked as optional
 in the Transaction request.  If the optional command generates an
 error, the transaction still continues to execute, so the Reply
 would, in this case, have Responses after an Error.
 Section 7.1.19 Error Descriptor specifies the generation of error
 descriptors.  The text below discusses several individual cases.

Groves, et al. Standards Track [Page 70] RFC 3525 Gateway Control Protocol June 2003

 If the receiver encounters an error in processing a ContextID, the
 requested Action response will consist of the Context ID and a single
 error descriptor, 422 - Syntax Error in Action.
 If the receiver encounters an error such that it cannot determine a
 legal Action, it will return a TransactionReply consisting of the
 TransactionID and a single error descriptor, 422 - Syntax Error in
 Action.  If the end of an action cannot be reliably determined but
 one or more commands can be parsed, it will process them and then
 send 422 - Syntax Error in Action as the last action for the
 transaction.  If the receiver encounters an error such that is cannot
 determine a legal Transaction, it will return a TransactionReply with
 a null TransactionID and a single error descriptor (403 - Syntax
 Error in TransactionRequest).
 If the end of a transaction cannot be reliably determined and one or
 more Actions can be parsed, it will process them and then return 403
 - Syntax Error in Transaction as the last action reply for the
 transaction.  If no Actions can be parsed, it will return 403 -
 Syntax Error in TransactionRequest as the only reply.
 If the terminationID cannot be reliably determined, it will send 442
 - Syntax Error in Command as the action reply.
 If the end of a command cannot be reliably determined, it will return
 442 - Syntax Error in Command as the reply to the last action it can
 parse.

8.2.3 TransactionPending

 The receiver invokes the TransactionPending.  A TransactionPending
 indicates that the Transaction is actively being processed, but has
 not been completed.  It is used to prevent the sender from assuming
 the TransactionRequest was lost where the Transaction will take some
 time to complete.
   TransactionPending(TransactionID { } )
 The TransactionID parameter must be the same as that of the
 corresponding TransactionRequest.  A property of root
 (normalMGExecutionTime) is settable by the MGC to indicate the
 interval within which the MGC expects a response to any transaction
 from the MG.  Another property (normalMGCExecutionTime) is settable
 by the MGC to indicate the interval within which the MG should expect
 a response to any transaction from the MGC.  Senders may receive more
 than one TransactionPending for a command.  If a duplicate request is

Groves, et al. Standards Track [Page 71] RFC 3525 Gateway Control Protocol June 2003

 received when pending, the responder may send a duplicate pending
 immediately, or continue waiting for its timer to trigger another
 TransactionPending.

8.3 Messages

 Multiple Transactions can be concatenated into a Message.  Messages
 have a header, which includes the identity of the sender.  The
 Message Identifier (MID) of a message is set to a provisioned name
 (e.g., domain address/domain name/device name) of the entity
 transmitting the message.  Domain name is a suggested default.  An
 H.248.1 entity (MG/MGC) must consistently use the same MID in all
 messages it originates for the duration of control association with
 the peer (MGC/MG).
 Every Message contains a Version Number identifying the version of
 the protocol the message conforms to.  Versions consist of one or two
 digits, beginning with version 1 for the present version of the
 protocol.
 The transactions in a message are treated independently.  There is no
 order implied; there is no application or protocol acknowledgement of
 a message.  A message is essentially a transport mechanism.  For
 example, message X containing transaction requests A, B, and C may be
 responded to with message Y containing replies to A and C and message
 Z containing the reply to B.  Likewise, message L containing request
 D and message M containing request E may be responded to with message
 N containing replies to both D and E.

9 Transport

 The transport mechanism for the protocol should allow the reliable
 transport of transactions between a MGC and MG.  The transport shall
 remain independent of what particular commands are being sent and
 shall be applicable to all application states.  There are several
 transports defined for the protocol, which are defined in Annexes to
 this RFC and other Recommendations of the H.248
 sub-series.  Additional Transports may be defined as additional
 Recommendations of the H.248 sub-series.  For transport of the
 protocol over IP, MGCs shall implement both TCP and UDP/ALF, a MG
 shall implement TCP or UDP/ALF or both.
 The MG is provisioned with a name or address (such as DNS name or IP
 address) of a primary and zero or more secondary MGCs (see 7.2.8)
 that is the address the MG uses to send messages to the MGC.  If TCP
 or UDP is used as the protocol transport and the port to which the
 initial ServiceChange request is to be sent is not otherwise known,

Groves, et al. Standards Track [Page 72] RFC 3525 Gateway Control Protocol June 2003

 that request should be sent to the default port number for the
 protocol.  This port number is 2944 for text-encoded operation or
 2945 for binary-encoded operation, for either UDP or TCP.  The MGC
 receives the message containing the ServiceChange request from the MG
 and can determine the MG's address from it.  As described in 7.2.8,
 either the MG or the MGC may supply an address in the
 ServiceChangeAddress parameter to which subsequent transaction
 requests must be addressed, but responses (including the response to
 the initial ServiceChange request) must always be sent back to the
 address which was the source of the corresponding request.  For
 example, in IP networks, this is the source address in the IP header
 and the source port number in the TCP/UDP/SCTP header.

9.1 Ordering of Commands

 This RFC does not mandate that the underlying transport protocol
 guarantees the sequencing of transactions sent to an entity.  This
 property tends to maximize the timeliness of actions, but it has a
 few drawbacks.  For example:
  1. Notify commands may be delayed and arrive at the MGC after the

transmission of a new command changing the EventsDescriptor.

  1. If a new command is transmitted before a previous one is

acknowledged, there is no guarantee that prior command will be

    executed before the new one.
 Media Gateway Controllers that want to guarantee consistent operation
 of the Media Gateway may use the following rules.  These rules are
 with respect to commands that are in different transactions.
 Commands that are in the same transaction are executed in order (see
 clause 8).
 1) When a Media Gateway handles several Terminations, commands
    pertaining to the different Terminations may be sent in parallel,
    for example following a model where each Termination (or group of
    Terminations) is controlled by its own process or its own thread.
 2) On a Termination, there should normally be at most one outstanding
    command (Add or Modify or Move), unless the outstanding commands
    are in the same transaction.  However, a Subtract command may be
    issued at any time.  In consequence, a Media Gateway may sometimes
    receive a Modify command that applies to a previously subtracted
    Termination.  Such commands should be ignored, and an error code
    should be returned.

Groves, et al. Standards Track [Page 73] RFC 3525 Gateway Control Protocol June 2003

 3) For transports that do not guarantee in-sequence delivery of
    messages (i.e., UDP), there should normally be on a given
    Termination at most one outstanding Notify command at any time.
 4) In some cases, an implicitly or explicitly wildcarded Subtract
    command that applies to a group of Terminations may step in front
    of a pending Add command.  The Media Gateway Controller should
    individually delete all Terminations for which an Add command was
    pending at the time of the global Subtract command.  Also, new Add
    commands for Terminations named by the wildcarding (or implied in
    a Multiplex descriptor) should not be sent until the wildcarded
    Subtract command is acknowledged.
 5) AuditValue and AuditCapability are not subject to any sequencing.
 6) ServiceChange shall always be the first command sent by a MG as
    defined by the restart procedure.  Any other command or response
    must be delivered after this ServiceChange command.
 These rules do not affect the command responder, which should always
 respond to commands.

9.2 Protection against Restart Avalanche

 In the event that a large number of Media Gateways are powered on
 simultaneously and they were to all initiate a ServiceChange
 transaction, the Media Gateway Controller would very likely be
 swamped, leading to message losses and network congestion during the
 critical period of service restoration.  In order to prevent such
 avalanches, the following behaviour is suggested:
 1) When a Media Gateway is powered on, it should initiate a restart
    timer to a random value, uniformly distributed between 0 and a
    maximum waiting delay (MWD).  Care should be taken to avoid
    synchronicity of the random number generation between multiple
    Media Gateways that would use the same algorithm.
 2) The Media Gateway should then wait for either the end of this
    timer or the detection of a local user activity, such as for
    example an off-hook transition on a residential Media Gateway.
 3) When the timer elapses, or when an activity is detected, the Media
    Gateway should initiate the restart procedure.
 The restart procedure simply requires the MG to guarantee that the
 first message that the Media Gateway Controller sees from this MG is
 a ServiceChange message informing the Media Gateway Controller about
 the restart.

Groves, et al. Standards Track [Page 74] RFC 3525 Gateway Control Protocol June 2003

   NOTE - The value of MWD is a configuration parameter that depends
   on the type of the Media Gateway.  The following reasoning may be
   used to determine the value of this delay on residential gateways.
 Media Gateway Controllers are typically dimensioned to handle the
 peak hour traffic load, during which, in average, 10% of the lines
 will be busy, placing calls whose average duration is typically 3
 minutes.  The processing of a call typically involves 5 to 6 Media
 Gateway Controller transactions between each Media Gateway and the
 Media Gateway Controller.  This simple calculation shows that the
 Media Gateway Controller is expected to handle 5 to 6 transactions
 for each Termination, every 30 minutes on average, or, to put it
 otherwise, about one transaction per Termination every 5 to 6 minutes
 on average.  This suggests that a reasonable value of MWD for a
 residential gateway would be 10 to 12 minutes.  In the absence of
 explicit configuration, residential gateways should adopt a value of
 600 seconds for MWD.
 The same reasoning suggests that the value of MWD should be much
 shorter for trunking gateways or for business gateways, because they
 handle a large number of Terminations, and also because the usage
 rate of these Terminations is much higher than 10% during the peak
 busy hour, a typical value being 60%.  These Terminations, during the
 peak hour, are this expected to contribute about one transaction per
 minute to the Media Gateway Controller load.  A reasonable algorithm
 is to make the value of MWD per "trunk" Termination six times shorter
 than the MWD per residential gateway, and also inversely proportional
 to the number of Terminations that are being restarted.  For example
 MWD should be set to 2.5 seconds for a gateway that handles a T1
 line, or to 60 milliseconds for a gateway that handles a T3 line.

10 Security Considerations

 This clause covers security when using the protocol in an IP
 environment.

10.1 Protection of Protocol Connections

 A security mechanism is clearly needed to prevent unauthorized
 entities from using the protocol defined in this RFC for setting up
 unauthorized calls or interfering with authorized calls.  The
 security mechanism for the protocol when transported over IP networks
 is IPsec [RFC 2401 to RFC 2411].
 The AH header [RFC 2402] affords data origin authentication,
 connectionless integrity and optional anti-replay protection of
 messages passed between the MG and the MGC.  The ESP header [RFC
 2406] provides confidentiality of messages, if desired.  For

Groves, et al. Standards Track [Page 75] RFC 3525 Gateway Control Protocol June 2003

 instance, the ESP encryption service should be requested if the
 session descriptions are used to carry session keys, as defined in
 SDP.
 Implementations of the protocol defined in this RFC employing the ESP
 header SHALL comply with section 5 of [RFC 2406], which defines a
 minimum set of algorithms for integrity checking and encryption.
 Similarly, implementations employing the AH header SHALL comply with
 section 5 of [RFC 2402], which defines a minimum set of algorithms
 for integrity checking using manual keys.
 Implementations SHOULD use IKE [RFC 2409] to permit more robust
 keying options.  Implementations employing IKE SHOULD support
 authentication with RSA signatures and RSA public key encryption.

10.2 Interim AH scheme

 Implementation of IPsec requires that the AH or ESP header be
 inserted immediately after the IP header.  This cannot be easily done
 at the application level.  Therefore, this presents a deployment
 problem for the protocol defined in this RFC where the underlying
 network implementation does not support IPsec.
 As an interim solution, an optional AH header is defined within the
 H.248.1 protocol header.  The header fields are exactly those of the
 SPI, SEQUENCE NUMBER and DATA fields as defined in [RFC 2402].  The
 semantics of the header fields are the same as the "transport mode"
 of [RFC 2402], except for the calculation of the Integrity Check
 Value (ICV).  In IPsec, the ICV is calculated over the entire IP
 packet including the IP header.  This prevents spoofing of the IP
 addresses.  To retain the same functionality, the ICV calculation
 should be performed across all the transactions (concatenated) in the
 message prepended by a synthesized IP header consisting of a 32-bit
 source IP address, a 32-bit destination address and a 16-bit UDP
 destination port encoded as 20 hex digits.  When the interim AH
 mechanism is employed when TCP is the transport Layer, the UDP Port
 above becomes the TCP port, and all other operations are the same.
 Implementations of the H.248.1 protocol SHALL implement IPsec where
 the underlying operating system and the transport network supports
 IPsec.  Implementations of the protocol using IPv4 SHALL implement
 the interim AH scheme.  However, this interim scheme SHALL NOT be
 used when the underlying network layer supports IPsec.  IPv6
 implementations are assumed to support IPsec and SHALL NOT use the
 interim AH scheme.

Groves, et al. Standards Track [Page 76] RFC 3525 Gateway Control Protocol June 2003

 All implementations of the interim AH mechanism SHALL comply with
 section 5 of RFC 2402 which defines a minimum set of algorithms for
 integrity checking using manual keys.
 The interim AH interim scheme does not provide protection against
 eavesdropping, thus forbidding third parties from monitoring the
 connections set up by a given Termination.  Also, it does not provide
 protection against replay attacks.  These procedures do not
 necessarily protect against denial of service attacks by misbehaving
 MGs or misbehaving MGCs.  However, they will provide an
 identification of these misbehaving entities, which should then be
 deprived of their authorization through maintenance procedures.

10.3 Protection of Media Connections

 The protocol allows the MGC to provide MGs with "session keys" that
 can be used to encrypt the audio messages, protecting against
 eavesdropping.
 A specific problem of packet networks is "uncontrolled barge-in".
 This attack can be performed by directing media packets to the IP
 address and UDP port used by a connection.  If no protection is
 implemented, the packets must be decompressed and the signals must be
 played on the "line side".
 A basic protection against this attack is to only accept packets from
 known sources, checking for example that the IP source address and
 UDP source port match the values announced in the Remote descriptor.
 This has two inconveniences: it slows down connection establishment
 and it can be fooled by source spoofing:
  1. To enable the address-based protection, the MGC must obtain the

remote session description of the egress MG and pass it to the

    ingress MG.  This requires at least one network round trip, and
    leaves us with a dilemma: either allow the call to proceed without
    waiting for the round trip to complete, and risk for example,
    "clipping" a remote announcement, or wait for the full round trip
    and settle for slower call-set up procedures.
  1. Source spoofing is only effective if the attacker can obtain valid

pairs of source destination addresses and ports, for example by

    listening to a fraction of the traffic.  To fight source spoofing,
    one could try to control all access points to the network.  But
    this is in practice very hard to achieve.

Groves, et al. Standards Track [Page 77] RFC 3525 Gateway Control Protocol June 2003

 An alternative to checking the source address is to encrypt and
 authenticate the packets, using a secret key that is conveyed during
 the call set-up procedure.  This will not slow down the call set-up,
 and provides strong protection against address spoofing.

11 MG-MGC Control Interface

 The control association between MG and MGC is initiated at MG cold
 start, and announced by a ServiceChange message, but can be changed
 by subsequent events, such as failures or manual service events.
 While the protocol does not have an explicit mechanism to support
 multiple MGCs controlling a physical MG, it has been designed to
 support the multiple logical MG (within a single physical MG) that
 can be associated with different MGCs.

11.1 Multiple Virtual MGs

 A physical Media Gateway may be partitioned into one or more Virtual
 MGs.  A virtual MG consists of a set of statically partitioned
 physical Terminations and/or sets of ephemeral Terminations.  A
 physical Termination is controlled by one MGC.  The model does not
 require that other resources be statically allocated, just
 Terminations.  The mechanism for allocating Terminations to virtual
 MGs is a management method outside the scope of the protocol.  Each
 of the virtual MGs appears to the MGC as a complete MG client.
 A physical MG may have only one network interface, which must be
 shared across virtual MGs.  In such a case, the packet/cell side
 Termination is shared.  It should be noted however, that in use, such
 interfaces require an ephemeral instance of the Termination to be
 created per flow, and thus sharing the Termination is
 straightforward.  This mechanism does lead to a complication, namely
 that the MG must always know which of its controlling MGCs should be
 notified if an event occurs on the interface.
 In normal operation, the Virtual MG will be instructed by the MGC to
 create network flows (if it is the originating side), or to expect
 flow requests (if it is the terminating side), and no confusion will
 arise.  However, if an unexpected event occurs, the Virtual MG must
 know what to do with respect to the physical resources it is
 controlling.
 If recovering from the event requires manipulation of a physical
 interface's state, only one MGC should do so.  These issues are
 resolved by allowing any of the MGCs to create EventsDescriptors to
 be notified of such events, but only one MGC can have read/write

Groves, et al. Standards Track [Page 78] RFC 3525 Gateway Control Protocol June 2003

 access to the physical interface properties; all other MGCs have
 read-only access.  The management mechanism is used to designate
 which MGC has read/write capability, and is designated the Master
 MGC.
 Each virtual MG has its own Root Termination.  In most cases the
 values for the properties of the Root Termination are independently
 settable by each MGC.  Where there can only be one value, the
 parameter is read-only to all but the Master MGC.
 ServiceChange may only be applied to a Termination or set of
 Terminations partitioned to the Virtual MG or created (in the case of
 ephemeral Terminations) by that Virtual MG.

11.2 Cold start

 A MG is pre-provisioned by a management mechanism outside the scope
 of this protocol with a primary and (optionally) an ordered list of
 secondary MGCs.  Upon a cold start of the MG, it will issue a
 ServiceChange command with a "Restart" method, on the Root
 Termination to its primary MGC.  If the MGC accepts the MG, it sends
 a Transaction Reply not including a ServiceChangeMgcId parameter.  If
 the MGC does not accept the MG's registration, it sends a Transaction
 Reply, providing the address of an alternate MGC to be contacted by
 including a ServiceChangeMgcId parameter.
 If the MG receives a Transaction Reply that includes a
 ServiceChangeMgcId parameter, it sends a ServiceChange to the MGC
 specified in the ServiceChangeMgcId.  It continues this process until
 it gets a controlling MGC to accept its registration, or it fails to
 get a reply.  Upon failure to obtain a reply, either from the primary
 MGC, or a designated successor, the MG tries its pre-provisioned
 secondary MGCs, in order.  If the MG is unable to establish a control
 relationship with any MGC, it shall wait a random amount of time as
 described in 9.2 and then start contacting its primary, and if
 necessary, its secondary MGCs again.
 It is possible that the reply to a ServiceChange with Restart will be
 lost, and a command will be received by the MG prior to the receipt
 of the ServiceChange response.  The MG shall issue Error 505 -
 Command Received before a ServiceChange Reply has been received.

11.3 Negotiation of protocol version

 The first ServiceChange command from a MG shall contain the version
 number of the protocol supported by the MG in the
 ServiceChangeVersion parameter.  Upon receiving such a message, if
 the MGC supports only a lower version, then the MGC shall send a

Groves, et al. Standards Track [Page 79] RFC 3525 Gateway Control Protocol June 2003

 ServiceChangeReply with the lower version and thereafter all the
 messages between MG and MGC shall conform to the lower version of the
 protocol.  If the MG is unable to comply and it has established a
 transport connection to the MGC, it should close that connection.  In
 any event, it should reject all subsequent requests from the MGC with
 error 406 - Version Not Supported.
 If the MGC supports a higher version than the MG but is able to
 support the lower version proposed by the MG, it shall send a
 ServiceChangeReply with the lower version and thereafter all the
 messages between MG and MGC shall conform to the lower version of the
 protocol.  If the MGC is unable to comply, it shall reject the
 association, with error 406 - Version Not Supported.
 Protocol version negotiation may also occur at "handoff" and
 "failover" ServiceChanges.
 When extending the protocol with new versions, the following rules
 should be followed:
 1) Existing protocol elements, i.e., procedures, parameters,
    descriptor, property, values, should not be changed unless a
    protocol error needs to be corrected or it becomes necessary to
    change the operation of the service that is being supported by the
    protocol.
 2) The semantics of a command, a parameter, a descriptor, a property,
    or a value should not be changed.
 3) Established rules for formatting and encoding messages and
    parameters should not be modified.
 4) When information elements are found to be obsolete they can be
    marked as not used.  However, the identifier for that information
    element will be marked as reserved.  In that way it can not be
    used in future versions.

11.4 Failure of a MG

 If a MG fails, but is capable of sending a message to the MGC, it
 sends a ServiceChange with an appropriate method (graceful or forced)
 and specifies the Root TerminationID.  When it returns to service, it
 sends a ServiceChange with a "Restart" method.
 Allowing the MGC to send duplicate messages to both MGs accommodates
 pairs of MGs that are capable of redundant failover of one of the
 MGs.  Only the Working MG shall accept or reject transactions.  Upon
 failover, the primary MG sends a ServiceChange command with a

Groves, et al. Standards Track [Page 80] RFC 3525 Gateway Control Protocol June 2003

 "Failover" method and a "MG Impending Failure" reason.  The MGC then
 uses the secondary MG as the active MG.  When the error condition is
 repaired, the Working MG can send a "ServiceChange" with a "Restart"
 method.
   Note: Redundant failover MGs require a reliable transport, because
   the protocol provides no means for a secondary MG running ALF to
   acknowledge messages sent from the MGC.

11.5 Failure of an MGC

 If the MG detects a failure of its controlling MGC, it attempts to
 contact the next MGC on its pre-provisioned list.  It starts its
 attempts at the beginning (primary MGC), unless that was the MGC that
 failed, in which case it starts at its first secondary MGC.  It sends
 a ServiceChange message with a "Failover" method and a "MGC Impending
 Failure" reason.  If the MG is unable to establish a control
 relationship with any MGC, it shall wait a random amount of time as
 described in section 9.2 and then start again contacting its primary,
 and (if necessary) its secondary MGCs.  When contacting its
 previously controlling MGC, the MG sends the ServiceChange message
 with "Disconnected" method.
 In partial failure, or for manual maintenance reasons, an MGC may
 wish to direct its controlled MGs to use a different MGC.  To do so,
 it sends a ServiceChange method to the MG with a "HandOff" method,
 and its designated replacement in ServiceChangeMgcId.  If "HandOff"
 is supported, the MG shall send a ServiceChange message with a
 "Handoff" method and a "MGC directed change" reason to the designated
 MGC.  If it fails to get a reply from the designated MGC, the MG
 shall behave as if its MGC failed, and start contacting secondary
 MGCs as specified in the previous paragraph.  If the MG is unable to
 establish a control relationship with any MGC, it shall wait a random
 amount of time as described in 9.2 and then start contacting its
 primary, and if necessary, its secondary MGCs again.
 No recommendation is made on how the MGCs involved in the Handoff
 maintain state information; this is considered to be out of scope of
 this RFC.  The MGC and MG may take the following steps when Handoff
 occurs.  When the MGC initiates a HandOff, the handover should be
 transparent to Operations on the Media Gateway.  Transactions can be
 executed in any order, and could be in progress when the
 ServiceChange is executed.  Accordingly, commands in progress
 continue and replies to all commands from the original MGC must be
 sent to the transport address from which they were sent.  If the
 service relationship with the sending MGC has ended, the replies
 should be discarded.  The MG may receive outstanding transaction
 replies from the new MGC.  No new messages shall be sent to the new

Groves, et al. Standards Track [Page 81] RFC 3525 Gateway Control Protocol June 2003

 MGC until the control association is established.  Repeated
 transaction requests shall be directed to the new MGC.  The MG shall
 maintain state on all Terminations and Contexts.
 It is possible that the MGC could be implemented in such a way that a
 failed MGC is replaced by a working MGC where the identity of the new
 MGC is the same as the failed one.  In such a case,
 ServiceChangeMgcId would be specified with the previous value and the
 MG shall behave as if the value was changed, and send a ServiceChange
 message, as above.
 Pairs of MGCs that are capable of redundant failover can notify the
 controlled MGs of the failover by the above mechanism.

12 Package definition

 The primary mechanism for extension is by means of Packages.
 Packages define additional Properties, Events, Signals and Statistics
 that may occur on Terminations.
 Packages defined by IETF will appear in separate RFCs.
 Packages defined by ITU-T may appear in the relevant Recommendations
 (e.g., as Recommendations of the H.248 sub-series).
 1) A public document or a standard forum document, which can be
    referenced as the document that describes the package following
    the guideline above, should be specified.
 2) The document shall specify the version of the Package that it
    describes.
 3) The document should be available on a public web server and should
    have a stable URL.  The site should provide a mechanism to provide
    comments and appropriate responses should be returned.

12.1 Guidelines for defining packages

 Packages define Properties, Events, Signals, and Statistics.
 Packages may also define new error codes according to the guidelines
 given in 13.2.  This is a matter of documentary convenience: the
 package documentation is submitted to IANA in support of the error
 code registration.  If a package is modified, it is unnecessary to
 provide IANA with a new document reference in support of the error
 code unless the description of the error code itself is modified.

Groves, et al. Standards Track [Page 82] RFC 3525 Gateway Control Protocol June 2003

 Names of all such defined constructs shall consist of the PackageID
 (which uniquely identifies the package) and the ID of the item (which
 uniquely identifies the item in that package).  In the text encoding
 the two shall be separated by a forward slash ("/") character.
 Example: togen/playtone is the text encoding to refer to the play
 tone signal in the tone generation package.
 A Package will contain the following sections:

12.1.1 Package

 Overall description of the package, specifying:
    Package Name: only descriptive
    PackageID: is an identifier
    Description:
    Version:
       A new version of a package can only add additional Properties,
       Events, Signals, Statistics and new possible values for an
       existing parameter described in the original package.  No
       deletions or modifications shall be allowed.  A version is an
       integer in the range from 1 to 99.
    Designed to be extended only (Optional):
       This indicates that the package has been expressly designed to
       be extended by others, not to be directly referenced.  For
       example, the package may not have any function on its own or be
       nonsensical on its own.  The MG SHOULD NOT publish this
       PackageID when reporting packages.
    Extends (Optional): existing package Descriptor
       A package may extend an existing package.  The version of the
       original package must be specified.  When a package extends
       another package it shall only add additional Properties,
       Events, Signals, Statistics and new possible values for an
       existing parameter described in the original package.  An
       extended package shall not redefine or overload an identifier
       defined in the original package and packages it may have
       extended (multiple levels of extension).  Hence, if package B
       version 1 extends package A version 1, version 2 of B will not
       be able to extend the A version 2 if A version 2 defines a name
       already in B version 1.

Groves, et al. Standards Track [Page 83] RFC 3525 Gateway Control Protocol June 2003

12.1.2 Properties

 Properties defined by the package, specifying:
    Property Name: only descriptive
    PropertyID: is an identifier
    Description:
    Type: One of:
       Boolean
       String: UTF-8 string
       Octet String: A number of octets.  See Annex A and Annex B.3
       for encoding
       Integer: 4 byte signed integer
       Double: 8 byte signed integer
       Character: unicode UTF-8 encoding of a single letter.  Could be
       more than one octet.
       Enumeration: one of a list of possible unique values (see 12.3)
       Sub-list: a list of several values from a list.  The type of
       sub-list SHALL also be specified.  The type shall be chosen
       from the types specified in this section (with the exception of
       sub-list).  For example, Type: sub-list of enumeration.  The
       encoding of sub-lists is specified in Annexes A and B.3.
    Possible values:
       A package MUST specify either a specific set of values or a
       description of how values are determined.  A package MUST also
       specify a default value or the default behaviour when the value
       is omitted from its descriptor.  For example, a package may
       specify that procedures related to the property are suspended
       when its value is omitted.  A default value (but not
 procedures)
       may be specified as provisionable.
    Defined in:
       Which H.248.1 descriptor the property is defined in.

Groves, et al. Standards Track [Page 84] RFC 3525 Gateway Control Protocol June 2003

       LocalControl is for stream dependent properties.
       TerminationState is for stream independent properties.  These
       are expected to be the most common cases, but it is possible
       for properties to be defined in other descriptors.
    Characteristics: Read/Write or both, and (optionally), global:
       Indicates whether a property is read-only, or read-write, and
       if it is global.  If Global is omitted, the property is not
       global.  If a property is declared as global, the value of the
       property is shared by all Terminations realizing the package.

12.1.3 Events

 Events defined by the package, specifying:
    Event name: only descriptive
    EventID: is an identifier
    Description:
    EventsDescriptor Parameters:
       Parameters used by the MGC to configure the event, and found in
       the EventsDescriptor.  See 12.2.
    ObservedEventsDescriptor Parameters:
       Parameters returned to the MGC in Notify requests and in
       replies to command requests from the MGC that audit
       ObservedEventsDescriptor, and found in the
       ObservedEventsDescriptor.  See 12.2.

12.1.4 Signals

 Signals defined by the package, specifying:
    Signal Name: only descriptive
    SignalID: is an identifier.  SignalID is used in a
    SignalsDescriptor
    Description
    SignalType: one of:
       OO (On/Off)

Groves, et al. Standards Track [Page 85] RFC 3525 Gateway Control Protocol June 2003

       TO (TimeOut)
       BR (Brief)
    NOTE - SignalType may be defined such that it is dependent on the
    value of one or more parameters.  The package MUST specify a
    default signal type.  If the default type is TO, the package MUST
    specify a default duration which may be provisioned.  A default
    duration is meaningless for BR.
    Duration: in hundredths of seconds
    Additional Parameters: see 12.2

12.1.5 Statistics

 Statistics defined by the package, specifying:
    Statistic name: only descriptive
    StatisticID: is an identifier
    StatisticID is used in a StatisticsDescriptor
    Description:
    Units: unit of measure, e.g., milliseconds, packets

12.1.6 Procedures

 Additional guidance on the use of the package.

12.2 Guidelines to defining Parameters to Events and Signals

 Parameter Name: only descriptive
 ParameterID: is an identifier.  The textual ParameterID of parameters
 to Events and Signals shall not start with "EPA" and "SPA",
 respectively.  The textual ParameterID shall also not be "ST",
 "Stream", "SY", "SignalType", "DR", "Duration", "NC",
 "NotifyCompletion", "KA", "Keepactive", "EB", "Embed", "DM" or
 "DigitMap".
 Type: One of:
    Boolean
    String: UTF-8 octet string

Groves, et al. Standards Track [Page 86] RFC 3525 Gateway Control Protocol June 2003

    Octet String: A number of octets.  See Annex A and Annex B.3 for
    encoding
    Integer: 4-octet signed integer
    Double: 8-octet signed integer
    Character: unicode UTF-8 encoding of a single letter.  Could be
    more than one octet.
    Enumeration: one of a list of possible unique values (see 12.3)
    Sub-list: a list of several values from a list (not supported for
    statistics).  The type of sub-list SHALL also be specified.  The
    type shall be chosen from the types specified in this section
    (with the exception of sub-list).  For example, Type: sub-list of
    enumeration.  The encoding of sub-lists is specified in Annexes A
    and B.3.
 Possible values:
    A package MUST specify either a specific set of values or a
    description of how values are determined.  A package MUST also
    specify a default value or the default behavior when the value is
    omitted from its descriptor.  For example, a package may specify
    that procedures related to the parameter are suspended when it
    value is omitted.  A default value (but not procedures) may be
    specified as provisionable.
 Description:

12.3 Lists

 Possible values for parameters include enumerations.  Enumerations
 may be defined in a list.  It is recommended that the list be IANA
 registered so that packages that extend the list can be defined
 without concern for conflicting names.

12.4 Identifiers

 Identifiers in text encoding shall be strings of up to 64 characters,
 containing no spaces, starting with an alphabetic character and
 consisting of alphanumeric characters and/or digits, and possibly
 including the special character underscore ("_").

Groves, et al. Standards Track [Page 87] RFC 3525 Gateway Control Protocol June 2003

 Identifiers in binary encoding are 2 octets long.
 Both text and binary values shall be specified for each identifier,
 including identifiers used as values in enumerated types.

12.5 Package registration

 A package can be registered with IANA for interoperability reasons.
 See clause 13 for IANA Considerations.

13 IANA Considerations

13.1 Packages

 The following considerations SHALL be met to register a package with
 IANA:
 1) A unique string name, unique serial number and version number is
    registered for each package.  The string name is used with text
    encoding.  The serial number shall be used with binary encoding.
    Serial Numbers 0x8000 to 0xFFFF are reserved for private use.
    Serial number 0 is reserved.
 2) A contact name, email and postal addresses for that contact shall
    be specified.  The contact information shall be updated by the
    defining organization as necessary.
 3) A reference to a document that describes the package, which should
    be public:
    The document shall specify the version of the Package that it
    describes.
    If the document is public, it should be located on a public web
    server and should have a stable URL.  The site should provide a
    mechanism to provide comments and appropriate responses should be
    returned.
 4) Packages registered by other than recognized standards bodies
    shall have a minimum package name length of 8 characters.
 5) All other package names are first come-first served if all other
    conditions are met.

Groves, et al. Standards Track [Page 88] RFC 3525 Gateway Control Protocol June 2003

13.2 Error codes

 The following considerations SHALL be met to register an error code
 with IANA:
 1) An error number and a one-line (80-character maximum) string is
    registered for each error.
 2) A complete description of the conditions under which the error is
    detected shall be included in a publicly available document.  The
    description shall be sufficiently clear to differentiate the error
    from all other existing error codes.
 3) The document should be available on a public web server and should
    have a stable URL.
 4) Error numbers registered by recognized standards bodies shall have
    3- or 4-character error numbers.
 5) Error numbers registered by all other organizations or individuals
    shall have 4-character error numbers.
 6) An error number shall not be redefined nor modified except by the
    organization or individual that originally defined it, or their
    successors or assigns.

13.3 ServiceChange reasons

 The following considerations SHALL be met to register service change
 reason with IANA:
 1) A one-phrase, 80-character maximum, unique reason code is
    registered for each reason.
 2) A complete description of the conditions under which the reason is
    used is detected shall be included in a publicly available
    document.  The description shall be sufficiently clear to
    differentiate the reason from all other existing reasons.
 3) The document should be available on a public web server and should
    have a stable URL.

Groves, et al. Standards Track [Page 89] RFC 3525 Gateway Control Protocol June 2003

ANNEX A - Binary encoding of the protocol

 This annex specifies the syntax of messages using the notation
 defined in Recommendation X.680; Information technology - Abstract
 Syntax Notation One (ASN.1): Specification of basic notation.
 Messages shall be encoded for transmission by applying the basic
 encoding rules specified in Recommendation X.690, Information
 Technology - ASN.1 Encoding Rules: Specification of Basic Encoding
 Rules (BER), Canonical Encoding Rules (CER) and Distinguished
 Encoding Rules.

A.1 Coding of wildcards

 The use of wildcards ALL and CHOOSE is allowed in the protocol.  This
 allows a MGC to partially specify Termination IDs and to let the MG
 choose from the values that conform to the partial specification.
 Termination IDs may encode a hierarchy of names.  This hierarchy is
 provisioned.  For instance, a TerminationID may consist of a trunk
 group, a trunk within the group and a circuit.  Wildcarding must be
 possible at all levels.  The following paragraphs explain how this is
 achieved.
 The ASN.1 description uses octet strings of up to 8 octets in length
 for Termination IDs.  This means that Termination IDs consist of at
 most 64 bits.  A fully specified Termination ID may be preceded by a
 sequence of wildcarding fields.  A wildcarding field is one octet in
 length.  Bit 7 (the most significant bit) of this octet specifies
 what type of wildcarding is invoked: if the bit value equals 1, then
 the ALL wildcard is used; if the bit value if 0, then the CHOOSE
 wildcard is used.  Bit 6 of the wildcarding field specifies whether
 the wildcarding pertains to one level in the hierarchical naming
 scheme (bit value 0) or to the level of the hierarchy specified in
 the wildcarding field plus all lower levels (bit value 1).  Bits 0
 through 5 of the wildcarding field specify the bit position in the
 Termination ID at which the wildcarding starts.
 We illustrate this scheme with some examples.  In these examples, the
 most significant bit in a string of bits appears on the left hand
 side.
 Assume that Termination IDs are three octets long and that each octet
 represents a level in a hierarchical naming scheme.  A valid
 Termination ID is:
    00000001 00011110 01010101.

Groves, et al. Standards Track [Page 90] RFC 3525 Gateway Control Protocol June 2003

 Addressing ALL names with prefix 00000001 00011110 is done as
 follows:
    wildcarding field: 10000111
    Termination ID: 00000001 00011110 xxxxxxxx.
 The values of the bits labeled "x" is irrelevant and shall be ignored
 by the receiver.
 Indicating to the receiver that it must choose a name with 00011110
 as the second octet is done as follows:
    wildcarding fields: 00010111 followed by 00000111
    Termination ID: xxxxxxxx 00011110 xxxxxxxx.
 The first wildcard field indicates a CHOOSE wildcard for the level in
 the naming hierarchy starting at bit 23, the highest level in our
 assumed naming scheme.  The second wildcard field indicates a CHOOSE
 wildcard for the level in the naming hierarchy starting at bit 7, the
 lowest level in our assumed naming scheme.
 Finally, a CHOOSE-wildcarded name with the highest level of the name
 equal to 00000001 is specified as follows:
    wildcard field: 01001111
    Termination ID: 0000001 xxxxxxxx xxxxxxxx .
 Bit value 1 at bit position 6 of the first octet of the wildcard
 field indicates that the wildcarding pertains to the specified level
 in the naming hierarchy and all lower levels.
 Context IDs may also be wildcarded.  In the case of Context IDs,
 however, specifying partial names is not allowed.  Context ID 0x0
 SHALL be used to indicate the NULL Context, Context ID 0xFFFFFFFE
 SHALL be used to indicate a CHOOSE wildcard, and Context ID
 0xFFFFFFFF SHALL be used to indicate an ALL wildcard.
 TerminationID 0xFFFFFFFFFFFFFFFF SHALL be used to indicate the ROOT
 Termination.

Groves, et al. Standards Track [Page 91] RFC 3525 Gateway Control Protocol June 2003

A.2 ASN.1 syntax specification

 This subclause contains the ASN.1 specification of the H.248.1
 protocol syntax.
   NOTE 1 - In case a transport mechanism is used that employs
   application level framing, the definition of Transaction below
   changes.  Refer to the annex or to the Recommendation of the H.248
   sub-series defining the transport mechanism for the definition that
   applies in that case.
   NOTE 2 - The ASN.1 specification below contains a clause defining
   TerminationIDList as a sequence of TerminationIDs.  The length of
   this sequence SHALL be one, except possibly when used in
   contextAuditResult.
   NOTE 3 - This syntax specification does not enforce all
   restrictions on element inclusions and values.  Some additional
   restrictions are stated in comments and other restrictions appear
   in the text of this RFC.  These additional restrictions
   are part of the protocol even though not enforced by this
   specification.
   NOTE 4 - The ASN.1 module in this Annex uses octet string types to
   encode values for property parameter, signal parameter and event
   parameter values and statistics.  The actual types of these values
   vary and are specified in Annex C or the relevant package
   definition.
 A value is first BER-encoded based on its type using the table below.
 The result of this BER-encoding is then encoded as an ASN.1 octet
 string, "double wrapping" the value.  The format specified in Annex C
 or the package relates to BER encoding according to the following
 table:
 Type Specified in Package   ASN.1 BER Type
 String                      IA5String or UTF8String (Note 4)
 Integer (4 Octet)           INTEGER
 Double (8 octet signed int) INTEGER (Note 3)
 Character (UTF-8, Note 1)   IA5String
 Enumeration                 ENUMERATED
 Boolean                     BOOLEAN

Groves, et al. Standards Track [Page 92] RFC 3525 Gateway Control Protocol June 2003

 Unsigned Integer (Note 2)   INTEGER  (Note 3)
 Octet (String)              OCTET STRING
   Note 1: Can be more than one byte
   Note 2: Unsigned integer is referenced in Annex C
   Note 3: The BER encoding of INTEGER does not imply the use of 4
   bytes.
   Note 4: String should be encoded as IA5String when the contents
   are all ASCII characters, but as UTF8String if it contains any
   Non-ASCII characters.
 See ITU-T Rec.  X.690, 8.7, for the definition of the encoding of an
 octet string value.
 MEDIA-GATEWAY-CONTROL DEFINITIONS AUTOMATIC TAGS::=
 BEGIN
 MegacoMessage ::= SEQUENCE
 {
    authHeader     AuthenticationHeader OPTIONAL,
    mess           Message
 }
 AuthenticationHeader ::= SEQUENCE
 {
    secParmIndex   SecurityParmIndex,
    seqNum         SequenceNum,
    ad             AuthData
 }
 SecurityParmIndex ::= OCTET STRING(SIZE(4))
 SequenceNum       ::= OCTET STRING(SIZE(4))
 AuthData          ::= OCTET STRING (SIZE (12..32))
 Message ::= SEQUENCE
 {
    version           INTEGER(0..99),
    -- The version of the protocol defined here is equal to 1.
    mId               MId,  -- Name/address of message originator
    messageBody       CHOICE
    {
       messageError      ErrorDescriptor,

Groves, et al. Standards Track [Page 93] RFC 3525 Gateway Control Protocol June 2003

       transactions      SEQUENCE OF Transaction
    },
    ...
 }
 MId ::= CHOICE
 {
    ip4Address           IP4Address,
    ip6Address           IP6Address,
    domainName           DomainName,
    deviceName           PathName,
    mtpAddress           OCTET STRING(SIZE(2..4)),
    -- Addressing structure of mtpAddress:
    --     25 - 15           0
    --        |  PC        | NI |
    --      24 - 14 bits    2 bits
    -- Note: 14 bits are defined for international use.
    -- Two national options exist where the point code is 16 or 24
    -- bits.
    -- To octet align the mtpAddress, the MSBs shall be encoded as 0s.
           ...
 }
 DomainName ::= SEQUENCE
 {
    name        IA5String,
    -- The name starts with an alphanumeric digit followed by a
    -- sequence of alphanumeric digits, hyphens and dots.  No two
    -- dots shall occur consecutively.
    portNumber     INTEGER(0..65535) OPTIONAL
 }
 IP4Address ::= SEQUENCE
 {
    address        OCTET STRING (SIZE(4)),
    portNumber     INTEGER(0..65535) OPTIONAL
 }
 IP6Address ::= SEQUENCE
 {
    address        OCTET STRING (SIZE(16)),
    portNumber     INTEGER(0..65535) OPTIONAL
 }
 PathName ::= IA5String(SIZE (1..64))
 -- See A.3
 Transaction ::= CHOICE

Groves, et al. Standards Track [Page 94] RFC 3525 Gateway Control Protocol June 2003

 {
    transactionRequest   TransactionRequest,
    transactionPending   TransactionPending,
    transactionReply     TransactionReply,
    transactionResponseAck  TransactionResponseAck,
        -- use of response acks is dependent on underlying transport
    ...
 }
 TransactionId ::= INTEGER(0..4294967295)  -- 32-bit unsigned integer
 TransactionRequest ::= SEQUENCE
 {
    transactionId        TransactionId,
    actions              SEQUENCE OF ActionRequest,
    ...
 }
 TransactionPending ::= SEQUENCE
 {
    transactionId        TransactionId,
    ...
 }
 TransactionReply ::= SEQUENCE
 {
    transactionId        TransactionId,
    immAckRequired       NULL OPTIONAL,
    transactionResult    CHOICE
    {
         transactionError   ErrorDescriptor,
         actionReplies      SEQUENCE OF ActionReply
    },
    ...
 }
 TransactionResponseAck ::= SEQUENCE OF TransactionAck
 TransactionAck ::= SEQUENCE
 {
    firstAck       TransactionId,
    lastAck        TransactionId OPTIONAL
 }
 ErrorDescriptor ::= SEQUENCE
 {
    errorCode      ErrorCode,
    errorText      ErrorText OPTIONAL
 }

Groves, et al. Standards Track [Page 95] RFC 3525 Gateway Control Protocol June 2003

 ErrorCode ::= INTEGER(0..65535)
 -- See clause 13 for IANA Considerations with respect to error codes
 ErrorText ::= IA5String
 ContextID ::= INTEGER(0..4294967295)
  1. - Context NULL Value: 0
  2. - Context CHOOSE Value: 4294967294 (0xFFFFFFFE)
  3. - Context ALL Value: 4294967295 (0xFFFFFFFF)
 ActionRequest ::= SEQUENCE
 {
    contextId         ContextID,
    contextRequest       ContextRequest OPTIONAL,
    contextAttrAuditReq  ContextAttrAuditRequest OPTIONAL,
    commandRequests   SEQUENCE OF CommandRequest
 }
 ActionReply ::= SEQUENCE
 {
    contextId         ContextID,
    errorDescriptor   ErrorDescriptor OPTIONAL,
    contextReply      ContextRequest OPTIONAL,
    commandReply      SEQUENCE OF CommandReply
 }
 ContextRequest ::= SEQUENCE
 {
    priority       INTEGER(0..15) OPTIONAL,
    emergency      BOOLEAN OPTIONAL,
    topologyReq    SEQUENCE OF TopologyRequest OPTIONAL,
    ...
 }
 ContextAttrAuditRequest ::= SEQUENCE
 {
    topology    NULL OPTIONAL,
    emergency   NULL OPTIONAL,
    priority    NULL OPTIONAL,
    ...
 }
 CommandRequest ::= SEQUENCE
 {
    command           Command,

Groves, et al. Standards Track [Page 96] RFC 3525 Gateway Control Protocol June 2003

    optional          NULL OPTIONAL,
    wildcardReturn    NULL OPTIONAL,
    ...
 }
 Command ::= CHOICE
 {
    addReq               AmmRequest,
    moveReq              AmmRequest,
    modReq               AmmRequest,
    -- Add, Move, Modify requests have the same parameters
    subtractReq          SubtractRequest,
    auditCapRequest      AuditRequest,
    auditValueRequest    AuditRequest,
    notifyReq            NotifyRequest,
    serviceChangeReq     ServiceChangeRequest,
    ...
 }
 CommandReply ::= CHOICE
 {
    addReply                AmmsReply,
    moveReply               AmmsReply,
    modReply                AmmsReply,
    subtractReply           AmmsReply,
    -- Add, Move, Modify, Subtract replies have the same parameters
    auditCapReply           AuditReply,
    auditValueReply         AuditReply,
    notifyReply             NotifyReply,
    serviceChangeReply      ServiceChangeReply,
    ...
 }
 TopologyRequest ::= SEQUENCE
 {
    terminationFrom         TerminationID,
    terminationTo           TerminationID,
    topologyDirection       ENUMERATED
    {
       bothway(0),
       isolate(1),
       oneway(2)
    },
    ...
 }
 AmmRequest ::= SEQUENCE
 {

Groves, et al. Standards Track [Page 97] RFC 3525 Gateway Control Protocol June 2003

    terminationID        TerminationIDList,
    descriptors          SEQUENCE OF AmmDescriptor,
    -- At most one descriptor of each type (see AmmDescriptor)
    -- allowed in the sequence.
    ...
 }
 AmmDescriptor ::= CHOICE
 {
    mediaDescriptor         MediaDescriptor,
    modemDescriptor         ModemDescriptor,
    muxDescriptor           MuxDescriptor,
    eventsDescriptor        EventsDescriptor,
    eventBufferDescriptor   EventBufferDescriptor,
    signalsDescriptor       SignalsDescriptor,
    digitMapDescriptor      DigitMapDescriptor,
    auditDescriptor         AuditDescriptor,
    ...
 }
 AmmsReply ::= SEQUENCE
 {
    terminationID        TerminationIDList,
    terminationAudit     TerminationAudit OPTIONAL,
    ...
 }
 SubtractRequest ::= SEQUENCE
 {
    terminationID        TerminationIDList,
    auditDescriptor      AuditDescriptor OPTIONAL,
    ...
 }
 AuditRequest ::= SEQUENCE
 {
    terminationID        TerminationID,
    auditDescriptor      AuditDescriptor,
    ...
 }
 AuditReply ::= CHOICE
 {
    contextAuditResult   TerminationIDList,
    error                ErrorDescriptor,
    auditResult          AuditResult,
    ...
 }

Groves, et al. Standards Track [Page 98] RFC 3525 Gateway Control Protocol June 2003

 AuditResult ::= SEQUENCE
 {
    terminationID           TerminationID,
    terminationAuditResult  TerminationAudit
 }
 TerminationAudit ::= SEQUENCE OF AuditReturnParameter
 AuditReturnParameter ::= CHOICE
 {
    errorDescriptor         ErrorDescriptor,
    mediaDescriptor         MediaDescriptor,
    modemDescriptor         ModemDescriptor,
    muxDescriptor           MuxDescriptor,
    eventsDescriptor        EventsDescriptor,
    eventBufferDescriptor   EventBufferDescriptor,
    signalsDescriptor       SignalsDescriptor,
    digitMapDescriptor      DigitMapDescriptor,
    observedEventsDescriptor   ObservedEventsDescriptor,
    statisticsDescriptor    StatisticsDescriptor,
    packagesDescriptor      PackagesDescriptor,
    emptyDescriptors        AuditDescriptor,
    ...
 }
 AuditDescriptor ::= SEQUENCE
 {
    auditToken  BIT STRING
       {
          muxToken(0), modemToken(1), mediaToken(2),
          eventsToken(3), signalsToken(4),
          digitMapToken(5), statsToken(6),
          observedEventsToken(7),
          packagesToken(8), eventBufferToken(9)
       } OPTIONAL,
    ...
 }
 NotifyRequest ::= SEQUENCE
 {
    terminationID              TerminationIDList,
    observedEventsDescriptor   ObservedEventsDescriptor,
    errorDescriptor            ErrorDescriptor OPTIONAL,
    ...
 }

Groves, et al. Standards Track [Page 99] RFC 3525 Gateway Control Protocol June 2003

 NotifyReply ::= SEQUENCE
 {
    terminationID           TerminationIDList,
    errorDescriptor         ErrorDescriptor OPTIONAL,
    ...
 }
 ObservedEventsDescriptor ::= SEQUENCE
 {
    requestId               RequestID,
    observedEventLst        SEQUENCE OF ObservedEvent
 }
 ObservedEvent ::= SEQUENCE
 {
    eventName            EventName,
    streamID             StreamID OPTIONAL,
    eventParList         SEQUENCE OF EventParameter,
    timeNotation         TimeNotation OPTIONAL,
    ...
 }
 EventName ::= PkgdName
 EventParameter ::= SEQUENCE
 {
    eventParameterName      Name,
    value                   Value,
 -- For use of extraInfo see the comment related to PropertyParm
    extraInfo CHOICE
    {
       relation Relation,
       range    BOOLEAN,
       sublist  BOOLEAN
    } OPTIONAL,
    ...
 }
 ServiceChangeRequest ::= SEQUENCE
 {
    terminationID           TerminationIDList,
    serviceChangeParms      ServiceChangeParm,
    ...
 }
 ServiceChangeReply ::= SEQUENCE
 {
    terminationID           TerminationIDList,

Groves, et al. Standards Track [Page 100] RFC 3525 Gateway Control Protocol June 2003

    serviceChangeResult     ServiceChangeResult,
    ...
 }
  1. - For ServiceChangeResult, no parameters are mandatory. Hence the
  2. - distinction between ServiceChangeParm and ServiceChangeResParm.
 ServiceChangeResult ::= CHOICE
 {
    errorDescriptor            ErrorDescriptor,
    serviceChangeResParms      ServiceChangeResParm
 }
 WildcardField ::= OCTET STRING(SIZE(1))
 TerminationID ::= SEQUENCE
 {
    wildcard SEQUENCE OF WildcardField,
    id    OCTET STRING(SIZE(1..8)),
    ...
 }
 -- See A.1 for explanation of wildcarding mechanism.
 -- Termination ID 0xFFFFFFFFFFFFFFFF indicates the ROOT Termination.
 TerminationIDList ::= SEQUENCE OF TerminationID
 MediaDescriptor ::= SEQUENCE
 {
    termStateDescr TerminationStateDescriptor OPTIONAL,
    streams     CHOICE
    {
       oneStream      StreamParms,
       multiStream    SEQUENCE OF StreamDescriptor
    } OPTIONAL,
    ...
 }
 StreamDescriptor ::= SEQUENCE
 {
    streamID          StreamID,
    streamParms       StreamParms
 }
 StreamParms ::= SEQUENCE
 {
    localControlDescriptor     LocalControlDescriptor OPTIONAL,
    localDescriptor            LocalRemoteDescriptor OPTIONAL,

Groves, et al. Standards Track [Page 101] RFC 3525 Gateway Control Protocol June 2003

    remoteDescriptor           LocalRemoteDescriptor OPTIONAL,
    ...
 }
 LocalControlDescriptor ::= SEQUENCE
 {
    streamMode        StreamMode OPTIONAL,
    reserveValue      BOOLEAN OPTIONAL,
    reserveGroup      BOOLEAN OPTIONAL,
    propertyParms     SEQUENCE OF PropertyParm,
    ...
 }
 StreamMode ::= ENUMERATED
 {
    sendOnly(0),
    recvOnly(1),
    sendRecv(2),
    inactive(3),
    loopBack(4),
       ...
 }
  1. - In PropertyParm, value is a SEQUENCE OF octet string. When sent
  2. - by an MGC the interpretation is as follows:
  3. - empty sequence means CHOOSE
  4. - one element sequence specifies value
  5. - If the sublist field is not selected, a longer sequence means
  6. - "choose one of the values" (i.e., value1 OR value2 OR …)
  7. - If the sublist field is selected,
  8. - a sequence with more than one element encodes the value of a
  9. - list-valued property (i.e., value1 AND value2 AND …).
  10. - The relation field may only be selected if the value sequence
  11. - has length 1. It indicates that the MG has to choose a value
  12. - for the property. E.g., x > 3 (using the greaterThan
  13. - value for relation) instructs the MG to choose any value larger
  14. - than 3 for property x.
  15. - The range field may only be selected if the value sequence
  16. - has length 2. It indicates that the MG has to choose a value
  17. - in the range between the first octet in the value sequence and
  18. - the trailing octet in the value sequence, including the
  19. - boundary values.
  20. - When sent by the MG, only responses to an AuditCapability request
  21. - may contain multiple values, a range, or a relation field.
 PropertyParm ::= SEQUENCE
 {

Groves, et al. Standards Track [Page 102] RFC 3525 Gateway Control Protocol June 2003

    name        PkgdName,
    value       SEQUENCE OF OCTET STRING,
    extraInfo   CHOICE
    {
       relation    Relation,
       range       BOOLEAN,
       sublist     BOOLEAN
    } OPTIONAL,
    ...
 }
 Name ::= OCTET STRING(SIZE(2))
 PkgdName ::= OCTET STRING(SIZE(4))
 -- represents Package Name (2 octets) plus Property, Event,
 -- Signal Names or Statistics ID. (2 octets)
 -- To wildcard a package use 0xFFFF for first two octets, choose
 -- is not allowed.  To reference native property tag specified in
 -- Annex C, use 0x0000 as first two octets.
 -- To wildcard a Property, Event, Signal, or Statistics ID, use
 -- 0xFFFF for last two octets, choose is not allowed.
 -- Wildcarding of Package Name is permitted only if Property,
 -- Event, Signal, or Statistics ID are
 -- also wildcarded.
 Relation ::= ENUMERATED
 {
    greaterThan(0),
    smallerThan(1),
    unequalTo(2),
    ...
 }
 LocalRemoteDescriptor ::= SEQUENCE
 {
    propGrps SEQUENCE OF PropertyGroup,
    ...
 }
 PropertyGroup ::= SEQUENCE OF PropertyParm
 TerminationStateDescriptor ::= SEQUENCE
 {
    propertyParms        SEQUENCE OF PropertyParm,
    eventBufferControl   EventBufferControl OPTIONAL,
    serviceState         ServiceState OPTIONAL,
    ...
 }

Groves, et al. Standards Track [Page 103] RFC 3525 Gateway Control Protocol June 2003

 EventBufferControl ::= ENUMERATED
 {
    off(0),
    lockStep(1),
    ...
 }
 ServiceState ::= ENUMERATED
 {
    test(0),
    outOfSvc(1),
    inSvc(2),
       ...
 }
 MuxDescriptor   ::= SEQUENCE
 {
    muxType           MuxType,
    termList          SEQUENCE OF TerminationID,
    nonStandardData   NonStandardData OPTIONAL,
    ...
 }
 MuxType ::= ENUMERATED
 {
    h221(0),
    h223(1),
    h226(2),
    v76(3),
    ...
 }
 StreamID ::= INTEGER(0..65535)   -- 16-bit unsigned integer
 EventsDescriptor ::= SEQUENCE
 {
    requestID      RequestID OPTIONAL,
                -- RequestID must be present if eventList
                -- is non empty
    eventList      SEQUENCE OF RequestedEvent,
    ...
 }
 RequestedEvent ::= SEQUENCE
 {
    pkgdName       PkgdName,

Groves, et al. Standards Track [Page 104] RFC 3525 Gateway Control Protocol June 2003

    streamID       StreamID OPTIONAL,
    eventAction    RequestedActions OPTIONAL,
    evParList      SEQUENCE OF EventParameter,
    ...
 }
 RequestedActions ::= SEQUENCE
 {
    keepActive        BOOLEAN OPTIONAL,
    eventDM           EventDM OPTIONAL,
    secondEvent          SecondEventsDescriptor OPTIONAL,
    signalsDescriptor    SignalsDescriptor OPTIONAL,
    ...
 }
 EventDM ::= CHOICE
 {  digitMapName   DigitMapName,
    digitMapValue  DigitMapValue
 }
 SecondEventsDescriptor ::= SEQUENCE
 {
    requestID         RequestID OPTIONAL,
    eventList         SEQUENCE OF SecondRequestedEvent,
    ...
 }
 SecondRequestedEvent ::= SEQUENCE
 {
    pkgdName          PkgdName,
    streamID          StreamID OPTIONAL,
    eventAction       SecondRequestedActions OPTIONAL,
    evParList         SEQUENCE OF EventParameter,
    ...
 }
 SecondRequestedActions ::= SEQUENCE
 {
    keepActive           BOOLEAN OPTIONAL,
    eventDM              EventDM OPTIONAL,
    signalsDescriptor    SignalsDescriptor OPTIONAL,
    ...
 }
 EventBufferDescriptor ::= SEQUENCE OF EventSpec
 EventSpec ::= SEQUENCE
 {

Groves, et al. Standards Track [Page 105] RFC 3525 Gateway Control Protocol June 2003

    eventName      EventName,
    streamID       StreamID OPTIONAL,
    eventParList   SEQUENCE OF EventParameter,
    ...
 }
 SignalsDescriptor ::= SEQUENCE OF SignalRequest
 SignalRequest ::=CHOICE
 {
    signal         Signal,
    seqSigList     SeqSigList,
    ...
 }
 SeqSigList ::= SEQUENCE
 {
    id                INTEGER(0..65535),
    signalList        SEQUENCE OF Signal
 }
 Signal ::= SEQUENCE
 {
    signalName        SignalName,
    streamID          StreamID OPTIONAL,
    sigType           SignalType OPTIONAL,
    duration          INTEGER (0..65535) OPTIONAL,
    notifyCompletion  NotifyCompletion OPTIONAL,
    keepActive        BOOLEAN OPTIONAL,
    sigParList        SEQUENCE OF SigParameter,
    ...
 }
 SignalType ::= ENUMERATED
 {
    brief(0),
    onOff(1),
    timeOut(2),
    ...
 }
 SignalName ::= PkgdName
 NotifyCompletion ::= BIT STRING
 {
    onTimeOut(0), onInterruptByEvent(1),
    onInterruptByNewSignalDescr(2), otherReason(3)
 }

Groves, et al. Standards Track [Page 106] RFC 3525 Gateway Control Protocol June 2003

 SigParameter ::= SEQUENCE
 {
    sigParameterName     Name,
    value                Value,
    -- For use of extraInfo see the comment related to PropertyParm
    extraInfo CHOICE
    {
       relation Relation,
       range    BOOLEAN,
       sublist  BOOLEAN
    } OPTIONAL,
    ...
 }
  1. - For an AuditCapReply with all events, the RequestID SHALL be ALL.
  2. - ALL is represented by 0xffffffff.
 RequestID ::= INTEGER(0..4294967295)   -- 32-bit unsigned integer
 ModemDescriptor ::= SEQUENCE
 {
    mtl               SEQUENCE OF ModemType,
    mpl               SEQUENCE OF PropertyParm,
    nonStandardData   NonStandardData OPTIONAL
 }
 ModemType ::= ENUMERATED
 {
    v18(0),
    v22(1),
    v22bis(2),
    v32(3),
    v32bis(4),
    v34(5),
    v90(6),
    v91(7),
    synchISDN(8),
    ...
 }
 DigitMapDescriptor ::= SEQUENCE
 {
    digitMapName   DigitMapName   OPTIONAL,
    digitMapValue  DigitMapValue  OPTIONAL
 }

Groves, et al. Standards Track [Page 107] RFC 3525 Gateway Control Protocol June 2003

 DigitMapName ::= Name
 DigitMapValue ::= SEQUENCE
 {
    startTimer     INTEGER(0..99) OPTIONAL,
    shortTimer     INTEGER(0..99) OPTIONAL,
    longTimer      INTEGER(0..99) OPTIONAL,
    digitMapBody      IA5String,
 -- Units are seconds for start, short and long timers, and
 -- hundreds of milliseconds for duration timer.  Thus start,
 -- short, and long range from 1 to 99 seconds and duration
 -- from 100 ms to 9.9 s
    -- See A.3 for explanation of digit map syntax
    ...
 }
 ServiceChangeParm ::= SEQUENCE
 {
    serviceChangeMethod     ServiceChangeMethod,
    serviceChangeAddress    ServiceChangeAddress OPTIONAL,
    serviceChangeVersion    INTEGER(0..99) OPTIONAL,
    serviceChangeProfile    ServiceChangeProfile OPTIONAL,
    serviceChangeReason     Value,
 -- A serviceChangeReason consists of a numeric reason code
 -- and an optional text description.
 -- The serviceChangeReason SHALL be a string consisting of
 -- a decimal reason code, optionally followed by a single
 -- space character and a textual description string.
 -- This string is first BER-encoded as an IA5String.
 -- The result of this BER-encoding is then encoded as
 -- an ASN.1 OCTET STRING type, "double wrapping" the
 -- value as was done for package elements.
    serviceChangeDelay      INTEGER(0..4294967295) OPTIONAL,
                                      -- 32-bit unsigned integer
    serviceChangeMgcId      MId OPTIONAL,
    timeStamp               TimeNotation OPTIONAL,
    nonStandardData         NonStandardData OPTIONAL,
    ...
 }
 ServiceChangeAddress ::= CHOICE
 {
    portNumber        INTEGER(0..65535),    -- TCP/UDP port number
    ip4Address        IP4Address,
    ip6Address        IP6Address,
    domainName        DomainName,
    deviceName        PathName,
    mtpAddress        OCTET STRING(SIZE(2..4)),

Groves, et al. Standards Track [Page 108] RFC 3525 Gateway Control Protocol June 2003

    ...
 }
 ServiceChangeResParm ::= SEQUENCE
 {
    serviceChangeMgcId      MId OPTIONAL,
    serviceChangeAddress    ServiceChangeAddress OPTIONAL,
    serviceChangeVersion    INTEGER(0..99) OPTIONAL,
    serviceChangeProfile    ServiceChangeProfile OPTIONAL,
    timestamp               TimeNotation OPTIONAL,
    ...
 }
 ServiceChangeMethod ::= ENUMERATED
 {
    failover(0),
    forced(1),
    graceful(2),
    restart(3),
    disconnected(4),
    handOff(5),
    ...
 }
 ServiceChangeProfile ::= SEQUENCE
 {
    profileName    IA5String(SIZE (1..67))
    -- 64 characters for name, 1 for "/", 2 for version to match ABNF
 }
 PackagesDescriptor ::= SEQUENCE OF PackagesItem
 PackagesItem ::= SEQUENCE
 {
    packageName       Name,
    packageVersion    INTEGER(0..99),
    ...
 }
 StatisticsDescriptor ::= SEQUENCE OF StatisticsParameter
 StatisticsParameter ::= SEQUENCE
 {
    statName       PkgdName,
    statValue      Value OPTIONAL
 }

Groves, et al. Standards Track [Page 109] RFC 3525 Gateway Control Protocol June 2003

 NonStandardData ::= SEQUENCE
 {
    nonStandardIdentifier   NonStandardIdentifier,
    data                    OCTET STRING
 }
 NonStandardIdentifier ::= CHOICE
 {
    object            OBJECT IDENTIFIER,
    h221NonStandard   H221NonStandard,
    experimental      IA5String(SIZE(8)),
        -- first two characters should be "X-" or "X+"
    ...
 }
 H221NonStandard ::= SEQUENCE
 {  t35CountryCode1   INTEGER(0..255),
    t35CountryCode2   INTEGER(0..255),      -- country, as per T.35
    t35Extension      INTEGER(0..255),      -- assigned nationally
    manufacturerCode     INTEGER(0..65535), -- assigned nationally
    ...
 }
 TimeNotation ::= SEQUENCE
 {
    date     IA5String(SIZE(8)),  -- yyyymmdd format
    time     IA5String(SIZE(8))   -- hhmmssss format
    -- per ISO 8601:1988
 }
 Value ::= SEQUENCE OF OCTET STRING
 END

Groves, et al. Standards Track [Page 110] RFC 3525 Gateway Control Protocol June 2003

A.3 Digit maps and path names

 From a syntactic viewpoint, digit maps are strings with syntactic
 restrictions imposed upon them.  The syntax of valid digit maps is
 specified in ABNF [RFC 2234].  The syntax for digit maps presented in
 this subclause is for illustrative purposes only.  The definition of
 digitMap in Annex B takes precedence in the case of differences
 between the two.
   digitMap = (digitString / LWSP "(" LWSP digitStringList LWSP ")"
             LWSP)
   digitStringList = digitString *( LWSP "|" LWSP digitString )
   digitString = 1*(digitStringElement)
   digitStringElement = digitPosition [DOT]
   digitPosition = digitMapLetter / digitMapRange
   digitMapRange = ("x" / (LWSP "[" LWSP digitLetter LWSP "]" LWSP))
   digitLetter = *((DIGIT "-" DIGIT) /digitMapLetter)
   digitMapLetter = DIGIT           ;digits 0-9
           / %x41-4B / %x61-6B    ;a-k and A-K
           / "L"/ "S"       ;Inter-event timers
                               ;(long, short)
           / "Z"            ;Long duration event
   DOT = %x2E ; "."
   LWSP = *(WSP / COMMENT / EOL)
   WSP = SP / HTAB
   COMMENT = ";" *(SafeChar / RestChar / WSP) EOL
   EOL = (CR [LF]) / LF
   SP = %x20
   HTAB = %x09
   CR = %x0D
   LF = %x0A
   SafeChar = DIGIT / ALPHA / "+" / "-" / "&" / "!" / "_" / "/" /
       "'" / "?" / "@" / "^" / "`" / "~" / "*" / "$" / "\" /
       "(" / ")" / "%" / "."
   RestChar = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#" /
       "<" / ">" / "=" / %x22
   DIGIT = %x30-39       ; digits 0 through 9
   ALPHA = %x41-5A / %x61-7A; A-Z, a-z
 A path name is also a string with syntactic restrictions imposed upon
 it.  The ABNF production defining it is copied from Annex B.
   ; Total length of pathNAME must not exceed 64 chars.
   pathNAME = ["*"] NAME *("/" / "*"/ ALPHA / DIGIT /"_" / "$" )
                          ["@" pathDomainName ]

Groves, et al. Standards Track [Page 111] RFC 3525 Gateway Control Protocol June 2003

   ; ABNF allows two or more consecutive "." although it is
   ; meaningless in a path domain name.
   pathDomainName       = (ALPHA / DIGIT / "*" )
                          *63(ALPHA / DIGIT / "-"
   NAME = ALPHA *63(ALPHA / DIGIT / "_" )

Groves, et al. Standards Track [Page 112] RFC 3525 Gateway Control Protocol June 2003

ANNEX B - Text encoding of the protocol

B.1 Coding of wildcards

 In a text encoding of the protocol, while TerminationIDs are
 arbitrary, by judicious choice of names, the wildcard character, "*"
 may be made more useful.  When the wildcard character is encountered,
 it will "match" all TerminationIDs having the same previous and
 following characters (if appropriate).  For example, if there were
 TerminationIDs of R13/3/1, R13/3/2 and R13/3/3, the TerminationID
 R13/3/* would match all of them.  There are some circumstances where
 ALL Terminations must be referred to.  The TerminationID "*"
 suffices, and is referred to as ALL.  The CHOOSE TerminationID "$"
 may be used to signal to the MG that it has to create an ephemeral
 Termination or select an idle physical Termination.

B.2 ABNF specification

 The protocol syntax is presented in ABNF according to RFC 2234.
    Note 1 - This syntax specification does not enforce all
    restrictions on element inclusions and values.  Some additional
    restrictions are stated in comments and other restrictions appear
    in the text of this RFC.  These additional restrictions are part
    of the protocol even though not enforced by this specification.
    Note 2 - The syntax is context-dependent.  For example, "Add" can
    be the AddToken or a NAME depending on the context in which it
    occurs.
 Everything in the ABNF and text encoding is case insensitive.  This
 includes TerminationIDs, digitmap Ids etc.  SDP is case sensitive as
 per RFC 2327.
 ; NOTE -- The ABNF in this section uses the VALUE construct (or lists
 ; of VALUE constructs) to encode various package element values
 ; (properties, signal parameters, etc.).  The types of these values
 ; vary and are specified the relevant package definition.  Several
 ; such types are described in section 12.2.
 ;
 ; The ABNF specification for VALUE allows a quotedString form or a
 ; collection of SafeChars.  The encoding of package element values
 ; into ABNF VALUES is specified below.  If a type's encoding allows
 ; characters other than SafeChars, the quotedString form MUST be used
 ; for all values of that type, even for specific values that consist
 ; only of SafeChars.
 ;

Groves, et al. Standards Track [Page 113] RFC 3525 Gateway Control Protocol June 2003

 ; String:  A string MUST use the quotedString form of VALUE and can
 ; contain anything allowable in the quotedString form.
 ;
 ; Integer, Double, and Unsigned Integer:  Decimal values can be
 ; encoded using characters 0-9.  Hexadecimal values must be prefixed
 ; with '0x' and can use characters 0-9,a-f,A-F.  An octal format is
 ; not supported.  Negative integers start with '-' and MUST be
 ; Decimal.  The SafeChar form of VALUE MUST be used.
 ;
 ; Character:  A UTF-8 encoding of a single letter surrounded by
 ; double quotes.
 ;
 ; Enumeration:  An enumeration MUST use the SafeChar form of VALUE
 ; and can contain anything allowable in the SafeChar form.
 ;
 ; Boolean:  Boolean values are encoded as "on" and "off" and are
 ; case insensitive.  The SafeChar form of VALUE MUST be used.
 ;
 ; Future types:  Any defined types MUST fit within
 ; the ABNF specification of VALUE.  Specifically, if a type's
 ; encoding allows characters other than SafeChars, the quotedString
 ; form MUST be used for all values of that type, even for specific
 ; values that consist only of SafeChars.
 ;
 ; Note that there is no way to use the double quote character within
 ; a value.
 ;
 ; Note that SDP disallows whitespace at the beginning of a line,
 ; Megaco ABNF allows whitespace before the beginning of the SDP in
 ; the Local/Remote descriptor.  Parsers should accept whitespace
 ; between the LBRKT following the Local/Remote token and the
 ; beginning of the SDP.
 megacoMessage        = LWSP [authenticationHeader SEP ] message
 authenticationHeader = AuthToken EQUAL SecurityParmIndex COLON
                        SequenceNum COLON AuthData
 SecurityParmIndex    = "0x" 8(HEXDIG)
 SequenceNum          = "0x" 8(HEXDIG)
 AuthData             = "0x" 24*64(HEXDIG)
 message            = MegacopToken SLASH Version SEP mId SEP
 messageBody
 ; The version of the protocol defined here is equal to 1.
 messageBody          = ( errorDescriptor / transactionList )

Groves, et al. Standards Track [Page 114] RFC 3525 Gateway Control Protocol June 2003

 transactionList      = 1*( transactionRequest / transactionReply /
                        transactionPending / transactionResponseAck )
 ;Use of response acks is dependent on underlying transport
 transactionPending   = PendingToken EQUAL TransactionID LBRKT
 RBRKT
 transactionResponseAck = ResponseAckToken LBRKT transactionAck
                *(COMMA transactionAck) RBRKT
 transactionAck = transactionID / (transactionID "-" transactionID)
 transactionRequest   = TransToken EQUAL TransactionID LBRKT
                        actionRequest *(COMMA actionRequest) RBRKT
 actionRequest        = CtxToken EQUAL ContextID LBRKT ((
                        contextRequest [COMMA  commandRequestList])
                        / commandRequestList) RBRKT
 contextRequest    = ((contextProperties [COMMA contextAudit])
             / contextAudit)
 contextProperties    = contextProperty *(COMMA contextProperty)
 ; at-most-once
 contextProperty    = (topologyDescriptor / priority / EmergencyToken)
 contextAudit   = ContextAuditToken LBRKT contextAuditProperties
                       *(COMMA contextAuditProperties) RBRKT
 ; at-most-once
 contextAuditProperties = ( TopologyToken / EmergencyToken /
                            PriorityToken )
 ; "O-" indicates an optional command
 ; "W-" indicates a wildcarded response to a command
 commandRequestList = ["O-"] ["W-"] commandRequest
                      *(COMMA ["O-"] ["W-"]commandRequest)
 commandRequest      = ( ammRequest / subtractRequest / auditRequest /
                         notifyRequest / serviceChangeRequest)
 transactionReply     = ReplyToken EQUAL TransactionID LBRKT
                   [ ImmAckRequiredToken COMMA]
                 ( errorDescriptor / actionReplyList ) RBRKT
 actionReplyList      = actionReply *(COMMA actionReply )

Groves, et al. Standards Track [Page 115] RFC 3525 Gateway Control Protocol June 2003

 actionReply          = CtxToken EQUAL ContextID LBRKT
                   ( errorDescriptor / commandReply ) /
          (commandReply COMMA errorDescriptor) ) RBRKT
 commandReply      = (( contextProperties [COMMA commandReplyList] ) /
                         commandReplyList )
 commandReplyList     = commandReplys *(COMMA commandReplys )
 commandReplys        = (serviceChangeReply / auditReply / ammsReply /
                         notifyReply )
 ;Add Move and Modify have the same request parameters
 ammRequest           = (AddToken / MoveToken / ModifyToken ) EQUAL
                        TerminationID [LBRKT ammParameter *(COMMA
                        ammParameter) RBRKT]
 ;at-most-once
 ammParameter         = (mediaDescriptor / modemDescriptor /
                         muxDescriptor / eventsDescriptor /
                         signalsDescriptor / digitMapDescriptor /
                         eventBufferDescriptor / auditDescriptor)
 ammsReply            = (AddToken / MoveToken / ModifyToken /
                         SubtractToken ) EQUAL TerminationID [ LBRKT
                         terminationAudit RBRKT ]
 subtractRequest      =  SubtractToken EQUAL TerminationID
                         [ LBRKT auditDescriptor RBRKT]
 auditRequest         =  (AuditValueToken / AuditCapToken ) EQUAL
                         TerminationID LBRKT auditDescriptor RBRKT
 auditReply           = (AuditValueToken / AuditCapToken )
                        ( contextTerminationAudit  / auditOther)
 auditOther           = EQUAL TerminationID [LBRKT
                        terminationAudit RBRKT]
 terminationAudit = auditReturnParameter *(COMMA auditReturnParameter)
 contextTerminationAudit = EQUAL CtxToken ( terminationIDList /
                        LBRKT errorDescriptor RBRKT )
 auditReturnParameter = (mediaDescriptor / modemDescriptor /
                         muxDescriptor / eventsDescriptor /
                         signalsDescriptor / digitMapDescriptor /

Groves, et al. Standards Track [Page 116] RFC 3525 Gateway Control Protocol June 2003

                    observedEventsDescriptor / eventBufferDescriptor /
                         statisticsDescriptor / packagesDescriptor /
                          errorDescriptor / auditItem)
 auditDescriptor      = AuditToken LBRKT [ auditItem
                        *(COMMA auditItem) ] RBRKT
 notifyRequest        = NotifyToken EQUAL TerminationID
                        LBRKT ( observedEventsDescriptor
                              [ COMMA errorDescriptor ] ) RBRKT
 notifyReply          = NotifyToken EQUAL TerminationID
                        [ LBRKT errorDescriptor RBRKT ]
 serviceChangeRequest = ServiceChangeToken EQUAL TerminationID
                        LBRKT serviceChangeDescriptor RBRKT
 serviceChangeReply   = ServiceChangeToken EQUAL TerminationID
                        [LBRKT (errorDescriptor /
                        serviceChangeReplyDescriptor) RBRKT]
 errorDescriptor   = ErrorToken EQUAL ErrorCode
                     LBRKT [quotedString] RBRKT
 ErrorCode            = 1*4(DIGIT) ; could be extended
 TransactionID        = UINT32
 mId                  = (( domainAddress / domainName )
                        [":" portNumber]) / mtpAddress / deviceName
 ; ABNF allows two or more consecutive "." although it is meaningless
 ; in a domain name.
 domainName           = "<" (ALPHA / DIGIT) *63(ALPHA / DIGIT / "-" /
                        ".") ">"
 deviceName           = pathNAME
 ;The values 0x0, 0xFFFFFFFE and 0xFFFFFFFF are reserved.
 ContextID            = (UINT32 / "*" / "-" / "$")
 domainAddress        = "[" (IPv4address / IPv6address) "]"
 ;RFC2373 contains the definition of IP6Addresses.
 IPv6address          = hexpart [ ":" IPv4address ]
 IPv4address          = V4hex DOT V4hex DOT V4hex DOT V4hex
 V4hex                = 1*3(DIGIT) ; "0".."255"
 ; this production, while occurring in RFC2373, is not referenced
 ; IPv6prefix           = hexpart SLASH 1*2DIGIT
 hexpart           = hexseq "::" [ hexseq ] / "::" [ hexseq ] / hexseq

Groves, et al. Standards Track [Page 117] RFC 3525 Gateway Control Protocol June 2003

 hexseq               = hex4 *( ":" hex4)
 hex4                 = 1*4HEXDIG
 portNumber           = UINT16
 ; Addressing structure of mtpAddress:
 ; 25 - 15            0
 ;    |  PC        | NI |
 ;    24 - 14 bits    2 bits
 ; Note: 14 bits are defined for international use.
 ; Two national options exist where the point code is 16 or 24 bits.
 ; To octet align the mtpAddress the MSBs shall be encoded as 0s.
 ; An octet shall be represented by 2 hex digits.
 mtpAddress           = MTPToken LBRKT 4*8 (HEXDIG) RBRKT
 terminationIDList  = LBRKT TerminationID *(COMMA TerminationID) RBRKT
 ; Total length of pathNAME must not exceed 64 chars.
 pathNAME      = ["*"] NAME *("/" / "*"/ ALPHA / DIGIT /"_" / "$" )
                        ["@" pathDomainName ]
 ; ABNF allows two or more consecutive "." although it is meaningless
 ; in a path domain name.
 pathDomainName       = (ALPHA / DIGIT / "*" )
                        *63(ALPHA / DIGIT / "-" / "*" / ".")
 TerminationID        = "ROOT" / pathNAME / "$" / "*"
 mediaDescriptor = MediaToken LBRKT mediaParm *(COMMA mediaParm) RBRKT
 ; at-most one terminationStateDescriptor
 ; and either streamParm(s) or streamDescriptor(s) but not both
 mediaParm            = (streamParm / streamDescriptor /
                         terminationStateDescriptor)
 ; at-most-once per item
 streamParm           = ( localDescriptor / remoteDescriptor /
                         localControlDescriptor )
 streamDescriptor     = StreamToken EQUAL StreamID LBRKT streamParm
                        *(COMMA streamParm) RBRKT
 localControlDescriptor = LocalControlToken LBRKT localParm
                          *(COMMA localParm) RBRKT
 ; at-most-once per item except for propertyParm
 localParm = ( streamMode / propertyParm / reservedValueMode
                / reservedGroupMode )

Groves, et al. Standards Track [Page 118] RFC 3525 Gateway Control Protocol June 2003

 reservedValueMode    = ReservedValueToken EQUAL ( "ON" / "OFF" )
 reservedGroupMode    = ReservedGroupToken EQUAL ( "ON" / "OFF" )
 streamMode           = ModeToken EQUAL streamModes
 streamModes     = (SendonlyToken / RecvonlyToken / SendrecvToken /
                        InactiveToken / LoopbackToken )
 propertyParm         = pkgdName parmValue
 parmValue            = (EQUAL alternativeValue/ INEQUAL VALUE)
 alternativeValue     = ( VALUE
                / LSBRKT VALUE *(COMMA VALUE) RSBRKT
                 ; sublist (i.e., A AND B AND ...)
                / LBRKT VALUE *(COMMA VALUE) RBRKT
                 ; alternatives (i.e., A OR B OR ...)
                /  LSBRKT VALUE COLON VALUE RSBRKT )
                 ; range
 INEQUAL              = LWSP (">" / "<" / "#" ) LWSP
 LSBRKT               = LWSP "[" LWSP
 RSBRKT               = LWSP "]" LWSP
 ; Note - The octet zero is not among the permitted characters in
 ; octet string.  As the current definition is limited to SDP, and a
 ; zero octet would not be a legal character in SDP, this is not a
 ; concern.
 localDescriptor      = LocalToken LBRKT octetString RBRKT
 remoteDescriptor     = RemoteToken LBRKT octetString RBRKT
 eventBufferDescriptor= EventBufferToken [ LBRKT eventSpec
                        *( COMMA eventSpec) RBRKT ]
 eventSpec      = pkgdName [ LBRKT eventSpecParameter
              *(COMMA eventSpecParameter) RBRKT ]
 eventSpecParameter   = (eventStream / eventOther)
 eventBufferControl     = BufferToken EQUAL ( "OFF" / LockStepToken )
 terminationStateDescriptor = TerminationStateToken LBRKT
            terminationStateParm *( COMMA terminationStateParm ) RBRKT
 ; at-most-once per item except for propertyParm
 terminationStateParm = (propertyParm / serviceStates /
                         eventBufferControl )

Groves, et al. Standards Track [Page 119] RFC 3525 Gateway Control Protocol June 2003

 serviceStates        = ServiceStatesToken EQUAL ( TestToken /
                        OutOfSvcToken / InSvcToken )
 muxDescriptor        = MuxToken EQUAL MuxType  terminationIDList
 MuxType              = ( H221Token / H223Token / H226Token / V76Token
                         / extensionParameter )
 StreamID             = UINT16
 pkgdName     = (PackageName SLASH ItemID) ;specific item
              / (PackageName SLASH "*") ;all items in package
              / ("*" SLASH "*") ; all items supported by the MG
 PackageName          = NAME
 ItemID               = NAME
 eventsDescriptor     = EventsToken [ EQUAL RequestID LBRKT
                      requestedEvent *( COMMA requestedEvent ) RBRKT ]
 requestedEvent       = pkgdName [ LBRKT eventParameter
                        *( COMMA eventParameter ) RBRKT ]
 ; at-most-once each of KeepActiveToken , eventDM and eventStream
 ;at most one of either embedWithSig or embedNoSig but not both
 ;KeepActiveToken and embedWithSig must not both be present
 eventParameter       = ( embedWithSig / embedNoSig / KeepActiveToken
                          /eventDM / eventStream / eventOther )
 embedWithSig         = EmbedToken LBRKT signalsDescriptor
                          [COMMA embedFirst ] RBRKT
 embedNoSig        = EmbedToken LBRKT embedFirst RBRKT
 ; at-most-once of each
 embedFirst      = EventsToken [ EQUAL RequestID LBRKT
            secondRequestedEvent *(COMMA secondRequestedEvent) RBRKT ]
 secondRequestedEvent = pkgdName [ LBRKT secondEventParameter
                        *( COMMA secondEventParameter ) RBRKT ]
 ; at-most-once each of embedSig , KeepActiveToken, eventDM or
 ; eventStream
 ; KeepActiveToken and embedSig must not both be present
 secondEventParameter = ( embedSig / KeepActiveToken / eventDM /
                          eventStream / eventOther )
 embedSig  = EmbedToken LBRKT signalsDescriptor RBRKT
 eventStream          = StreamToken EQUAL StreamID

Groves, et al. Standards Track [Page 120] RFC 3525 Gateway Control Protocol June 2003

 eventOther           = eventParameterName parmValue
 eventParameterName   = NAME
 eventDM              = DigitMapToken EQUAL(( digitMapName ) /
                        (LBRKT digitMapValue RBRKT ))
 signalsDescriptor    = SignalsToken LBRKT [ signalParm
                        *(COMMA signalParm)] RBRKT
 signalParm           = signalList / signalRequest
 signalRequest        = signalName [ LBRKT sigParameter
                        *(COMMA sigParameter) RBRKT ]
 signalList           = SignalListToken EQUAL signalListId LBRKT
                        signalListParm *(COMMA signalListParm) RBRKT
 signalListId         = UINT16
 ;exactly once signalType, at most once duration and every signal
 ;parameter
 signalListParm       = signalRequest
 signalName           = pkgdName
 ;at-most-once sigStream, at-most-once sigSignalType,
 ;at-most-once sigDuration, every signalParameterName at most once
 sigParameter = sigStream / sigSignalType / sigDuration / sigOther
             / notifyCompletion / KeepActiveToken
 sigStream            = StreamToken EQUAL StreamID
 sigOther             = sigParameterName parmValue
 sigParameterName     = NAME
 sigSignalType        = SignalTypeToken EQUAL signalType
 signalType           = (OnOffToken / TimeOutToken / BriefToken)
 sigDuration          = DurationToken EQUAL UINT16
 notifyCompletion     = NotifyCompletionToken EQUAL (LBRKT
          notificationReason *(COMMA notificationReason) RBRKT)
 notificationReason   = ( TimeOutToken / InterruptByEventToken
                      / InterruptByNewSignalsDescrToken
                      / OtherReasonToken )
 observedEventsDescriptor = ObservedEventsToken EQUAL RequestID
                    LBRKT observedEvent *(COMMA observedEvent) RBRKT
 ;time per event, because it might be buffered
 observedEvent        = [ TimeStamp LWSP COLON] LWSP
                        pkgdName [ LBRKT observedEventParameter
                        *(COMMA observedEventParameter) RBRKT ]

Groves, et al. Standards Track [Page 121] RFC 3525 Gateway Control Protocol June 2003

 ;at-most-once eventStream, every eventParameterName at most once
 observedEventParameter = eventStream / eventOther
 ; For an AuditCapReply with all events, the RequestID should be ALL.
 RequestID            = ( UINT32 / "*" )
 modemDescriptor      = ModemToken (( EQUAL modemType) /
                    (LSBRKT modemType *(COMMA modemType) RSBRKT))
                   [ LBRKT propertyParm *(COMMA propertyParm) RBRKT ]
 ; at-most-once except for extensionParameter
 modemType            = (V32bisToken / V22bisToken / V18Token /
                         V22Token / V32Token / V34Token / V90Token /
                       V91Token / SynchISDNToken / extensionParameter)
 digitMapDescriptor  = DigitMapToken EQUAL
                      ( ( LBRKT digitMapValue RBRKT ) /
                      (digitMapName [ LBRKT digitMapValue RBRKT ]) )
 digitMapName        = NAME
 digitMapValue       = ["T" COLON Timer COMMA] ["S" COLON Timer COMMA]
                       ["L" COLON Timer COMMA] digitMap
 Timer               = 1*2DIGIT
 ; Units are seconds for T, S, and L timers, and hundreds of
 ; milliseconds for Z timer.  Thus T, S, and L range from 1 to 99
 ; seconds and Z from 100 ms to 9.9 s
 digitMap = (digitString /
             LWSP "(" LWSP digitStringList LWSP ")" LWSP)
 digitStringList   = digitString *( LWSP "|" LWSP digitString )
 digitString       = 1*(digitStringElement)
 digitStringElement = digitPosition [DOT]
 digitPosition     = digitMapLetter / digitMapRange
 digitMapRange     = ("x" / (LWSP "[" LWSP digitLetter LWSP "]" LWSP))
 digitLetter       = *((DIGIT "-" DIGIT ) / digitMapLetter)
 digitMapLetter    = DIGIT   ;Basic event symbols
             / %x41-4B / %x61-6B ; a-k, A-K
             / "L" / "S"   ;Inter-event timers (long, short)
             / "Z"         ;Long duration modifier
 ;at-most-once, and DigitMapToken and PackagesToken are not allowed
 ;in AuditCapabilities command
 auditItem            = ( MuxToken / ModemToken / MediaToken /
                         SignalsToken / EventBufferToken /
                         DigitMapToken / StatsToken / EventsToken /
                         ObservedEventsToken / PackagesToken )

Groves, et al. Standards Track [Page 122] RFC 3525 Gateway Control Protocol June 2003

 serviceChangeDescriptor = ServicesToken LBRKT serviceChangeParm
                          *(COMMA serviceChangeParm) RBRKT
 ; each parameter at-most-once
 ; at most one of either serviceChangeAddress or serviceChangeMgcId
 ; but not both
 ; serviceChangeMethod and serviceChangeReason are REQUIRED
 serviceChangeParm    = (serviceChangeMethod / serviceChangeReason /
                        serviceChangeDelay / serviceChangeAddress /
                        serviceChangeProfile / extension / TimeStamp /
                        serviceChangeMgcId / serviceChangeVersion )
 serviceChangeReplyDescriptor = ServicesToken LBRKT
                      servChgReplyParm *(COMMA servChgReplyParm) RBRKT
 ; at-most-once.  Version is REQUIRED on first ServiceChange response
 ; at most one of either serviceChangeAddress or serviceChangeMgcId
 ; but not both
 servChgReplyParm     = (serviceChangeAddress / serviceChangeMgcId /
                        serviceChangeProfile / serviceChangeVersion /
                        TimeStamp)
 serviceChangeMethod  = MethodToken EQUAL (FailoverToken /
                        ForcedToken / GracefulToken / RestartToken /
                        DisconnectedToken / HandOffToken /
                        extensionParameter)
 ; A serviceChangeReason consists of a numeric reason code
 ; and an optional text description.
 ; A serviceChangeReason MUST be encoded using the quotedString
 ; form of VALUE.
 ; The quotedString SHALL contain a decimal reason code,
 ; optionally followed by a single space character and a
 ; textual description string.
 serviceChangeReason  = ReasonToken  EQUAL VALUE
 serviceChangeDelay   = DelayToken   EQUAL UINT32
 serviceChangeAddress = ServiceChangeAddressToken EQUAL ( mId /
                        portNumber )
 serviceChangeMgcId   = MgcIdToken   EQUAL mId
 serviceChangeProfile = ProfileToken EQUAL NAME SLASH Version
 serviceChangeVersion = VersionToken EQUAL Version
 extension            = extensionParameter parmValue
 packagesDescriptor   = PackagesToken LBRKT packagesItem
                        *(COMMA packagesItem) RBRKT
 Version              = 1*2(DIGIT)
 packagesItem         = NAME "-" UINT16

Groves, et al. Standards Track [Page 123] RFC 3525 Gateway Control Protocol June 2003

 TimeStamp            = Date "T" Time ; per ISO 8601:1988
 ; Date = yyyymmdd
 Date                 = 8(DIGIT)
 ; Time = hhmmssss
 Time                 = 8(DIGIT)
 statisticsDescriptor = StatsToken LBRKT statisticsParameter
                       *(COMMA statisticsParameter ) RBRKT
 ;at-most-once per item
 statisticsParameter  = pkgdName [EQUAL VALUE]
 topologyDescriptor   = TopologyToken LBRKT topologyTriple
                        *(COMMA topologyTriple) RBRKT
 topologyTriple       = terminationA COMMA
                        terminationB COMMA topologyDirection
 terminationA         = TerminationID
 terminationB         = TerminationID
 topologyDirection    = BothwayToken / IsolateToken / OnewayToken
 priority             = PriorityToken EQUAL UINT16
 extensionParameter   = "X"  ("-" / "+") 1*6(ALPHA / DIGIT)
 ; octetString is used to describe SDP defined in RFC2327.
 ; Caution should be taken if CRLF in RFC2327 is used.
 ; To be safe, use EOL in this ABNF.
 ; Whenever "}" appears in SDP, it is escaped by "\", e.g., "\}"
 octetString          = *(nonEscapeChar)
 nonEscapeChar        = ( "\}" / %x01-7C / %x7E-FF )
 ; Note - The double-quote character is not allowed in quotedString.
 quotedString         = DQUOTE *(SafeChar / RestChar/ WSP) DQUOTE
 UINT16               = 1*5(DIGIT)  ; %x0-FFFF
 UINT32               = 1*10(DIGIT) ; %x0-FFFFFFFF
 NAME                 = ALPHA *63(ALPHA / DIGIT / "_" )
 VALUE                = quotedString / 1*(SafeChar)
 SafeChar             = DIGIT / ALPHA / "+" / "-" / "&" /
                        "!" / "_" / "/" / "\'" / "?" / "@" /
                        "^" / "`" / "~" / "*" / "$" / "\" /
                        "(" / ")" / "%" / "|" / "."
 EQUAL                = LWSP %x3D LWSP ; "="
 COLON                = %x3A           ; ":"
 LBRKT                = LWSP %x7B LWSP ; "{"
 RBRKT                = LWSP %x7D LWSP ; "}"
 COMMA                = LWSP %x2C LWSP ; ","

Groves, et al. Standards Track [Page 124] RFC 3525 Gateway Control Protocol June 2003

 DOT                  = %x2E           ; "."
 SLASH                = %x2F           ; "/"
 ALPHA                = %x41-5A / %x61-7A ; A-Z / a-z
 DIGIT                = %x30-39         ; 0-9
 DQUOTE               = %x22            ; " (Double Quote)
 HEXDIG               = ( DIGIT / "A" / "B" / "C" / "D" / "E" / "F" )
 SP                   = %x20        ; space
 HTAB                 = %x09        ; horizontal tab
 CR                   = %x0D        ; Carriage return
 LF                   = %x0A        ; linefeed
 LWSP                 = *( WSP / COMMENT / EOL )
 EOL                  = (CR [LF] / LF )
 WSP                  = SP / HTAB ; white space
 SEP                  = ( WSP / EOL / COMMENT) LWSP
 COMMENT              = ";" *(SafeChar/ RestChar / WSP / %x22) EOL
 RestChar            = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#" /
                        "<" / ">" / "="
 ; New Tokens added to sigParameter must take the format of SPA*
 ; * may be of any form i.e., SPAM
 ; New Tokens added to eventParameter must take the form of EPA*
 ; * may be of any form i.e., EPAD
 AddToken                   = ("Add"                   / "A")
 AuditToken                 = ("Audit"                 / "AT")
 AuditCapToken              = ("AuditCapability"       / "AC")
 AuditValueToken            = ("AuditValue"            / "AV")
 AuthToken                  = ("Authentication"        / "AU")
 BothwayToken               = ("Bothway"               / "BW")
 BriefToken                 = ("Brief"                 / "BR")
 BufferToken                = ("Buffer"                / "BF")
 CtxToken                   = ("Context"               / "C")
 ContextAuditToken       = ("ContextAudit"    / "CA")
 DigitMapToken              = ("DigitMap"              / "DM")
 DisconnectedToken          = ("Disconnected"          / "DC")
 DelayToken                 = ("Delay"                 / "DL")
 DurationToken              = ("Duration"              / "DR")
 EmbedToken                 = ("Embed"                 / "EM")
 EmergencyToken             = ("Emergency"             / "EG")
 ErrorToken                 = ("Error"                 / "ER")
 EventBufferToken           = ("EventBuffer"           / "EB")
 EventsToken                = ("Events"                / "E")
 FailoverToken              = ("Failover"              / "FL")
 ForcedToken                = ("Forced"                / "FO")
 GracefulToken              = ("Graceful"              / "GR")
 H221Token                  = ("H221" )
 H223Token                  = ("H223" )
 H226Token                  = ("H226" )

Groves, et al. Standards Track [Page 125] RFC 3525 Gateway Control Protocol June 2003

 HandOffToken               = ("HandOff"               / "HO")
 ImmAckRequiredToken        = ("ImmAckRequired"        / "IA")
 InactiveToken              = ("Inactive"              / "IN")
 IsolateToken               = ("Isolate"               / "IS")
 InSvcToken                 = ("InService"             / "IV")
 InterruptByEventToken      = ("IntByEvent"            / "IBE")
 InterruptByNewSignalsDescrToken
                            = ("IntBySigDescr"         / "IBS")
 KeepActiveToken            = ("KeepActive"            / "KA")
 LocalToken                 = ("Local"                 / "L")
 LocalControlToken          = ("LocalControl"          / "O")
 LockStepToken              = ("LockStep"              / "SP")
 LoopbackToken              = ("Loopback"              / "LB")
 MediaToken                 = ("Media"                 / "M")
 MegacopToken               = ("MEGACO"                / "!")
 MethodToken                = ("Method"                / "MT")
 MgcIdToken                 = ("MgcIdToTry"            / "MG")
 ModeToken                  = ("Mode"                  / "MO")
 ModifyToken                = ("Modify"                / "MF")
 ModemToken                 = ("Modem"                 / "MD")
 MoveToken                  = ("Move"                  / "MV")
 MTPToken                   = ("MTP")
 MuxToken                   = ("Mux"                   / "MX")
 NotifyToken                = ("Notify"                / "N")
 NotifyCompletionToken      = ("NotifyCompletion"      / "NC")
 ObservedEventsToken        = ("ObservedEvents"        / "OE")
 OnewayToken                = ("Oneway"                / "OW")
 OnOffToken                 = ("OnOff"                 / "OO")
 OtherReasonToken           = ("OtherReason"           / "OR")
 OutOfSvcToken              = ("OutOfService"          / "OS")
 PackagesToken              = ("Packages"              / "PG")
 PendingToken               = ("Pending"               / "PN")
 PriorityToken              = ("Priority"              / "PR")
 ProfileToken               = ("Profile"               / "PF")
 ReasonToken                = ("Reason"                / "RE")
 RecvonlyToken              = ("ReceiveOnly"           / "RC")
 ReplyToken                 = ("Reply"                 / "P")
 RestartToken               = ("Restart"               / "RS")
 RemoteToken                = ("Remote"                / "R")
 ReservedGroupToken         = ("ReservedGroup"         / "RG")
 ReservedValueToken         = ("ReservedValue"         / "RV")
 SendonlyToken              = ("SendOnly"              / "SO")
 SendrecvToken              = ("SendReceive"           / "SR")
 ServicesToken              = ("Services"              / "SV")
 ServiceStatesToken         = ("ServiceStates"         / "SI")
 ServiceChangeToken         = ("ServiceChange"         / "SC")
 ServiceChangeAddressToken  = ("ServiceChangeAddress"  / "AD")
 SignalListToken            = ("SignalList"            / "SL")

Groves, et al. Standards Track [Page 126] RFC 3525 Gateway Control Protocol June 2003

 SignalsToken               = ("Signals"               / "SG")
 SignalTypeToken            = ("SignalType"            / "SY")
 StatsToken                 = ("Statistics"            / "SA")
 StreamToken                = ("Stream"                / "ST")
 SubtractToken              = ("Subtract"              / "S")
 SynchISDNToken             = ("SynchISDN"             / "SN")
 TerminationStateToken      = ("TerminationState"      / "TS")
 TestToken                  = ("Test"                  / "TE")
 TimeOutToken               = ("TimeOut"               / "TO")
 TopologyToken              = ("Topology"              / "TP")
 TransToken                 = ("Transaction"           / "T")
 ResponseAckToken           = ("TransactionResponseAck" / "K")
 V18Token                   = ("V18")
 V22Token                   = ("V22")
 V22bisToken                = ("V22b")
 V32Token                   = ("V32")
 V32bisToken                = ("V32b")
 V34Token                   = ("V34")
 V76Token                   = ("V76")
 V90Token                   = ("V90")
 V91Token                   = ("V91")
 VersionToken               = ("Version"               / "V")

B.3 Hexadecimal octet coding

 Hexadecimal octet coding is a means for representing a string of
 octets as a string of hexadecimal digits, with two digits
 representing each octet.  This octet encoding should be used when
 encoding octet strings in the text version of the protocol.  For each
 octet, the 8-bit sequence is encoded as two hexadecimal digits.  Bit
 0 is the first transmitted; bit 7 is the last.  Bits 7-4 are encoded
 as the first hexadecimal digit, with Bit 7 as MSB and Bit 4 as LSB.
 Bits 3-0 are encoded as the second hexadecimal digit, with Bit 3 as
 MSB and Bit 0 as LSB. Examples:
      Octet bit pattern                   Hexadecimal coding
      00011011                            D8
      11100100                            27
      10000011 10100010 11001000 00001001 C1451390

B.4 Hexadecimal octet sequence

 A hexadecimal octet sequence is an even number of hexadecimal digits,
 terminated by a <CR> character.

Groves, et al. Standards Track [Page 127] RFC 3525 Gateway Control Protocol June 2003

ANNEX C - Tags for media stream properties

 Parameters for Local, Remote and LocalControl descriptors are
 specified as tag-value pairs if binary encoding is used for the
 protocol.  This annex contains the property names (PropertyID), the
 tags (Property tag), type of the property (Type) and the values
 (Value).  Values presented in the Value field when the field contains
 references shall be regarded as "information".  The reference
 contains the normative values.  If a value field does not contain a
 reference, then the values in that field can be considered as
 "normative".
 Tags are given as hexadecimal numbers in this annex.  When setting
 the value of a property, a MGC may underspecify the value according
 to one of the mechanisms specified in 7.1.1.
 It is optional to support the properties in this Annex or any of its
 sub-sections.  For example, only three properties from C.3 and only
 five properties from C.8 might be implemented.
 For type "enumeration" the value is represented by the value in
 brackets, e.g., Send(0), Receive(1).  Annex C properties with the
 types "N bits" or "M Octets" should be treated as octet strings when
 encoding the protocol.  Properties with "N bit integer" shall be
 treated as an integers.  "String" shall be treated as an IA5String
 when encoding the protocol.
 When a type is smaller than one octet, the value shall be stored in
 the low-order bits of an octet string of size 1.

C.1 General media attributes

 PropertyID    Property Type          Value
               tag
 Media         1001     Enumeration   Audio(0), Video(1), Data(2)
 Transmission  1002     Enumeration   Send(0), Receive(1),
 mode                                 Send&Receive(2)
 Number of     1003     Unsigned      0-255
 Channels               integer
 Sampling      1004     Unsigned      0-2^32
 rate                   integer
 Bitrate       1005     Integer       (0..4294967295)NOTE - Units of
                                      100 bit/s.

Groves, et al. Standards Track [Page 128] RFC 3525 Gateway Control Protocol June 2003

 ACodec        1006     Octet string  Audio Codec Type:
                                      Ref.: ITU-T Q.765
                                      Non-ITU-T codecs are defined
                                      with the appropriate standards
                                      organization under a defined
                                      Organizational Identifier.
 Samplepp      1007     Unsigned      Maximum samples or frames per
                        integer       packet: 0..65535
 Silencesupp   1008     Boolean       Silence Suppression: True/False
 Encrypttype   1009     Octet string  Ref.: ITU-T H.245
 Encryptkey    100A     Octet string  Encryption key
                        size          Ref.: ITU-T H.235
                        (0..65535)
 Echocanc      100B                    Not Used.  See H.248.1 E.13 for
                                      an example of possible Echo
                                      Control properties.
 Gain          100C     Unsigned      Gain in dB: 0..65535
                        integer
 Jitterbuff    100D     Unsigned      Jitter buffer size in ms:
                        integer       0..65535
 PropDelay     100E     Unsigned      Propagation Delay: 0..65535
                        integer       Maximum propagation delay in
                                      milliseconds for the bearer
                                      connection between two media
                                      gateways.  The maximum delay
                                      will be dependent on the bearer
                                      technology.
 RTPpayload    100F     Integer       Payload type in RTP Profile for
                                      Audio and Video Conferences
                                      with Minimal Control
                                      Ref.: RFC 1890

Groves, et al. Standards Track [Page 129] RFC 3525 Gateway Control Protocol June 2003

C.2 Mux properties

 PropertyID Property tag Type         Value
 H222       2001         Octet string H222LogicalChannelParameters
                                       Ref.: ITU-T H.245
 H223       2002         Octet string H223LogicalChannelParameters
                                       Ref.: ITU-T H.245
 V76        2003         Octet string V76LogicalChannelParameters
                                       Ref.: ITU-T H.245
 H2250      2004         Octet string H2250LogicalChannelParameters
                                       Ref.: ITU-T H.245

C.3 General bearer properties

 PropertyID Property   Type        Value
            tag
 Mediatx    3001       Enumeration Media Transport TypeTDM
                                    Circuit(0), ATM(1), FR(2),
                                    Ipv4(3), Ipv6(4), ...
 BIR        3002       4 octets    Value depends on transport
                                    technology
 NSAP       3003       1-20 octets See NSAP.
                                    Ref.: Annex A/X.213

C.4 General ATM properties

 PropertyID Property Type              Value
            tag
 AESA       4001     20 octets         ATM End System Address
 VPVC       4002     4 octets: VPCI    VPCI/VCI
                      in first two
                      least             Ref.: ITU-T Q.2931
                      significant
                      octets, VCI in
                      second two
                      octets

Groves, et al. Standards Track [Page 130] RFC 3525 Gateway Control Protocol June 2003

 SC         4003     Enumeration       Service Category: CBR(0),
                                        nrt-VBR1(1), nrt  VBR2(2),
                                        nrt-VBR3(3), rt-VBR1(4),
                                        rt  VBR2(5), rt-VBR3(6),
                                        UBR1(7), UBR2(8), ABR(9).
                                        Ref.: ATM Forum UNI 4.0
 BCOB       4004     5-bit integer     Broadband Bearer Class
                                        Ref.: ITU-T Q.2961.2
 BBTC       4005     7-bit integer     Broadband Transfer Capability
                                        Ref.: ITU-T Q.2961.1
 ATC        4006     Enumeration       I.371 ATM Traffic
                                        CapabilityDBR(0), SBR1(1),
                                        SBR2(2), SBR3(3), ABT/IT(4),
                                        ABT/DT(5), ABR(6)
                                        Ref.: ITU-T I.371
 STC        4007     2 bits            Susceptibility to clipping:
                                        Bits
                                        2 1
                                        ---
                                        0 0     not susceptible to
                                                clipping
                                        0 1     susceptible to
                                                clipping
                                        Ref.: ITU-T Q.2931
 UPCC       4008     2 bits            User Plane Connection
                                        configuration:
                                        Bits
                                        2 1
                                        ---
                                        0 0     point-to-point
                                        0 1     point-to-multipoint
                                        Ref.: ITU-T Q.2931
 PCR0       4009     24-bit integer    Peak Cell Rate (For CLP = 0)
                                        Ref.: ITU-T Q.2931
 SCR0       400A     24-bit integer    Sustainable Cell Rate (For
                                        CLP = 0)
                                        Ref.: ITU-T Q.2961.1
 MBS0       400B     24-bit integer    Maximum Burst Size (For CLP =
                                        0)
                                        Ref.: ITU-T Q.2961.1

Groves, et al. Standards Track [Page 131] RFC 3525 Gateway Control Protocol June 2003

 PCR1       400C     24-bit integer    Peak Cell Rate (For CLP = 0 +
                                        1)
                                        Ref.: ITU-T Q.2931
 SCR1       400D     24-bit integer    Sustainable Cell Rate (For
                                        CLP = 0 + 1)
                                        Ref.: ITU-T Q.2961.1
 MBS1       400E     24-bit integer    Maximum Burst Size (For CLP =
                                        0 + 1)
                                        Ref.: ITU-T Q.2961.1
 BEI        400F     Boolean           Best Effort Indicator
                                        Value 1 indicates that BEI is
                                        to be included in the ATM
                                        signaling; value 0 indicates
                                        that BEI is not to be
                                        included in the ATM
                                        signaling.
                                        Ref.: ATM Forum UNI 4.0
 TI         4010     Boolean           Tagging Indicator
                                        Value 0 indicates that
                                        tagging is not allowed; value
                                        1 indicates that tagging is
                                        requested.
                                        Ref.: ITU-T Q.2961.1
 FD         4011     Boolean           Frame Discard
                                        Value 0 indicates that no
                                        frame discard is allowed;
                                        value 1 indicates that frame
                                        discard is allowed.
                                        Ref.: ATM Forum UNI 4.0
 A2PCDV     4012     24-bit integer    Acceptable 2-point CDV
                                        Ref.: ITU-T Q.2965.2
 C2PCDV     4013     24-bit integer    Cumulative 2-point CDV
                                        Ref.: ITU-T Q.2965.2
 APPCDV     4014     24-bit integer    Acceptable P-P CDV
                                        Ref.: ATM Forum UNI 4.0
 CPPCDV     4015     24-bit integer    Cumulative P-P CDV
                                        Ref.: ATM Forum UNI 4.0

Groves, et al. Standards Track [Page 132] RFC 3525 Gateway Control Protocol June 2003

 ACLR       4016     8-bit integer     Acceptable Cell Loss Ratio
                                        Ref.: ITU-T Q.2965.2, ATM
                                        Forum UNI 4.0
 MEETD      4017     16-bit integer    Maximum End-to-end transit
                                        delay
                                        Ref.: ITU-T Q.2965.2, ATM
                                        Forum UNI 4.0
 CEETD      4018     16-bit integer    Cumulative End-to-end transit
                                        delay
                                        Ref.: ITU-T Q.2965.2, ATM
                                        Forum UNI 4.0
 QosClass   4019     Integer 0-5          QoS Class
                                          QoS Class     Meaning
                                          0             Default QoS
                                                         associated
                                                         with the ATC
                                                         as defined
                                                         in ITU-T
                                                         Q.2961.2
                                          1             Stringent
                                          2             Tolerant
                                          3             Bi-level
                                          4             Unbounded
                                          5             Stringent
                                                         Bi-level
                                        Ref.: ITU-T Q.2965.1
 AALtype    401A     1 octet           AAL Type
                                        Bits
                                        8 7 6 5 4 3 2 1
                                        ---------------
                                        0 0 0 0 0 0 0 0   AAL for
                                                          voice
                                        0 0 0 0 0 0 0 1   AAL type 1
                                        0 0 0 0 0 0 1 0   AAL type 2
                                        0 0 0 0 0 0 1 1   AAL type
                                                          3/4
                                        0 0 0 0 0 1 0 1   AAL type 5

Groves, et al. Standards Track [Page 133] RFC 3525 Gateway Control Protocol June 2003

                                        0 0 0 1 0 0 0 0   user-
                                                          defined AAL
                                        Ref.: ITU-T Q.2931

C.5 Frame Relay

 PropertyID         Property    Type          Value
                    tag
 DLCI               5001        Unsigned      Data link connection
                                integer       id
 CID                5002        Unsigned      sub-channel id
                                integer
 SID/Noiselevel     5003        Unsigned      silence insertion
                                integer       descriptor
 Primary Payload    5004        Unsigned      Primary Payload Type
 type                           integer       Covers FAX and codecs

C.6 IP

 PropertyID Property tag Type                Value
 IPv4       6001         32 bits Ipv4Address Ipv4Address
                                              Ref.: IETF RFC 791
 IPv6       6002         128 bits            IPv6 Address
                                              Ref.: IETF RFC 2460
 Port       6003         Unsigned integer    0..65535
 Porttype   6004         Enumerated          TCP(0), UDP(1), SCTP(2)

C.7 ATM AAL2

 PropertyID Property Type                   Value
            tag
 AESA       7001     20 octets              AAL2 service endpoint
                                              address as defined in
                                              the referenced
                                              Recommendation.
                                              ESEANSEA
                                              Ref.: ITU-T Q.2630.1

Groves, et al. Standards Track [Page 134] RFC 3525 Gateway Control Protocol June 2003

 BIR        See C.3  4 octets               Served user generated
                                              reference as defined in
                                              the referenced
                                              Recommendation.
                                              SUGR
                                              Ref.: ITU-T Q.2630.1
 ALC        7002     12 octets              AAL2 link
                                              characteristics as
                                              defined in the
                                              referenced
                                              Recommendation.
                                              Maximum/Average CPS-SDU
                                              bit rate;
                                              Maximum/Average CPS-SDU
                                              size
                                              Ref.: ITU-T Q.2630.1
 SSCS       7003     I.366.2: Audio (8      Service specific
                      octets); Multirate (3  convergence sublayer
                      octets), or I.366.1:   information as defined
                      SAR-assured (14        in:
                      octets);SAR-unassured  - ITU-T Q.2630.1,and
                      (7 octets).            used in:
                                              - ITU-T I.366.2:
                                              Audio/Multirate;
                                              - ITU-T I.366.1: SAR-
                                              assured/unassured.
                                              Ref.: ITU-T Q.2630.1,
                                              I.366.1 and I.366.2
 SUT        7004     1..254 octets          Served user transport
                                              parameter as defined in
                                              the referenced
                                              Recommendation.
                                              Ref.: ITU-T Q.2630.1
 TCI        7005     Boolean                Test connection
                                              indicator as defined in
                                              the referenced
                                              Recommendation.
                                              Ref.: ITU-T Q.2630.1
 Timer_CU   7006     32-bit integer         Timer-CU
                                              Milliseconds to hold
                                              partially filled cell
                                              before sending.

Groves, et al. Standards Track [Page 135] RFC 3525 Gateway Control Protocol June 2003

 MaxCPSSDU  7007     8-bit integer          Maximum Common Part
                                              Sublayer Service Data
                                              Unit
                                              Ref.: ITU-T Q.2630.1
 CID        7008     8 bits                 subchannel id: 0-255
                                              Ref.: ITU-T I.363.2

C.8 ATM AAL1

 PropertyID Property   Type        Value
            tag
 BIR        See table  4-29 octets GIT (Generic Identifier
            in C.3                 Transport)
                                    Ref.: ITU-T Q.2941.1
 AAL1ST     8001       1 octet     AAL1 Subtype
                                    Bits
                                    8 7 6 5 4 3 2 1
                                    ---------------
                                    0 0 0 0 0 0 0 0     null
                                    0 0 0 0 0 0 0 1     voiceband
                                    signal transport on 64 kbit/s
                                    0 0 0 0 0 0 1 0     circuit
                                    transport
                                    0 0 0 0 0 1 0 0     high-quality
                                    audio signal transport
                                    0 0 0 0 0 1 0 1     video signal
                                    transport
                                    Ref.: ITU-T Q.2931
 CBRR       8002       1 octet     CBR Rate
                                    Bits
                                    8 7 6 5 4 3 2 1
                                    ---------------
                                    0 0 0 0 0 0 0 1       64 kbit/s
                                    0 0 0 0 0 1 0 0     1544 kbit/s
                                    0 0 0 0 0 1 0 1     6312 kbit/s
                                    0 0 0 0 0 1 1 0   32 064 kbit/s
                                    0 0 0 0 0 1 1 1   44 736 kbit/s
                                    0 0 0 0 1 0 0 0   97 728 kbit/s
                                    0 0 0 1 0 0 0 0     2048 kbit/s
                                    0 0 0 1 0 0 0 1     8448 kbit/s
                                    0 0 0 1 0 0 1 0   34 368 kbit/s
                                    0 0 0 1 0 0 1 1  139 264 kbit/s
                                    0 1 0 0 0 0 0 0   n x 64 kbit/s
                                    0 1 0 0 0 0 0 1    n x 8 kbit/s
                                    Ref.: ITU-T Q.2931

Groves, et al. Standards Track [Page 136] RFC 3525 Gateway Control Protocol June 2003

 MULT       See table              Multiplier, or n x 64k/8k/300
            in C.9                 Ref.: ITU-T Q.2931
 SCRI       8003       1 octet     Source Clock Frequency Recovery
                                    Method
                                    Bits
                                    8 7 6 5 4 3 2 1
                                    ---------------
                                    0 0 0 0 0 0 0 0     null
                                    0 0 0 0 0 0 0 1     SRTS
                                    0 0 0 0 0 0 1 0     ACM
                                    Ref.: ITU-T Q.2931
 ECM        8004       1 octet     Error Correction Method
                                    Bits
                                    8 7 6 5 4 3 2 1
                                    ---------------
                                    0 0 0 0 0 0 0 0     null
                                    0 0 0 0 0 0 0 1     FEC - Loss
                                    0 0 0 0 0 0 1 0     FEC - Delay
                                    Ref.: ITU-T Q.2931
 SDTB       8005       16-bit      Structured Data Transfer
                       integer     Blocksize
                                    Block size of SDT CBR service
                                    Ref.: ITU-T I.363.1
 PFCI       8006       8-bit       Partially filled cells identifier
                       integer     1-47
                                    Ref.: ITU-T I.363.1

C.9 Bearer capabilities

 The table entries referencing Recommendation Q.931 refer to the
 encoding in the bearer capability information element of Q.931, not
 to the low layer information element.
 PropertyID    Tag    Type      Value
 TMR           9001   1 octet   Transmission Medium
                                Requirement (Q.763)
                                Bits
                                87654321
                                --------
                                00000000  speech
                                00000001  spare
                                00000010  64 kbit/s
                                unrestricted

Groves, et al. Standards Track [Page 137] RFC 3525 Gateway Control Protocol June 2003

                                00000011  3.1 kHz audio
                                00000100  reserved for
                                alternate speech (service
                                2)/64 kbit/s unrestricted
                                (service 1)
                                00000101  reserved for
                                alternate 64 kbit/s
                                unrestricted (service
                                1)/speech (service 2)
                                00000110  64 kbit/s preferred
                                The assigned codepoints
                                listed below are all for
                                unrestricted service.
                                00000111  2 x 64 kbit/s
                                00001000  384 kbit/s
                                00001001  1536 kbit/s
                                00001010  1920 kbit/s
                                00001011
                                 through
                                00001111  spare
                                00010000
                                 through
                                00101010:
                                   3 x 64 kbit/s through
                                  29 x 64 kbit/s
                                except
                                00010011  spare
                                00100101  spare
                                00101011
                                 through
                                11111111  spare
                                Ref.: ITU-T Q.763
 TMRSR         9002   1 octet   Transmission Medium
                                Requirement Subrate
                                0     unspecified
                                1      8 kbit/s
                                2     16 kbit/s
                                3     32 kbit/s
 Contcheck     9003   Boolean   Continuity Check
                                0     continuity check not
                                required on this circuit
                                1     continuity check
                                required on this circuit
                                Ref.: ITU-T Q.763

Groves, et al. Standards Track [Page 138] RFC 3525 Gateway Control Protocol June 2003

 ITC           9004   5 bits    Information Transfer
                                Capability
                                Bits
                                5 4 3 2 1
                                ---------
                                0 0 0 0 0     Speech
                                0 1 0 0 0     Unrestricted
                                digital information
                                0 1 0 0 1     Restricted
                                digital information
                                1 0 0 0 0     3.1 kHz audio
                                1 0 0 0 1     Unrestricted
                                digital information with
                                tones/announcements
                                1 1 0 0 0     Video
                                All other values are
                                reserved.
                                Ref.: ITU-T Q.763
 TransMode     9005   2 bits    Transfer Mode
                                Bits
                                2 1
                                ---
                                0 0     Circuit mode
                                1 0     Packet mode
                                Ref.: ITU-T Q.931
 TransRate     9006   5 bits    Transfer Rate
                                Bits
                                5 4 3 2 1
                                ---------
                                0 0 0 0 0     This code shall
                                be used for packet mode calls
                                1 0 0 0 0      64 kbit/s
                                1 0 0 0 1  2 x 64 kbit/s
                                1 0 0 1 1     384 kbit/s
                                1 0 1 0 1    1536 kbit/s
                                1 0 1 1 1    1920 kbit/s
                                1 1 0 0 0  Multirate (64
                                kbit/s base rate)
                                Ref.: ITU-T Q.931
 MULT          9007   7 bits    Rate Multiplier
                                Any value from 2 to n
                                (maximum number of B-
                                channels)
                                Ref.: ITU-T Q.931

Groves, et al. Standards Track [Page 139] RFC 3525 Gateway Control Protocol June 2003

 layer1prot    9008   5 bits    User Information Layer 1
                                Protocol
                                Bits
                                5 4 3 2 1
                                ---------
                                0 0 0 0 1     ITU-T
                                standardized rate adaption
                                V.110 and X.30.
                                0 0 0 1 0     Recommendation
                                G.711 m-law
                                0 0 0 1 1     Recommendation
                                G.711 A-law
                                0 0 1 0 0     Recommendation
                                G.721 32 kbit/s ADPCM and
                                Recommendation I.460
                                0 0 1 0 1     Recommendations
                                H.221 and H.242
                                0 0 1 1 0     Recommendations
                                H.223 and H.245
                                0 0 1 1 1     Non-ITU-T
                                standardized rate adaption.
                                0 1 0 0 0     ITU-T
                                standardized rate adaption
                                V.120.
                                0 1 0 0 1     ITU-T
                                standardized rate adaption
                                X.31 HDLC flag stuffing
                                All other values are
                                reserved.
                                Ref.: ITU Recommendation
                                Q.931
 syncasync     9009   Boolean   Synchronous/Asynchronous
                                0     Synchronous data
                                1     Asynchronous data
                                Ref.: ITU-T Q.931
 negotiation   900A   Boolean   Negotiation
                                0     In-band negotiation
                                possible
                                1     In-band negotiation not
                                possible
                                Ref.: ITU-T Q.931
 Userrate      900B   5 bits    User Rate
                                Bits
                                5 4 3 2 1

Groves, et al. Standards Track [Page 140] RFC 3525 Gateway Control Protocol June 2003

  1. ——–

0 0 0 0 0 Rate is

                                indicated by E-bits specified
                                in Recommendation I.460 or
                                may be negotiated in-band
                                0 0 0 0 1     0.6 kbit/s
                                Recommendations V.6 and X.1
                                0 0 0 1 0     1.2 kbit/s
                                Recommendation V.6
                                0 0 0 1 1     2.4 kbit/s
                                Recommendations V.6 and X.1
                                0 0 1 0 0     3.6 kbit/s
                                Recommendation V.6
                                0 0 1 0 1     4.8 kbit/s
                                Recommendations V.6 and X.1
                                0 0 1 1 0     7.2 kbit/s
                                Recommendation V.6
                                0 0 1 1 1     8 kbit/s
                                Recommendation I.460
                                0 1 0 0 0     9.6 kbit/s
                                Recommendations V.6 and X.1
                                0 1 0 0 1     14.4 kbit/s
                                Recommendation V.6
                                0 1 0 1 0     16 kbit/s
                                Recommendation I.460
                                0 1 0 1 1     19.2 kbit/s
                                Recommendation V.6
                                0 1 1 0 0     32 kbit/s
                                Recommendation I.460
                                0 1 1 0 1     38.4 kbit/s
                                Recommendation V.110
                                0 1 1 1 0     48 kbit/s
                                Recommendations V.6 and X.1
                                0 1 1 1 1     56 kbit/s
                                Recommendation V.6
                                1 0 0 1 0     57.6 kbit/s
                                Recommendation V.14 extended
                                1 0 0 1 1     28.8 kbit/s
                                Recommendation V.110
                                1 0 1 0 0     24 kbit/s
                                Recommendation V.110
                                1 0 1 0 1     0.1345 kbit/s
                                Recommendation X.1
                                1 0 1 1 0     0.100 kbit/s
                                Recommendation X.1
                                1 0 1 1 1     0.075/1.2
                                kbit/s Recommendations V.6
                                and X.1

Groves, et al. Standards Track [Page 141] RFC 3525 Gateway Control Protocol June 2003

                                1 1 0 0 0     1.2/0.075
                                kbit/s Recommendations V.6
                                and X.1
                                1 1 0 0 1     0.050 kbit/s
                                Recommendations V.6 and X.1
                                1 1 0 1 0     0.075 kbit/s
                                Recommendations V.6 and X.1
                                1 1 0 1 1     0.110 kbit/s
                                Recommendations V.6 and X.1
                                1 1 1 0 0     0.150 kbit/s
                                Recommendations V.6 and X.1
                                1 1 1 0 1     0.200 kbit/s
                                Recommendations V.6 and X.1
                                1 1 1 1 0     0.300 kbit/s
                                Recommendations V.6 and X.1
                                1 1 1 1 1     12 kbit/s
                                Recommendation V.6
                                All other values are
                                reserved.
                                Ref.: ITU-T Q.931
 INTRATE       900C   2 bits    Intermediate Rate
                                Bits
                                2 1
                                ---
                                0 0     Not used
                                0 1     8 kbit/s
                                1 0     16 kbit/s
                                1 1     32 kbit/s
                                Ref.: ITU-T Q.931
 nictx         900D   Boolean   Network Independent Clock
                                (NIC) on transmission
                                0     Not required to send
                                data with network independent
                                clock
                                1     Required to send data
                                with network independent
                                clock
                                Ref.: ITU-T Q.931
 nicrx         900E   Boolean   Network independent clock
                                (NIC) on reception
                                0     Cannot accept data with
                                network independent clock
                                (i.e., sender does not support
                                this optional procedure)
                                1     Can accept data with
                                network independent clock

Groves, et al. Standards Track [Page 142] RFC 3525 Gateway Control Protocol June 2003

                                (i.e., sender does support
                                this optional procedure)
                                Ref.: ITU-T Q.931
 flowconttx    900F   Boolean   Flow Control on transmission
                                (Tx)
                                0     Not required to send
                                data with flow control
                                mechanism
                                1     Required to send data
                                with flow control mechanism
                                Ref.: ITU-T Q.931
 flowcontrx    9010   Boolean   Flow control on reception
                                (Rx)
                                0     Cannot accept data with
                                flow control mechanism (i.e.,
                                sender does not support this
                                optional procedure)
                                1     Can accept data with
                                flow control mechanism (i.e.,
                                sender does support this
                                optional procedure)
                                Ref.: ITU-T Q.931
 rateadapthdr  9011   Boolean   Rate adaption header/no
                                header
                                0     Rate adaption header
                                not included
                                1     Rate adaption header
                                included
                                Ref.: ITU-T Q.931
 multiframe    9012   Boolean   Multiple frame establishment
                                support in data link
                                0     Multiple frame
                                establishment not supported.
                                Only UI frames allowed
                                1     Multiple frame
                                establishment supported
                                Ref.: ITU-T Q.931
 OPMODE        9013   Boolean   Mode of operation
                                0     Bit transparent mode of
                                operation
                                1     Protocol sensitive mode
                                of operation
                                Ref.: ITU-T Q.931

Groves, et al. Standards Track [Page 143] RFC 3525 Gateway Control Protocol June 2003

 llidnegot     9014   Boolean   Logical link identifier
                                negotiation
                                0     Default, LLI = 256 only
                                1     Full protocol
                                negotiation
                                Ref.: ITU-T Q.931
 assign        9015   Boolean   Assignor/assignee
                                0     Message originator is
                                "default assignee"
                                1     Message originator is
                                "assignor only"
                                Ref.: ITU-T Q.931
 inbandneg     9016   Boolean   In-band/out-band negotiation
                                0     Negotiation is done
                                with USER INFORMATION
                                messages on a temporary
                                signalling connection
                                1     Negotiation is done in-
                                band using logical link zero
                                Ref.: ITU-T Q.931
 stopbits      9017   2 bits    Number of stop bits
                                Bits
                                2 1
                                ---
                                0 0     Not used
                                0 1     1 bit
                                1 0     1.5 bits
                                1 1     2 bits
                                Ref.: ITU-T Q.931
 databits      9018   2 bits    Number of data bits excluding
                                parity bit if present
                                Bits
                                2 1
                                ---
                                0 0     Not used
                                0 1     5 bits
                                1 0     7 bits
                                1 1     8 bits
                                Ref.: ITU-T Q.931
 parity        9019   3 bits    Parity information
                                Bits
                                3 2 1

Groves, et al. Standards Track [Page 144] RFC 3525 Gateway Control Protocol June 2003

  1. —–

0 0 0 Odd

                                0 1 0     Even
                                0 1 1     None
                                1 0 0     Forced to 0
                                1 0 1     Forced to 1
                                All other values are
                                reserved.
                                Ref.: ITU-T Q.931
 duplexmode    901A   Boolean   Mode duplex
                                0     Half duplex
                                1     Full duplex
                                Ref.: ITU-T Q.931
 modem         901B   6 bits    Modem Type
                                Bits
                                6 5 4 3 2 1
                                -----------
                                0 0 0 0 0 0 through
                                0 0 0 1 0 1   National use
                                0 1 0 0 0 1   Rec.  V.21
                                0 1 0 0 1 0     Rec.  V.22
                                0 1 0 0 1 1     Rec.  V.22 bis
                                0 1 0 1 0 0     Rec.  V.23
                                0 1 0 1 0 1     Rec.  V.26
                                0 1 1 0 0 1     Rec.  V.26 bis
                                0 1 0 1 1 1     Rec.  V.26 ter
                                0 1 1 0 0 0     Rec.  V.27
                                0 1 1 0 0 1     Rec.  V.27 bis
                                0 1 1 0 1 0     Rec.  V.27 ter
                                0 1 1 0 1 1     Rec.  V.29
                                0 1 1 1 0 1     Rec.  V.32
                                0 1 1 1 1 0     Rec.  V.34
                                1 0 0 0 0 0  through
                                1 0 1 1 1 1    National use
                                1 1 0 0 0 0  through
                                1 1 1 1 1 1    User specified
                                Ref.: ITU-T Q.931
 layer2prot    901C   5 bits    User information layer 2
                                protocol
                                Bits
                                5 4 3 2 1
                                ---------
                                0 0 0 1 0    Rec.  Q.921/I.441
                                0 0 1 1 0    Rec.  X.25, link
                                layer

Groves, et al. Standards Track [Page 145] RFC 3525 Gateway Control Protocol June 2003

                                0 1 1 0 0    LAN logical link
                                control (ISO/IEC 8802  2)
                                All other values are
                                reserved.
                                Ref.: ITU-T Q.931
 layer3prot    901D   5 bits    User information layer 3
                                protocol
                                Bits
                                5 4 3 2 1
                                ---------
                                0 0 0 1 0     ITU-T Q.931
                                0 0 1 1 0     ITU-T X.25,
                                packet layer
                                0 1 0 1 1     ISO/IEC TR 9577
                                (Protocol identification in
                                the network layer)
                                All other values are
                                reserved.
                                Ref.: ITU-T Q.931
 addlayer3prot 901E   Octet     Additional User Information
                                layer 3 protocol
                                Bits        Bits
                                4 3 2 1     4 3 2 1
                                -------     -------
                                1 1 0 0     1 1 0 0
                                Internet Protocol (RFC 791)
                                (ISO/IEC TR 9577)
                                1 1 0 0     1 1 1 1
                                Point-to-point Protocol (RFC
                                1661)
                                Ref.: ITU-T Q.931
 DialledN      901F   30        Dialled Number
                      octets
 DiallingN     9020   30        Dialling Number
                      octets
 ECHOCI        9021             Not Used.  See H.248.1 E.13
                                for an example of possible
                                Echo Control properties.
 NCI           9022   1 octet   Nature of Connection
                                Indicators
                                Bits
                                2 1     Satellite Indicator

Groves, et al. Standards Track [Page 146] RFC 3525 Gateway Control Protocol June 2003

0 0 no satellite circuit

                                in the connection
                                0 1     one satellite circuit
                                in the connection
                                1 0     two satellite
                                circuits in the connection
                                1 1     spare
                                Bits
                                4 3     Continuity check
                                ---     indicator
                                0 0     continuity check not
                                required
                                0 1     continuity check
                                required on this circuit
                                1 0     continuity check
                                performed on a previous
                                circuit
                                1 1     spare
                                Bit
                                5     Echo control device
                                -     indicator
                                0     outgoing echo control
                                device not included
                                1     outgoing echo control
                                device included
                                Bits
                                8 7 6     Spare
                                Ref.: ITU-T Q.763
 USI           9023   Octet     User Service Information
                      string    Ref.: ITU-T Q.763 Clause 3.57

C.10 AAL5 properties

 PropertyID Property    Type       Value
            tag
 FMSDU      A001        32-bit     Forward Maximum CPCS-SDU Size:
                        integer    Maximum CPCS-SDU size sent in the
                                   direction from the calling user to
                                   the called user.
                                   Ref.: ITU-T Q.2931

Groves, et al. Standards Track [Page 147] RFC 3525 Gateway Control Protocol June 2003

 BMSDU      A002        32-bit     Backwards Maximum CPCS-SDU Size:
                        integer    Maximum CPCS-SDU size sent in the
                                   direction from the called user to
                                   the calling user.
                                   Ref.: ITU-T Q.2931
 SSCS       See table   See table  See table in C.7
            in C.7      in C.7     Additional values:
                                   VPI/VCI

C.11 SDP equivalents

 PropertyID Property    Type   Value
            tag
 SDP_V      B001        String Protocol Version
                                Ref.: RFC 2327
 SDP_O      B002        String Owner/creator and session ID
                                Ref.: RFC 2327
 SDP_S      B003        String Session name
                                Ref.: RFC 2327
 SDP_I      B004        String Session identifier
                                Ref.: RFC 2327
 SDP_U      B005        String URI of descriptor
                                Ref.: RFC 2327
 SDC_E      B006        String email address
                                Ref.: RFC 2327
 SDP_P      B007        String phone number
                                Ref.: RFC 2327
 SDP_C      B008        String Connection information
                                Ref.: RFC 2327
 SDP_B      B009        String Bandwidth Information
                                Ref.: RFC 2327
 SDP_Z      B00A        String Time zone adjustment
                                Ref.: RFC 2327
 SDP_K      B00B        String Encryption Key
                                Ref.: RFC 2327

Groves, et al. Standards Track [Page 148] RFC 3525 Gateway Control Protocol June 2003

 SDP_A      B00C        String Zero or more session attributes
                                Ref.: RFC 2327
 SDP_T      B00D        String Active Session Time
                                Ref.: RFC 2327
 SDP_R      B00E        String Zero or more repeat times
                                Reference: RFC 2327
 SDP_M      B00F        String Media type, port, transport and format
                                Ref.: RFC 2327

C.12 H.245

 PropertyID Property   Type     Value
            tag
 OLC        C001       Octet    The value of H.245
                                 OpenLogicalChannel structure.
                       string   Ref.: ITU-T H.245
 OLCack     C002       Octet    The value of H.245
                       string   OpenLogicalChannelAck structure.
                                 Ref.: ITU-T H.245
 OLCcnf     C003       Octet    The value of H.245
                       string   OpenLogicalChannelConfirm structure.
                                 Ref.: ITU-T H.245
 OLCrej     C004       Octet    The value of H.245
                       string   OpenLogicalChannelReject structure.
                                 Ref.: ITU-T H.245
 CLC        C005       Octet    The value of H.245
                       string   CloseLogicalChannel structure.
                                 Ref.: ITU-T H.245
 CLCack     C006       Octet    The value of H.245
                       string   CloseLogicalChannelAck structure.
                                 Ref.: ITU-T H.245

Groves, et al. Standards Track [Page 149] RFC 3525 Gateway Control Protocol June 2003

ANNEX D - Transport over IP

D.1 Transport over IP/UDP using Application Level Framing (ALF)

 Protocol messages defined in this RFC may be transmitted over UDP.
 When no port is provided by the peer (see 7.2.8), commands should be
 sent to the default port number: 2944 for text-encoded operation, or
 2945 for binary-encoded operation.  Responses must be sent to the
 address and port from which the corresponding commands were sent.
 ALF is a set of techniques that allows an application, as opposed to
 a stack, to affect how messages are sent to the other side.  A
 typical ALF technique is to allow an application to change the order
 of messages sent when there is a queue after it has queued them.
 There is no formal specification for ALF.  The procedures in Annex
 D.1 contain a minimum suggested set of ALF behaviours
 Implementors using IP/UDP with ALF should be aware of the
 restrictions of the MTU on the maximum message size.

D.1.1 Providing At-Most-Once functionality

 Messages, being carried over UDP, may be subject to losses.  In the
 absence of a timely response, commands are repeated.  Most commands
 are not idempotent.  The state of the MG would become unpredictable
 if, for example, Add commands were executed several times.  The
 transmission procedures shall thus provide an "At-Most-Once"
 functionality.
 Peer protocol entities are expected to keep in memory a list of the
 responses that they sent to recent transactions and a list of the
 transactions that are currently outstanding.  The transaction
 identifier of each incoming message is compared to the transaction
 identifiers of the recent responses sent to the same MId.  If a match
 is found, the entity does not execute the transaction, but simply
 repeats the response.  If no match is found, the message will be
 compared to the list of currently outstanding transactions.  If a
 match is found in that list, indicating a duplicate transaction, the
 entity does not execute the transaction (see D.1.4 for procedures on
 sending TransactionPending).
 The procedure uses a long timer value, noted LONG-TIMER in the
 following.  The timer should be set larger than the maximum duration
 of a transaction, which should take into account the maximum number

Groves, et al. Standards Track [Page 150] RFC 3525 Gateway Control Protocol June 2003

 of repetitions, the maximum value of the repetition timer and the
 maximum propagation delay of a packet in the network.  A suggested
 value is 30 seconds.
 The copy of the responses may be destroyed either LONG-TIMER seconds
 after the response is issued, or when the entity receives a
 confirmation that the response has been received, through the
 "Response Acknowledgement parameter".  For transactions that are
 acknowledged through this parameter, the entity shall keep a copy of
 the transaction-id for LONG-TIMER seconds after the response is
 issued, in order to detect and ignore duplicate copies of the
 transaction request that could be produced by the network.

D.1.2 Transaction identifiers and three-way handshake

D.1.2.1 Transaction identifiers

 Transaction identifiers are 32-bit integer numbers.  A Media Gateway
 Controller may decide to use a specific number space for each of the
 MGs that they manage, or to use the same number space for all MGs
 that belong to some arbitrary group.  MGCs may decide to share the
 load of managing a large MG between several independent processes.
 These processes will share the same transaction number space.  There
 are multiple possible implementations of this sharing, such as having
 a centralized allocation of transaction identifiers, or
 pre-allocating non-overlapping ranges of identifiers to different
 processes.  The implementations shall guarantee that unique
 transaction identifiers are allocated to all transactions that
 originate from a logical MGC (identical mId).  MGs can simply detect
 duplicate transactions by looking at the transaction identifier and
 mId only.

D.1.2.2 Three-way handshake

 The TransactionResponse Acknowledgement parameter can be found in any
 message.  It carries a set of "confirmed transaction-id ranges".
 Entities may choose to delete the copies of the responses to
 transactions whose id is included in "confirmed transaction-id
 ranges" received in the transaction response messages.  They should
 silently discard further commands when the transaction-id falls
 within these ranges.
 The "confirmed transaction-id ranges" values shall not be used if
 more than LONG-TIMER seconds have elapsed since the MG issued its
 last response to that MGC, or when a MG resumes operation.  In this
 situation, transactions should be accepted and processed, without any
 test on the transaction-id.

Groves, et al. Standards Track [Page 151] RFC 3525 Gateway Control Protocol June 2003

 Messages that carry the "Transaction Response Acknowledgement"
 parameter may be transmitted in any order.  The entity shall retain
 the "confirmed transaction-id ranges" received for LONG-TIMER
 seconds.
 In the binary encoding, if only the firstAck is present in a response
 acknowledgement (see A.2), only one transaction is acknowledged.  If
 both firstAck and lastAck are present, then the range of transactions
 from firstAck to lastAck is acknowledged.  In the text encoding, a
 horizontal dash is used to indicate a range of transactions being
 acknowledged (see B.2).

D.1.3 Computing retransmission timers

 It is the responsibility of the requesting entity to provide suitable
 timeouts for all outstanding transactions, and to retry transactions
 when timeouts have been exceeded.  Furthermore, when repeated
 transactions fail to be acknowledged, it is the responsibility of the
 requesting entity to seek redundant services and/or clear existing or
 pending connections.
 The specification purposely avoids specifying any value for the
 retransmission timers.  These values are typically network dependent.
 The retransmission timers should normally estimate the timer value by
 measuring the time spent between the sending of a command and the
 return of a response.  Implementations SHALL ensure that the
 algorithm used to calculate retransmission timing performs an
 exponentially increasing backoff of the retransmission timeout for
 each retransmission or repetition after the first one.
   NOTE - One possibility is to use the algorithm implemented in
   TCP-IP, which uses two variables:
  1. The average acknowledgement delay (AAD), estimated through an

exponentially smoothed average of the observed delays.

  1. The average deviation (ADEV), estimated through an exponentially

smoothed average of the absolute value of the difference between

    the observed delay and the current average.  The retransmission
    timer, in TCP, is set to the sum of the average delay plus N times
    the average deviation.  The maximum value of the timer should
    however be bounded for the protocol defined in this
    RFC, in order to guarantee that no repeated packet
    would be received by the gateways after LONG-TIMER seconds.  A
    suggested maximum value is 4 seconds.

Groves, et al. Standards Track [Page 152] RFC 3525 Gateway Control Protocol June 2003

 After any retransmission, the entity SHOULD do the following:
  1. It should double the estimated value of the average delay, AAD.
  1. It should compute a random value, uniformly distributed between

0.5 AAD and AAD.

  1. It should set the retransmission timer to the sum of that random

value and N times the average deviation.

 This procedure has two effects.  Because it includes an exponentially
 increasing component, it will automatically slow down the stream of
 messages in case of congestion.  Because it includes a random
 component, it will break the potential synchronization between
 notifications triggered by the same external event.

D.1.4 Provisional responses

 Executing some transactions may require a long time.  Long execution
 times may interact with the timer-based retransmission procedure.
 This may result either in an inordinate number of retransmissions, or
 in timer values that become too long to be efficient.  Entities that
 can predict that a transaction will require a long execution time may
 send a provisional response, "Transaction Pending".  They SHOULD send
 this response if they receive a repetition of a transaction that is
 still being executed.
 Entities that receive a Transaction Pending shall switch to a
 different repetition timer for repeating requests.  The root
 Termination has a property (ProvisionalResponseTimerValue), which can
 be set to the requested maximum number of milliseconds between
 receipt of a command and transmission of the TransactionPending
 response.  Upon receipt of a final response following receipt of
 provisional responses, an immediate confirmation shall be sent, and
 normal repetition timers shall be used thereafter.  An entity that
 sends a provisional response, SHALL include the immAckRequired field
 in the ensuing final response, indicating that an immediate
 confirmation is expected.  Receipt of a Transaction Pending after
 receipt of a reply shall be ignored.

D.1.5 Repeating Requests, Responses and Acknowledgements

 The protocol is organized as a set of transactions, each of which is
 composed of a request and a response, commonly referred to as an
 acknowledgement.  The protocol messages, being carried over UDP, may
 be subject to losses.  In the absence of a timely response,
 transactions are repeated.  Entities are expected to keep in memory a

Groves, et al. Standards Track [Page 153] RFC 3525 Gateway Control Protocol June 2003

 list of the responses that they sent to recent transactions, i.e., a
 list of all the responses they sent over the last LONG-TIMER seconds,
 and a list of the transactions that are currently being executed.
 The repetition mechanism is used to guard against three types of
 possible errors:
  1. transmission errors, when for example a packet is lost due to

noise on a line or congestion in a queue;

  1. component failure, when for example an interface to a entity

becomes unavailable;

  1. entity failure, when for example an entire entity becomes

unavailable.

 The entities should be able to derive from the past history an
 estimate of the packet loss rate due to transmission errors.  In a
 properly configured system, this loss rate should be kept very low,
 typically less than 1%.  If a Media Gateway Controller or a Media
 Gateway has to repeat a message more than a few times, it is very
 legitimate to assume that something else than a transmission error is
 occurring.   For example, given a loss rate of 1%, the probability
 that five consecutive transmission attempts fail is 1 in 100 billion,
 an event that should occur less than once every 10 days for a Media
 Gateway Controller that processes 1000 transactions per second.
 (Indeed, the number of repetition that is considered excessive should
 be a function of the prevailing packet loss rate.)  We should note
 that the "suspicion threshold", which we will call "Max1", is
 normally lower than the "disconnection threshold", which should be
 set to a larger value.
 A classic retransmission algorithm would simply count the number of
 successive repetitions, and conclude that the association is broken
 after retransmitting the packet an excessive number of times
 (typically between 7 and 11 times.)  In order to account for the
 possibility of an undetected or in  progress "failover", we modify
 the classic algorithm so that if the Media Gateway receives a valid
 ServiceChange message announcing a failover, it will start
 transmitting outstanding commands to that new MGC.  Responses to
 commands are still transmitted to the source address of the command.
 In order to automatically adapt to network load, this RFC specifies
 exponentially increasing timers.  If the initial timer is set to 200
 milliseconds, the loss of a fifth retransmission will be detected
 after about 6 seconds.  This is probably an acceptable waiting delay
 to detect a failover.  The repetitions should continue after that
 delay not only in order to perhaps overcome a transient connectivity

Groves, et al. Standards Track [Page 154] RFC 3525 Gateway Control Protocol June 2003

 problem, but also in order to allow some more time for the execution
 of a failover  (waiting a total delay of 30 seconds is probably
 acceptable).
 It is, however, important that the maximum delay of retransmissions
 be bounded.  Prior to any retransmission, it is checked that the time
 elapsed since the sending of the initial datagram is no greater than
 T-MAX.  If more than T-MAX time has elapsed, the MG concludes that
 the MGC has failed, and it begins its recovery process as described
 in section 11.5.  If the MG retries to connect to the current MGC it
 shall use a ServiceChange with ServiceChangeMethod set to
 Disconnected so that the new MGC will be aware that the MG lost one
 or more transactions.  The value T-MAX is related to the LONG-TIMER
 value: the LONG-TIMER value is obtained by adding to T  MAX the
 maximum propagation delay in the network.

D.2 Using TCP

 Protocol messages as defined in this RFC may be transmitted over TCP.
 When no port is specified by the other side (see 7.2.8), the commands
 should be sent to the default port.  The defined protocol has
 messages as the unit of transfer, while TCP is a stream-oriented
 protocol.  TPKT, according to RFC 1006, SHALL be used to delineate
 messages within the TCP stream.
 In a transaction-oriented protocol, there are still ways for
 transaction requests or responses to be lost.  As such, it is
 recommended that entities using TCP transport implement application
 level timers for each request and each response, similar to those
 specified for application level framing over UDP.

D.2.1 Providing the At-Most-Once functionality

 Messages, being carried over TCP, are not subject to transport
 losses, but loss of a transaction request or its reply may
 nonetheless be noted in real implementations.  In the absence of a
 timely response, commands are repeated.  Most commands are not
 idempotent.  The state of the MG would become unpredictable if, for
 example, Add commands were executed several times.
 To guard against such losses, it is recommended that entities follow
 the procedures in D.1.1.

D.2.2 Transaction identifiers and three-way handshake

 For the same reasons, it is possible that transaction replies may be
 lost even with a reliable delivery protocol such as TCP.  It is
 recommended that entities follow the procedures in D.1.2.2.

Groves, et al. Standards Track [Page 155] RFC 3525 Gateway Control Protocol June 2003

D.2.3 Computing retransmission timers

 With reliable delivery, the incidence of loss of a transaction
 request or reply is expected to be very low.  Therefore, only simple
 timer mechanisms are required.  Exponential back-off algorithms
 should not be necessary, although they could be employed where, as in
 an MGC, the code to do so is already required, since MGCs must
 implement ALF/UDP as well as TCP.

D.2.4 Provisional responses

 As with UDP, executing some transactions may require a long time.
 Entities that can predict that a transaction will require a long
 execution time may send a provisional response, "Transaction
 Pending".  They should send this response if they receive a
 repetition of a transaction that is still being executed.
 Entities that receive a Transaction Pending shall switch to a longer
 repetition timer for that transaction.
 Entities shall retain Transactions and replies until they are
 confirmed.  The basic procedure of D.1.4 should be followed, but
 simple timer values should be sufficient.  There is no need to send
 an immediate confirmation upon receipt of a final response.

D.2.5 Ordering of commands

 TCP provides ordered delivery of transactions.  No special procedures
 are required.  It should be noted that ALF/UDP allows sending entity
 to modify its behaviour under congestion, and in particular, could
 reorder transactions when congestion is encountered.  TCP could not
 achieve the same results.

Groves, et al. Standards Track [Page 156] RFC 3525 Gateway Control Protocol June 2003

ANNEX E - Basic packages

 This annex contains definitions of some packages for use with
 Recommendation H.248.1.

E.1 Generic

 PackageID: g (0x0001)
 Version: 1
 Extends: None
 Description:
    Generic package for commonly encountered items.

E.1.1 Properties

 None.

E.1.2 Events

 Cause
    EventID: cause (0x0001)
    Generic error event
    EventsDescriptor parameters:  None
    ObservedEvents Descriptor Parameters:
       General Cause
       ParameterID: Generalcause (0x0001)
          This parameter groups the failures into six groups, which
          the MGC may act upon.
          Type: enumeration
          Possible values:
                   "NR" Normal Release (0x0001)
                   "UR" Unavailable Resources (0x0002)
                   "FT" Failure, Temporary (0x0003)
                   "FP" Failure, Permanent (0x0004)
                   "IW" Interworking Error (0x0005)
                   "UN" Unsupported (0x0006)
       Failure Cause
       ParameterID: Failurecause (0x0002)

Groves, et al. Standards Track [Page 157] RFC 3525 Gateway Control Protocol June 2003

          Possible values:  OCTET STRING
          Description: The Failure Cause is the value generated by the
          Released equipment, i.e., a released network connection.
          The concerned value is defined in the appropriate bearer
          control protocol.
 Signal Completion
    EventID: sc (0x0002)
    Indicates the termination of a signal for which the
    notifyCompletion parameter was set to enable reporting of a
    completion event.  For further procedural description, see 7.1.1,
    7.1.17 and 7.2.7.
    EventsDescriptor parameters:  None
    ObservedEvents Descriptor parameters:
       Signal Identity
       ParameterID: SigID (0x0001)
          This parameter identifies the signal which has terminated.
          For a signal that is contained in a signal list, the signal
          list identity parameter should also be returned indicating
          the appropriate list.
          Type: Binary: octet (string), Text: string
          Possible values: a signal which has terminated.  A signal
          shall be identified using the pkgdName syntax without
          wildcarding.
       Termination Method
       ParameterID: Meth (0x0002)
          Indicates the means by which the signal terminated.
          Type: enumeration
          Possible values:
             "TO" (0x0001) Signal timed out or otherwise completed on
             its own
             "EV" (0x0002) Interrupted by event
             "SD" (0x0003) Halted by new Signals descriptor
             "NC" (0x0004) Not completed, other cause

Groves, et al. Standards Track [Page 158] RFC 3525 Gateway Control Protocol June 2003

       Signal List ID
       ParameterID:  SLID (0x0003)
          Indicates to which signal list a signal belongs.  The
          SignalList ID is only returned in cases where the signal
          resides in a signal list.
          Type: integer
          Possible values: any integer

E.1.3 Signals

 None.

E.1.4 Statistics

 None.

E.2 Base Root Package

 PackageID: root (0x0002)
 Version: 1
 Extends: None
 Description:
    This package defines Gateway wide properties.

E.2.1 Properties

 MaxNrOfContexts
 PropertyID: maxNumberOfContexts (0x0001)
    The value of this property gives the maximum number of contexts
    that can exist at any time.  The NULL context is not included in
    this number.
    Type: double
    Possible values: 1 and up
    Defined in: TerminationState
    Characteristics: read only
 MaxTerminationsPerContext
 PropertyID: maxTerminationsPerContext (0x0002)

Groves, et al. Standards Track [Page 159] RFC 3525 Gateway Control Protocol June 2003

    The maximum number of allowed terminations in a context, see 6.1
    Type: integer
    Possible values: any integer
    Defined in: TerminationState
    Characteristics: read only
 normalMGExecutionTime
 PropertyId: normalMGExecutionTime (0x0003)
    Settable by the MGC to indicate the interval within which the MGC
    expects a response to any transaction from the MG (exclusive of
    network delay)
    Type: integer
    Possible values: any integer, represents milliseconds
    Defined in: TerminationState
    Characteristics: read / write
 normalMGCExecutionTime
 PropertyId: normalMGCExecutionTime (0x0004)
    Settable by the MGC to indicate the interval within which the MG
    should expects a response to any transaction from the MGC
    (exclusive of network delay)
    Type: integer
    Possible values: any integer, represents milliseconds
    Defined in: TerminationState
    Characteristics: read / write
 MGProvisionalResponseTimerValue
 PropertyId: MGProvisionalResponseTimerValue (0x0005)
    Indicates the time within which the MGC should expect a Pending
    Response from the MG if a Transaction cannot be completed.
    Initially set to normalMGExecutionTime plus network delay, but may
    be lowered.

Groves, et al. Standards Track [Page 160] RFC 3525 Gateway Control Protocol June 2003

    Type: Integer
    Possible Values: any integer, represents milliseconds
    Defined in: TerminationState
    Characteristics: read / write
 MGCProvisionalResponseTimerValue
 PropertyId: MGCProvisionalResponseTimerValue (0x0006)
    Indicates the time within which the MG should expect a Pending
    Response from the MGC if a Transaction cannot be completed.
    Initially set to normalMGCExecutionTime plus network delay, but
    may be lowered.
    Type: Integer
    Possible Values: any integer, represents milliseconds
    Defined in: TerminationState
    Characteristics: read / write

E.2.2 Events

 None.

E.2.3 Signals

 None.

E.2.4 Statistics

 None.

E.2.5 Procedures

 None.

E.3 Tone Generator Package

 PackageID: tonegen (0x0003)
 Version: 1
 Extends: None

Groves, et al. Standards Track [Page 161] RFC 3525 Gateway Control Protocol June 2003

 Description:
    This package defines signals to generate audio tones.  This
    package does not specify parameter values.  It is intended to be
    extendable.  Generally, tones are defined as an individual signal
    with a parameter, ind, representing "interdigit" time delay, and a
    tone id to be used with playtones.  A tone id should be kept
    consistent with any tone generation for the same tone.  MGs are
    expected to be provisioned with the characteristics of appropriate
    tones for the country in which the MG is located.
 Designed to be extended only.

E.3.1 Properties

 None.

E.3.2 Events

 None.

E.3.3 Signals

 Play tone
 SignalID: pt (0x0001)
    Plays audio tone over an audio channel
    Signal Type: Brief
    Duration: Provisioned
    Additional parameters:
       Tone id list
       ParameterID: tl (0x0001)
          Type: list of tone ids
          List of tones to be played in sequence.  The list SHALL
          contain one or more tone ids.
       Inter signal duration
       ParameterID: ind (0x0002)
          Type: integer
          Timeout between two consecutive tones in milliseconds

Groves, et al. Standards Track [Page 162] RFC 3525 Gateway Control Protocol June 2003

 No tone ids are specified in this package.  Packages that extend this
 package can add possible values for tone id as well as adding
 individual tone signals.

E.3.4 Statistics

 None.

E.3.5 Procedures

 None.

E.4 Tone Detection Package

 PackageID: tonedet (0x0004)
 Version: 1
 Extends: None
 This Package defines events for audio tone detection.  Tones are
 selected by name (tone id).  MGs are expected to be provisioned with
 the characteristics of appropriate tones for the country in which the
 MG is located.
 Designed to be extended only:
    This package does not specify parameter values.  It is intended to
    be extendable.

E.4.1 Properties

 None.

E.4.2 Events

 Start tone detected
 EventID: std, 0x0001
    Detects the start of a tone.  The characteristics of positive tone
    detection are implementation dependent.
    EventsDescriptor parameters:
       Tone id list
       ParameterID: tl (0x0001)
          Type: list of tone ids

Groves, et al. Standards Track [Page 163] RFC 3525 Gateway Control Protocol June 2003

          Possible values: The only tone id defined in this package is
          "wild card" which is "*" in text encoding and 0x0000 in
          binary.  Extensions to this package would add possible
          values for tone id.  If tl is "wild card", any tone id is
          detected.
       ObservedEventsDescriptor parameters:
       Tone id
       ParameterID: tid (0x0003)
          Type: enumeration
          Possible values: "wildcard" as defined above is the only
          value defined in this package.  Extensions to this package
          would add additional possible values for tone id.
       End tone detected
       EventID: etd, 0x0002
       Detects the end of a tone.
       EventDescriptor parameters:
          Tone id list
          ParameterID: tl (0x0001)
             Type: enumeration or list of enumerated types
             Possible values: No possible values are specified in this
             package.  Extensions to this package would add possible
             values for tone id.
       ObservedEventsDescriptor parameters:
          Tone id
          ParameterID: tid (0x0003)
             Type: enumeration
             Possible values: "wildcard" as defined above is the only
             value defined in this package.  Extensions to this
             package would add possible values for tone id.
          Duration
          ParameterId: dur (0x0002)
             Type: integer, in milliseconds

Groves, et al. Standards Track [Page 164] RFC 3525 Gateway Control Protocol June 2003

             This parameter contains the duration of the tone from
             first detection until it stopped.
 Long tone detected
 EventID: ltd, 0x0003
    Detects that a tone has been playing for at least a certain amount
    of time.
    EventDescriptor parameters:
       Tone id list
       ParameterID: tl (0x0001)
          Type: enumeration or list
          Possible values: "wildcard" as defined above is the only
          value defined in this package.  Extensions to this package
          would add possible values for tone id.
       Duration
       ParameterID: dur (0x0002)
          Type: integer, duration to test against
          Possible values: any legal integer, expressed in
          milliseconds
    ObservedEventsDescriptor parameters:
       Tone id
       ParameterID: tid (0x0003)
          Type: Enumeration
          Possible values: No possible values are specified in this
          package.  Extensions to this package would add possible
          values for tone id.

E.4.3 Signals

 None.

E.4.4 Statistics

 None.

Groves, et al. Standards Track [Page 165] RFC 3525 Gateway Control Protocol June 2003

E.4.5 Procedures

 None.

E.5 Basic DTMF Generator Package

 PackageID: dg (0x0005)
 Version: 1
 Extends: tonegen version 1
 This package defines the basic DTMF tones as signals and extends the
 allowed values of parameter tl of playtone in tonegen.

E.5.1 Properties

 None.

E.5.2 Events

 None.

E.5.3 Signals

 DTMF character 0
 SignalID: d0 (0x0010)
    Generate DTMF 0 tone.  The physical characteristic of DTMF 0 is
    defined in the gateway.
    Signal Type: Brief
    Duration: Provisioned
    Additional parameters:
       None.
 Additional values:
    d0 (0x0010) is defined as a tone id for playtone
 The other DTMF characters are specified in exactly the same way.  A
 table with all signal names and signal IDs is included.  Note that
 each DTMF character is defined as both a signal and a tone id, thus
 extending the basic tone generation package.  Also note that DTMF
 SignalIds are different from the names used in a digit map.

Groves, et al. Standards Track [Page 166] RFC 3525 Gateway Control Protocol June 2003

                   Signal name     Signal ID/Tone id
                  DTMF character 0    d0 (0x0010)
                  DTMF character 1    d1 (0x0011)
                  DTMF character 2    d2 (0x0012)
                  DTMF character 3    d3 (0x0013)
                  DTMF character 4    d4 (0x0014)
                  DTMF character 5    d5 (0x0015)
                  DTMF character 6    d6 (0x0016)
                  DTMF character 7    d7 (0x0017)
                  DTMF character 8    d8 (0x0018)
                  DTMF character 9    d9 (0x0019)
                  DTMF character *    ds (0x0020)
                  DTMF character #    do (0x0021)
                  DTMF character A    da (0x001a)
                  DTMF character B    db (0x001b)
                  DTMF character C    dc (0x001c)
                  DTMF character D    dd (0x001d)

E.5.4 Statistics

 None.

E.5.5 Procedures

 None.

E.6 DTMF detection Package

 PackageID: dd (0x0006)
 Version: 1
 Extends: tonedet version 1
 This package defines the basic DTMF tones detection.  This Package
 extends the possible values of tone id in the "start tone detected"
 "end tone detected" and "long tone detected" events.
 Additional tone id values are all tone ids described in package dg
 (basic DTMF generator package).
 The following table maps DTMF events to digit map symbols as
 described in 7.1.14.
                         DTMF Event Symbol
                         d0   "0"
                         d1   "1"
                         d2   "2"

Groves, et al. Standards Track [Page 167] RFC 3525 Gateway Control Protocol June 2003

                         d3   "3"
                         d4   "4"
                         d5   "5"
                         d6   "6"
                         d7   "7"
                         d8   "8"
                         d9   "9"
                         da   "A" or "a"
                         db   "B" or "b"
                         dc   "C" or "c"
                         dd   "D" or "d"
                         ds   "E" or "e"
                         do   "F" or "f"

E.6.1 Properties

 None.

E.6.2 Events

 DTMF digits
    EventIds are defined with the same names as the SignalIds defined
    in the table found in E.5.3.
 DigitMap Completion Event
 EventID: ce, 0x0004
    Generated when a digit map completes as described in 7.1.14.
    EventsDescriptor parameters: None.
    ObservedEventsDescriptor parameters:
       DigitString
       ParameterID: ds (0x0001)
          Type: string of digit map symbols (possibly empty) returned
          as a quotedString
          Possible values: a sequence of the characters "0" through
          "9", "A" through "F", and the long duration modifier "Z".
          Description: the portion of the current dial string as
          described in 7.1.14 which matched part or all of an
          alternative event sequence specified in the digit map.

Groves, et al. Standards Track [Page 168] RFC 3525 Gateway Control Protocol June 2003

       Termination Method
       ParameterID: Meth (0x0003)
          Type: enumeration
          Possible values:
             "UM" (0x0001) Unambiguous match
             "PM" (0x0002) Partial match, completion by timer expiry
             or unmatched event
             "FM" (0x0003) Full match, completion by timer expiry or
             unmatched event
          Description: indicates the reason for generation of the
          event.  See the procedures in 7.1.14.

E.6.3 Signals

 None.

E.6.4 Statistics

 None.

E.6.5 Procedures

 Digit map processing is activated only if an events descriptor is
 activated that contains a digit map completion event as defined in
 Section E.6.2 and that digit map completion event contains an eventDM
 field in the requested actions as defined in Section 7.1.9.  Other
 parameters such as KeepActive or embedded events of signals
 descriptors may also be present in the events descriptor and do not
 affect the activation of digit map processing.

E.7 Call Progress Tones Generator Package

 PackageID: cg, 0x0007
 Version: 1
 Extends: tonegen version 1
 This package defines the basic call progress tones as signals and
 extends the allowed values of the tl parameter of playtone in
 tonegen.

Groves, et al. Standards Track [Page 169] RFC 3525 Gateway Control Protocol June 2003

E.7.1 Properties

 None.

E.7.2 Events

 None.

E.7.3 Signals

 Dial Tone
 SignalID: dt (0x0030)
    Generate dial tone.  The physical characteristic of dial tone is
    available in the gateway.
    Signal Type: TimeOut
    Duration: Provisioned
    Additional parameters:
       None.
 Additional values:
    dt (0x0030) is defined as a tone id for playtone
 The other tones of this package are defined in exactly the same way.
 A table with all signal names and signal IDs is included.  Note that
 each tone is defined as both a signal and a tone id, thus extending
 the basic tone generation package.
   Signal Name                 Signal ID/tone id
   Dial Tone                   dt (0x0030)
   Ringing Tone                rt (0x0031)
   Busy Tone                   bt (0x0032)
   Congestion Tone             ct (0x0033)
   Special Information Tone    sit(0x0034)
   Warning Tone                wt (0x0035)
   Payphone Recognition Tone   prt (0x0036)
   Call Waiting Tone           cw (0x0037)
   Caller Waiting Tone         cr (0x0038)

E.7.4 Statistics

 None.

Groves, et al. Standards Track [Page 170] RFC 3525 Gateway Control Protocol June 2003

E.7.5 Procedures

    NOTE - The required set of tone ids corresponds to those defined
    in Recommendation E.180/Q.35.  See Recommendation E.180/Q.35 for
    definition of the meanings of these tones.

E.8 Call Progress Tones Detection Package

 PackageID: cd (0x0008)
 Version: 1
 Extends: tonedet version 1
 This package defines the basic call progress detection tones.  This
 package extends the possible values of tone id in the "start tone
 detected", "end tone detected" and "long tone detected" events.
 Additional values
    toneID values are defined for start tone detected, end tone
    detected and long tone detected with the same values as those in
    package cg (call progress tones generation package).
 The required set of tone ids corresponds to Recommendation
 E.180/Q.35.  See Recommendation E.180/Q.35 for definition of the
 meanings of these tones.

E.8.1 Properties

 None.

E.8.2 Events

 Events are defined as in the call progress tones generator package
 (cg) for the tones listed in the table of E.7.3.

E.8.3 Signals

 None.

E.8.4 Statistics

 None.

E.8.5 Procedures

 None.

Groves, et al. Standards Track [Page 171] RFC 3525 Gateway Control Protocol June 2003

E.9 Analog Line Supervision Package

 PackageID: al, 0x0009
 Version: 1
 Extends: None
 This package defines events and signals for an analog line.
 E.9.1 Properties
 None.

E.9.2 Events

 onhook
 EventID: on (0x0004)
    Detects handset going on hook.  Whenever an events descriptor is
    activated that requests monitoring for an on-hook event and the
    line is already on-hook, then the MG shall behave according to the
    setting of the "strict" parameter.
    EventDescriptor parameters:
       Strict Transition
       ParameterID: strict (0x0001)
          Type: enumeration
          Possible values: "exact" (0x00), "state" (0x01), "failWrong"
          (0x02)
            "exact" means that only an actual hook state transition to
            on-hook is to be recognized;
            "state" means that the event is to be recognized either if
            the hook state transition is detected or if the hook state
            is already on-hook;
            "failWrong" means that if the hook state is already
            on-hook, the command fails and an error is reported.
    ObservedEventsDescriptor parameters:
       Initial State
       ParameterID: init (0x0002)
          Type: Boolean

Groves, et al. Standards Track [Page 172] RFC 3525 Gateway Control Protocol June 2003

          Possible values:
             "True" means that the event was reported because the line
             was already on-hook when the events descriptor containing
             this event was activated;
             "False" means that the event represents an actual state
             transition to on-hook.
 offhook
 EventID: of (0x0005)
    Detects handset going off hook.  Whenever an events descriptor is
    activated that requests monitoring for an off-hook event and the
    line is already off-hook, then the MG shall behave according to
    the setting of the "strict" parameter.
    EventDescriptor parameters:
       Strict Transition
       ParameterID: strict (0x0001)
          Type: enumeration
          Possible values: "exact" (0x00), "state" (0x01), "failWrong"
          (0x02)
             "exact" means that only an actual hook state transition
             to off-hook is to be recognized;
             "state" means that the event is to be recognized either
             if the hook state transition is detected or if the hook
             state is already off-hook;
             "failWrong" means that if the hook state is already off-
             hook, the command fails and an error is reported.
    ObservedEventsDescriptor parameters
       Initial State
       ParameterID: init (0x0002)
          Type: Boolean

Groves, et al. Standards Track [Page 173] RFC 3525 Gateway Control Protocol June 2003

          Possible values:
             "True" means that the event was reported because the line
             was already off-hook when the events descriptor
             containing this event was activated;
             "False" means that the event represents an actual state
             transition to off-hook.
 flashhook
 EventID: fl, 0x0006
    Detects handset flash.  A flash occurs when an onhook is followed
    by an offhook between a minimum and maximum duration.
    EventDescriptor parameters:
       Minimum duration
       ParameterID: mindur (0x0004)
          Type: integer in milliseconds
          Default value is provisioned.
       Maximum duration
       ParameterID: maxdur (0x0005)
          Type: integer in milliseconds
          Default value is provisioned.
    ObservedEventsDescriptor parameters:
       None

E.9.3 Signals

 ring
 SignalID: ri, 0x0002
    Applies ringing on the line
    Signal Type: TimeOut
    Duration: Provisioned

Groves, et al. Standards Track [Page 174] RFC 3525 Gateway Control Protocol June 2003

    Additional parameters:
       Cadence
       ParameterID: cad (0x0006)
          Type: list of integers representing durations of alternating
          on and off segments, constituting a complete ringing cycle
          starting with an on.  Units in milliseconds
          Default is fixed or provisioned.  Restricted function MGs
          may ignore cadence values they are incapable of generating.
       Frequency
       ParameterID: freq (0x0007)
          Type: integer in Hz
          Default is fixed or provisioned.  Restricted function MGs
          may ignore frequency values they are incapable of
          generating.

E.9.4 Statistics

 None.

E.9.5 Procedures

 If the MGC sets an EventsDescriptor containing a hook state
 transition event (on-hook or off-hook) with the "strict" (0x0001)
 parameter set to "failWrong", and the hook state is already what the
 transition implies, the execution of the command containing that
 EventsDescriptor fails.  The MG SHALL include error code 540
 "Unexpected initial hook state" in its reponse.

E.9.6 Error code

 This package defines a new error code:
    540 - Unexpected initial hook state
 The procedure for use of this code is given in E.9.5.

E.10 Basic Continuity Package

 PackageID: ct (0x000a)
 Version: 1
 Extends: None

Groves, et al. Standards Track [Page 175] RFC 3525 Gateway Control Protocol June 2003

 This package defines events and signals for continuity test.  The
 continuity test includes provision of either a loopback or
 transceiver functionality.

E.10.1 Properties

 None.

E.10.2 Events

 Completion
 EventID: cmp, 0x0005
    This event detects test completion of continuity test.
    EventDescriptor parameters
       None.
    ObservedEventsDescriptor parameters
       Result
       ParameterID: res (0x0008)
          Type: enumeration
          Possible values: success (0x0001), failure (0x0000)

E.10.3 Signals

 Continuity test
 SignalID: ct (0x0003)
    Initiates sending of continuity test tone on the termination to
    which it is applied.
    Signal Type: TimeOut
    Default value is provisioned
    Additional parameters:
       None.
 Respond
 SignalID: rsp (0x0004)

Groves, et al. Standards Track [Page 176] RFC 3525 Gateway Control Protocol June 2003

    The signal is used to respond to a continuity test.  See E.10.5
    for further explanation.
    Signal Type: On/Off
    Default duration is provisioned
    Additional parameters:
       None.

E.10.4 Statistics

 None.

E.10.5 Procedures

 When a MGC wants to initiate a continuity test, it sends a command to
 the MG containing:
  1. a signals descriptor with the ct signal; and
  1. an events descriptor containing the cmp event.
 Upon reception of a command containing the ct signal and cmp event,
 the MG initiates the continuity test tone for the specified
 Termination.  If the return tone is detected and any other required
 conditions are satisfied before the signal times out, the cmp event
 shall be generated with the value of the result parameter equal to
 success.  In all other cases, the cmp event shall be generated with
 the value of the result parameter equal to failure.
 When a MGC wants the MG to respond to a continuity test, it sends a
 command to the MG containing a signals descriptor with the rsp
 signal.  Upon reception of a command with the rsp signal, the MG
 either applies a loopback or (for 2-wire circuits) awaits reception
 of a continuity test tone.  In the loopback case, any incoming
 information shall be reflected back as outgoing information.  In the
 2-wire case, any time the appropriate test tone is received, the
 appropriate response tone should be sent.  The MGC determines when to
 remove the rsp signal.
 When a continuity test is performed on a Termination, no echo devices
 or codecs shall be active on that Termination.
 Performing voice path assurance as part of continuity testing is
 provisioned by bilateral agreement between network operators.

Groves, et al. Standards Track [Page 177] RFC 3525 Gateway Control Protocol June 2003

    (Informative Note) Example tones and test procedure details are
    given in Q.724 sections 7 and 8, Q.764 section 2.1.8 and Q.1902.4.

E.11 Network Package

 PackageID: nt (0x000b)
 Version: 1
 Extends: None
 This package defines properties of network terminations independent
 of network type.

E.11.1 Properties

 Maximum Jitter Buffer
 PropertyID: jit (0x0007)
    This property puts a maximum size on the jitter buffer.
    Type: integer in milliseconds
    Possible values: This property is specified in milliseconds.
    Defined in: LocalControlDescriptor
    Characteristics: read/write

E.11.2 Events

 network failure
 EventID: netfail, 0x0005
    The termination generates this event upon detection of a failure
    due to external or internal network reasons.
    EventDescriptor parameters
       None.
    ObservedEventsDescriptor parameters
       cause
       ParameterID: cs (0x0001)
          Type: string
          Possible values: any text string

Groves, et al. Standards Track [Page 178] RFC 3525 Gateway Control Protocol June 2003

          This parameter may be included with the failure event to
          provide diagnostic information on the reason of failure.
 quality alert
 EventID: qualert, 0x0006
    This property allows the MG to indicate a loss of quality of the
    network connection.  The MG may do this by measuring packet loss,
    interarrival jitter, propagation delay and then indicating this
    using a percentage of quality loss.
    EventDescriptor parameters
       Threshold
       ParameterId: th (0x0001)
          Type: integer
          Possible values: 0 to 99
          Description: threshold for percent of quality loss measured,
          calculated based on a provisioned method, that could take
          into consideration packet loss, jitter, and delay for
          example.  Event is triggered when calculation exceeds the
          threshold.
    ObservedEventsDescriptor parameters
       Threshold
       ParameterId: th (0x0001)
          Type: integer
          Possible values: 0 to 99
          Description: percent of quality loss measured, calculated
          based on a provisioned method, that could take into
          consideration packet loss, jitter, and delay for example.

E.11.3 Signals

 None.

Groves, et al. Standards Track [Page 179] RFC 3525 Gateway Control Protocol June 2003

E.11.4 Statistics

 Duration
 StatisticsID: dur (0x0001)
    Description: provides duration of time the termination has been in
    the Context.
    Type: double, in milliseconds
 Octets Sent
 StatisticID: os (0x0002)
    Type: double
    Possible values: any 64-bit integer
 Octets Received
 StatisticID: or (0x0003)
    Type: double
    Possible values: any 64-bit integer

E.11.5 Procedures

 None.

E.12 RTP Package

 PackageID: rtp (0x000c)
 Version: 1
 Extends: Network Package version 1
 This package is used to support packet-based multimedia data transfer
 by means of the Real-time Transport Protocol (RTP) [RFC 1889].

E.12.1 Properties

 None.

E.12.2 Events

 Payload Transition
 EventID: pltrans, 0x0001
    This event detects and notifies when there is a transition of the
    RTP payload format from one format to another.

Groves, et al. Standards Track [Page 180] RFC 3525 Gateway Control Protocol June 2003

    EventDescriptor parameters
       None.
    ObservedEventsDescriptor parameters
       ParameterName: rtppayload
       ParameterID: rtppltype, 0x01
       Type: list of enumerated types.
       Possible values: The encoding method shall be specified by
       using one or several valid encoding names, as defined in the
       RTP AV Profile or registered with IANA.

E.12.3 Signals

 None.

E.12.4 Statistics

 Packets Sent
 StatisticID: ps (0x0004)
    Type: double
    Possible values: any 64-bit integer
 Packets Received
 StatisticID: pr (0x0005)
    Type: double
    Possible values: any 64-bit integer
 Packet Loss
 StatisticID: pl (0x0006)
    Describes the current rate of packet loss on an RTP stream, as
    defined in IETF RFC 1889.  Packet loss is expressed as percentage
    value: number of packets lost in the interval between two
    reception reports, divided by the number of packets expected
    during that interval.
    Type: double
    Possible values: a 32-bit whole number and a 32-bit fraction.

Groves, et al. Standards Track [Page 181] RFC 3525 Gateway Control Protocol June 2003

 Jitter
 StatisticID: jit (0x0007)
    Requests the current value of the interarrival jitter on an RTP
    stream as defined in IETF RFC 1889.  Jitter measures the variation
    in interarrival time for RTP data packets.
 Delay
 StatisticID:delay (0x0008)
    Requests the current value of packet propagation delay expressed
    in timestamp units.  Same as average latency.

E.12.5 Procedures

 None.

E.13 TDM Circuit Package

    PackageID: tdmc (0x000d)
    Version: 1
    Extends: Network Package version 1
    This package may be used by any termination that supports gain and
    echo control.  It was originally intended for use on TDM circuits
    but may be more widely used.
    New versions or extensions of this package should take non-TDM use
    into account.

E.13.1 Properties

    Echo Cancellation
    PropertyID: ec (0x0008)
       Type: boolean
       Possible values:
          "on" (when the echo cancellation is requested) and
          "off" (when it is turned off.)
          The default is provisioned.
       Defined in: LocalControlDescriptor

Groves, et al. Standards Track [Page 182] RFC 3525 Gateway Control Protocol June 2003

       Characteristics: read/write
    Gain Control
    PropertyID: gain (0x000a)
       Gain control, or usage of of signal level adaptation and
       noise level reduction is used to adapt the level of the signal.
       However, it is necessary, for example for modem calls, to turn
       off this function.
       Type: integer
       Possible values:
       The gain control parameter may either be specified as
       "automatic" (0xffffffff), or as an explicit number of decibels
       of gain (any other integer value).  The default is provisioned
       in the MG.
    Defined in: LocalControlDescriptor
    Characteristics: read/write

E.13.2 Events

 None.

E.13.3 Signals

 None.

E.13.4 Statistics

 None.

E.13.5 Procedures

 None.

Groves, et al. Standards Track [Page 183] RFC 3525 Gateway Control Protocol June 2003

APPENDIX I EXAMPLE CALL FLOWS (INFORMATIVE)

 All H.248.1 implementors must read the normative part of this RFC
 carefully before implementing from it.  The examples in this appendix
 should not be used as stand-alone explanations of how to create
 protocol messages.
 The examples in this appendix use SDP for encoding of the Local and
 and Remote stream descriptors. SDP is defined in RFC 2327. If there
 is is any discrepancy between the SDP in the examples, and RFC 2327,
 the the RFC should be consulted for correctness. Audio profiles used
 are are those defined in IETF RFC 1890, and others registered with
 IANA.  For example, G.711 A-law is called PCMA in SDP, and is
 assigned profile 0. G.723.1 is called G723 and is profile 4; H.263 is
 called H263 and is profile 34. See also
 http://www.iana.org/assignments/rtp-parameters.

A.1 Residential Gateway to Residential Gateway Call

 This example scenario illustrates the use of the elements of the
 protocol to set up a Residential Gateway to Residential Gateway call
 over an IP-based network.  For simplicity, this example assumes that
 both Residential Gateways involved in the call are controlled by the
 same Media Gateway Controller.

A.1.1 Programming Residential GW Analog Line Terminations for Idle

 Behavior
 The following illustrates the API invocations from the Media Gateway
 Controller and Media Gateways to get the Terminations in this
 scenario programmed for idle behavior.  Both the originating and
 terminating Media Gateways have idle AnalogLine Terminations
 programmed to look for call initiation events (i.e., -offhook) by
 using the Modify Command with the appropriate parameters.  The null
 Context is used to indicate that the Terminations are not yet
 involved in a Context.  The ROOT termination is used to indicate the
 entire MG instead of a termination within the MG.
 In this example, MG1 has the IP address 124.124.124.222, MG2 is
 125.125.125.111, and the MGC is 123.123.123.4. The default Megaco
 port is 55555 for all three.
 1. An MG registers with an MGC using the ServiceChange command:
 MG1 to MGC:
 MEGACO/1 [124.124.124.222] Transaction = 9998 {
     Context = - {

Groves, et al. Standards Track [Page 184] RFC 3525 Gateway Control Protocol June 2003

         ServiceChange = ROOT {Services {
             Method=Restart,
             ServiceChangeAddress=55555, Profile=ResGW/1}
         }
     } }
 2. The MGC sends a reply:
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555 Reply = 9998 {
    Context = - {ServiceChange = ROOT {
      Services {ServiceChangeAddress=55555, Profile=ResGW/1} } } }
 3. The MGC programs a Termination in the NULL context.  The
 terminationId is A4444, the streamId is 1, the requestId in the
 Events descriptor is 2222.  The mId is the identifier of the sender
 of this message, in this case, it is the IP address and port
 [123.123.123.4]:55555.  Mode for this stream is set to SendReceive.
 "al" is the analog line supervision package.  Local and Remote are
 assumed to be provisioned.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 9999 {
     Context = - {
         Modify = A4444 {
             Media { Stream = 1 {
                      LocalControl {
                          Mode = SendReceive,
                          tdmc/gain=2,  ; in dB,
                          tdmc/ec=on
                      },
                  }
             },
             Events = 2222 {al/of(strict=state)}
         }
     } }
 The dialplan script could have been loaded into the MG previously.
 Its function would be to wait for the OffHook, turn on dialtone and
 start collecting DTMF digits.  However in this example, we use the
 digit map, which is put into place after the offhook is detected
 (step 5 below).

Groves, et al. Standards Track [Page 185] RFC 3525 Gateway Control Protocol June 2003

 Note that the embedded EventsDescriptor could have been used to
 combine steps 3 and 4 with steps 8 and 9, eliminating steps 6 and 7.
 4. The MG1 accepts the Modify with this reply:
 MG1 to MGC:
 MEGACO/1 [124.124.124.222]:55555
 Reply = 9999 {
    Context = - {Modify = A4444} }
 5. A similar exchange happens between MG2 and the MGC, resulting in
 an idle Termination called A5555.

A.1.2 Collecting Originator Digits and Initiating Termination

 The following builds upon the previously shown conditions.  It
 illustrates the transactions from the Media Gateway Controller and
 originating Media Gateway (MG1) to get the originating Termination
 (A4444) through the stages of digit collection required to initiate a
 connection to the terminating Media Gateway (MG2).
 6. MG1 detects an offhook event from User 1 and reports it to the
 Media Gateway Controller via the Notify Command.
 MG1 to MGC:
 MEGACO/1 [124.124.124.222]:55555 Transaction = 10000 {
    Context = - {
        Notify = A4444 {ObservedEvents =2222 {
          19990729T22000000:al/of(init=false)}}
    } }
 7. And the Notify is acknowledged.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555 Reply = 10000 {
     Context = - {Notify = A4444} }

Groves, et al. Standards Track [Page 186] RFC 3525 Gateway Control Protocol June 2003

 8. The MGC Modifies the termination to play dial tone, to look for
 digits according to Dialplan0 and to look for the on-hook event now.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 10001 {
     Context = - {
         Modify = A4444 {
             Events = 2223 {
                 al/on(strict=state), dd/ce {DigitMap=Dialplan0}
             },
             Signals {cg/dt},
             DigitMap= Dialplan0{ (0| 00|[1-
 7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)}
         }
     } }
 9. And the Modify is acknowledged.
 MG1 to MGC:
 MEGACO/1 [124.124.124.222]:55555 Reply = 10001 {
     Context = - {Modify = A4444} }
 10.   Next, digits are accumulated by MG1 as they are dialed by User
 1.  Dialtone is stopped upon detection of the first digit.  When an
 appropriate match is made of collected digits against the currently
 programmed Dialplan for A4444, another Notify is sent to the Media
 Gateway Controller.
 MG1 to MGC:
 MEGACO/1 [124.124.124.222]:55555 Transaction = 10002 {
    Context = - {
        Notify = A4444 {ObservedEvents =2223 {
          19990729T22010001:dd/ce{ds="916135551212",Meth=UM}}}
    } }
 11.   And the Notify is acknowledged.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555 Reply = 10002 {
     Context = - {Notify = A4444} }
 12.   The controller then analyses the digits and determines that a
 connection needs to be made from MG1 to MG2.  Both the TDM

Groves, et al. Standards Track [Page 187] RFC 3525 Gateway Control Protocol June 2003

 termination A4444, and an RTP termination are added to a new context
 in MG1.  Mode is ReceiveOnly since Remote descriptor values are not
 yet specified.  Preferred codecs are in the MGC's preferred order of
 choice.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 10003 {
     Context = $ {
        Add = A4444,
        Add = $ {
            Media {
              Stream = 1 {
                   LocalControl {
                       Mode = ReceiveOnly,
                       nt/jit=40 ; in ms
                   },
                   Local { v=0 c=IN IP4 $ m=audio $ RTP/AVP 4
 a=ptime:30 v=0 c=IN IP4 $ m=audio $ RTP/AVP 0
                   }
              }
           }
        }
     } }
    NOTE - The MGC states its preferred parameter values as a series
    of SDP blocks in  Local.  The MG fills in the Local Descriptor in
    the Reply.
 13.   MG1 acknowledges the new Termination and fills in the Local IP
 address and UDP port.  It also makes a choice for the codec based on
 the MGC preferences in Local.  MG1 sets the RTP port to 2222.
 MG1 -> MGC:
 MEGACO/1 [124.124.124.222]:55555 Reply = 10003 {
    Context = 2000 {
       Add = A4444,
       Add=A4445{
          Media {
              Stream = 1 {
                  Local { v=0 o=- 2890844526 2890842807 IN IP4
 124.124.124.222 s=- t= 0 0 c=IN IP4 124.124.124.222 m=audio 2222
 RTP/AVP 4 a=ptime:30 a=recvonly
                  } ; RTP profile for G.723.1 is 4
              }

Groves, et al. Standards Track [Page 188] RFC 3525 Gateway Control Protocol June 2003

          }
       }
    } }
 14.   The MGC will now associate A5555 with a new Context on MG2, and
 establish an RTP Stream (i.e., A5556 will be assigned), SendReceive
 connection through to the originating user, User 1.  The MGC also
 sets ring on A5555.
 MGC to MG2:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 50003 {
     Context = $ {
        Add = A5555  { Media {
             Stream = 1 {
                  LocalControl {Mode = SendReceive} }},
       Events=1234{al/of(strict=state)},
             Signals {al/ri}
             },
        Add  = $ {Media {
             Stream = 1 {
                  LocalControl {
                     Mode = SendReceive,
                     nt/jit=40 ; in ms
                  },
                  Local { v=0 c=IN IP4 $ m=audio $ RTP/AVP 4
 a=ptime:30
                  },
                  Remote { v=0 c=IN IP4 124.124.124.222 m=audio 2222
 RTP/AVP 4 a=ptime:30
                  } ; RTP profile for G.723.1 is 4
              }
           }
       }
    } }
 15.   This is acknowledged.  The stream port number is different from
 the control port number.  In this case it is 1111 (in the SDP).
 MG2 to MGC:
 MEGACO/1 [125.125.125.111]:55555 Reply = 50003 {
    Context = 5000 {
    Add = A5555,
       Add = A5556{
          Media {
             Stream = 1 {

Groves, et al. Standards Track [Page 189] RFC 3525 Gateway Control Protocol June 2003

                 Local { v=0 o=- 7736844526 7736842807 IN IP4
 125.125.125.111 s=- t= 0 0 c=IN IP4 125.125.125.111 m=audio 1111
 RTP/AVP 4 }
             } ; RTP profile for G723.1 is 4
          }
        }
    } }
 16.   The above IPAddr and UDPport need to be given to MG1 now.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 10005 {
   Context = 2000 {
     Modify = A4444 {
       Signals {cg/rt}
     },
     Modify = A4445 {
        Media {
             Stream = 1 {
                 Remote { v=0 o=- 7736844526 7736842807 IN IP4
 125.125.125.111 s=- t= 0 0 c=IN IP4 125.125.125.111 m=audio 1111
 RTP/AVP 4
                 }
             } ; RTP profile for G723.1 is 4
         }
     }
   } }
 MG1 to MGC:
 MEGACO/1 [124.124.124.222]:55555 Reply = 10005 {
    Context = 2000 {Modify = A4444, Modify = A4445} }
 17.   The two gateways are now connected and User 1 hears the
 RingBack.  The MG2 now waits until User2 picks up the receiver and
 then the two-way call is established.

Groves, et al. Standards Track [Page 190] RFC 3525 Gateway Control Protocol June 2003

 From MG2 to MGC:
 MEGACO/1 [125.125.125.111]:55555 Transaction = 50005 {
    Context = 5000 {
        Notify = A5555 {ObservedEvents =1234 {
          19990729T22020002:al/of(init=false)}}
    } }
 From MGC to MG2:
 MEGACO/1 [123.123.123.4]:55555 Reply = 50005 {
     Context = - {Notify = A5555} }
 From MGC to MG2:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 50006 {
    Context = 5000 {
       Modify = A5555 {
          Events = 1235 {al/on(strict=state)},
          Signals { } ; to turn off ringing
       }
    } }
 From MG2 to MGC:
 MEGACO/1 [125.125.125.111]:55555 Reply = 50006 {
  Context = 5000 {Modify = A4445} }
 18.   Change mode on MG1 to SendReceive, and stop the ringback.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 10006 {
    Context = 2000 {
       Modify = A4445 {
          Media {
             Stream = 1 {
                LocalControl {
                   Mode=SendReceive
                }
             }
          }
       },
       Modify = A4444 {
          Signals { }
       }

Groves, et al. Standards Track [Page 191] RFC 3525 Gateway Control Protocol June 2003

    } }
 from MG1 to MGC:
 MEGACO/1 [124.124.124.222]:55555 Reply = 10006 {
    Context = 2000 {Modify = A4445, Modify = A4444}}
 19.   The MGC decides to Audit the RTP termination on MG2.
 MGC -> MG2:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 50007 {
    Context = - {AuditValue = A5556{
       Audit{Media, DigitMap, Events, Signals, Packages, Statistics }}
    } }
 20.   The MG2 replies.
 MG2 -> MGC:
 MEGACO/1 [125.125.125.111]:55555 Reply = 50007 {
    Context = - { AuditValue = A5556 {
           Media {
              TerminationState { ServiceStates = InService,
          Buffer = OFF },
        Stream = 1 {
                  LocalControl { Mode = SendReceive,
                     nt/jit=40 },
                  Local { v=0 o=- 7736844526 7736842807 IN IP4
 125.125.125.111 s=- t= 0 0 c=IN IP4 125.125.125.111 m=audio 1111
 RTP/AVP  4 a=ptime:30
                 },
                  Remote { v=0 o=- 2890844526 2890842807 IN IP4
 124.124.124.222 s=- t= 0 0 c=IN IP4 124.124.124.222 m=audio 2222
 RTP/AVP  4 a=ptime:30
                  } } },
            Events,
         Signals,
         DigitMap,
        Packages {nt-1, rtp-1},
           Statistics { rtp/ps=1200,  ; packets sent
                        nt/os=62300, ; octets sent
                        rtp/pr=700, ; packets received
                        nt/or=45100, ; octets received
                        rtp/pl=0.2,  ; % packet loss
                        rtp/jit=20,
                        rtp/delay=40 } ; avg latency
        }

Groves, et al. Standards Track [Page 192] RFC 3525 Gateway Control Protocol June 2003

     } }
 21.   When the MGC receives an onhook signal from one of the MGs, it
 brings down the call.  In this example, the user at MG2 hangs up
 first.
 From MG2 to MGC:
 MEGACO/1 [125.125.125.111]:55555 Transaction = 50008 {
    Context = 5000 {
        Notify = A5555 {ObservedEvents =1235 {
           19990729T24020002:al/on(init=false)}
        }
    } }
 From MGC to MG2:
 MEGACO/1 [123.123.123.4]:55555 Reply = 50008 {
     Context = - {Notify = A5555} }
 22.   The MGC now sends both MGs a Subtract to take down the call.
 Only the subtracts to MG2 are shown here.  Each termination has its
 own set of statistics that it gathers.  An MGC may not need to
 request both to be returned.  A5555 is a physical termination, and
 A5556 is an RTP termination.
 From MGC to MG2:
 MEGACO/1 [123.123.123.4]:55555 Transaction = 50009 {
    Context = 5000 {
       Subtract = A5555 {Audit{Statistics}},
       Subtract = A5556 {Audit{Statistics}}
    } }
 From MG2 to MGC:
 MEGACO/1 [125.125.125.111]:55555 Reply = 50009 {
    Context = 5000 {
      Subtract = A5555 {
           Statistics {
              nt/os=45123, ; Octets Sent
              nt/dur=40 ; in seconds
              }
        },
        Subtract = A5556 {
           Statistics {
              rtp/ps=1245, ; packets sent

Groves, et al. Standards Track [Page 193] RFC 3525 Gateway Control Protocol June 2003

              nt/os=62345, ; octets sent
              rtp/pr=780, ; packets received
              nt/or=45123, ; octets received
              rtp/pl=10, ;  % packets lost
              rtp/jit=27,
              rtp/delay=48 ; average latency
           }
        }
    } }
 23.   The MGC now sets up both MG1 and MG2 to be ready to detect the
 next off-hook event.  See step 1.  Note that this could be the
 default state of a termination in the null context, and if this were
 the case, no message need be sent from the MGC to the MG.  Once a
 termination returns to the null context, it goes back to the default
 termination values for that termination.

Groves, et al. Standards Track [Page 194] RFC 3525 Gateway Control Protocol June 2003

APPENDIX II Changes From RFC 3015

 In the following table, "source" indicates when the change was first
 approved.  It has the following values:
 IG1100: H.248 Implementor's Guide approved in November, 2000 (as TD
 Plen-39, Christian Groves, editor).
 IG0601: H.248 Implementor's Guide approved in June, 2001 (as  TD
 Plen-15, Christian Groves, editor).
 IGDUB: Draft H.248 Implementor's Guide approved at the Q.3
 Rapporteur's meeting held near Dublin, October 2001 (as TD-28, Terry
 Anderson, editor).
 GEN0202: added at the Geneva meeting, February 2002, which consented
 to H.248 v1 Amendment 1 (as TD Plen-36r1, Marcello Pantaleo, editor).
 ITUPOST: added in post-Geneva editing by the ITU-T.
 TTPOST: added in post-approval editing by the Megaco Chair, Tom
 Taylor, who assembled this document for submission.
 Section    Source                       Change
 1          ITUPOST   Reference changed from H.248 to H.248.1.
 2.1        ITUPOST   Reference added for error codes, changed from
                      H.248 Annex L to H.248.8 (2002).
 2.1        IG1100    Corrected Q.765 reference to Q.765.5.
 2.1        GEN0202   Added reference to X.690.
 2.2        GEN0202   Added reference to H.226.
 2.2         IGDUB    Added informative references to Q.724, Q.764,
                      and Q.1902.4.
 4          IG0601    Added expansion of ALF.
 5          TTPOST    Gave priority to IETF conventions (added at
                      start of document).

Groves, et al. Standards Track [Page 195] RFC 3525 Gateway Control Protocol June 2003

 6.1.1      IG0601    Added text regarding use of wildcards for
                      context identifiers.  (This information
                      already appeared in section 8.1.2.  The IG
                      change subsequently disappeared.)
 6.1.1      IG1100    Added ranking of priority values.
 6.2         IGDUB    Deleted definition of signals.
 6.2        GEN0202   Expanded text and diagrams describing
                      multiplexing terminations.
 6.2        TTPOST    Added asterisks to multiplexing diagrams to
                      indicate centre of context.  Added Figure 6a
                      showing cascading of multiplexes.
 6.2.2      IG0601    Added text indicating that ALL does not
                      include ROOT.
 6.2.3      IG1100    Added text clarifying what must be supported
                      to claim support of a package.
 6.2.3      IG1100    Added text indicating what packages a peer can
                      indicate support for, when some of them are
                      extensions of others.
 6.2.4      IG0601    Added text on ability of provisioning to
                      override default values, and need for MGC to
                      audit to learn the provisioned defaults.
 6.2.4      IG0601    Added text indicating effect of omitting
                      specific properties from Descriptors in
                      commands modifying a termination.
                      Contradicted original text saying that omitted
                      properties retain their prior values (still
                      true for entirely-omitted Descriptors).
 6.2.4      GEN0202   Modified above text to restrict it to
                      read/write properties, allow for default
                      behaviour in place of default values if so
                      specified in the property definition.
 6.2.4       IGDUB    Trimmed definition of signals Descriptor in
                      table and inserted cross-reference to section
                      7.1.11.
 6.2.4      IG1100    Added Topology and Error Descriptors to table.

Groves, et al. Standards Track [Page 196] RFC 3525 Gateway Control Protocol June 2003

 6.2.5       IGDUB    Specified error code to return if ROOT used
                      inappropriately.
 7.1.1      IG1100    Added qualification to explanation of effect
                      of missing Audit Descriptor, excepting
                      Subtract.
 7.1.3      GEN0202   Changed "inputs" to "bearers" to be consistent
                      with terminology in 6.2.
 7.1.4      IG0601    Small change to make clear that more than one
                      of Local, Remote, and LocalControl can be
                      included in the default streamId.
 7.1.7      IG0601    Default value for Mode specified to be
                      Inactive.
 7.1.7      GEN0202   Added text requiring processing of media in
                      any of the reserved formats, where more than
                      one has been reserved in a given stream.
 7.1.8       IGDUB    Added restriction to at most one m= line per
                      session description.
 7.1.9      IG0601    Text added to omit request identifier if the
                      EventsDescriptor is empty.  Further text added
                      at end to indicate the effects of an empty
                      EventsDescriptor and an empty
                      EventBufferDescriptor.
 7.1.9      IG0601    Fixed typo for destination of a Notify.
 7.1.9      IG1100    Added note to say event remains active after
                      it has been notified, so long as it is still
                      present in the active Events Descriptor.
 7.1.11      IGDUB    Added definition of signals.
 7.1.11     GEN0202   Modified definition to include example of more
                      complex signal, and added role of signal in
                      media preparation for future signals.
 7.1.11      IGDUB    The timeout completion reason was broadened to
                      include other circumstances where the signal
                      completed on its own.  Text added to indicate
                      that if default signal type changed to TO,
                      duration parameter must be provided.

Groves, et al. Standards Track [Page 197] RFC 3525 Gateway Control Protocol June 2003

 7.1.11     GEN0202   Removed reference to BR signal being "so
                      short" it will stop on its own.  Added text
                      indicating that if the type of a signal is
                      changed to TO, the Duration parameter must be
                      supplied.
 7.1.11     IG1100    Deleted text discussing type of Signals List.
 7.1.12     GEN0202   Improved wording of introductory paragraph and
                      added text making content of returned
                      Descriptor clear.
 7.1.14.2   GEN0202   Added text indicating that when the start
                      timer is set to 0, initial digit timing is
                      disabled and the MG waits indefinitely for
                      digits.
 7.1.14.2   GEN0202   Added text pointing out that default digit
                      timer values should be provisioned, but can be
                      overridden in the digit map.
 7.1.14.3   GEN0202   Changed result of long-short digit timer
                      conflict from undefined to long.
 7.1.14.6   IG1100    Clarified that the digit map is provided by
                      the eventDM parameter, which must be present.
 7.1.14.7   GEN0202   Added text clarifying that events covered by
                      the digit map completion event have no side-
                      effects unless separately enabled.
 7.1.14.8   IG0601    Added requirement that the event specification
                      include the eventDM parameter.
 7.1.17      IGDUB    Added text to indicate timestamp is optional
                      and to include observed event parameters in
                      reported content.
 7.1.17     GEN0202   Deleted provision that time is expressed in
                      UTC (since intention was to use format, not
                      time zone).
 7.1.18      IGDUB    Added text indicating error to return if
                      topology option not supported.

Groves, et al. Standards Track [Page 198] RFC 3525 Gateway Control Protocol June 2003

 7.1.18     IG1100    Added text clarifying effect of not mentioning
            TTPOST    a termination in a topology Descriptor, and
                      default topology for a new termination.  (This
                      text got lost between the Dublin meeting and
                      the production of H.248 Amendment 1 out of the
                      Geneva 02/02 meeting.  It has been added back
                      to the present document.)
 7.1.19     IG1100    New section to describe Error Descriptor.
            GEN0202   Slightly edited in Geneva 02/02 meeting.
            ITUPOST   Reference for error code documentation updated
                      to H.248.8.
 7.1.19     IG0601    Added paragraph giving guidance on level at
                      which errors should be reported.
 7.2        IG1100    Noted possibility of Error Descriptor in reply
                      to any command.
 7.2.1      IG1100    Added EventBufferDescriptor as Add parameter.
 7.2.1      IG1100    Removed restriction on use of CHOOSE wildcard.
 7.2.2      IG1100    Added EventBufferDescriptor as Modify
                      parameter.
 7.2.2      GEN0202   Added text on side-effects of Modify of a
                      multiplexing termination.
 7.2.3      IG1100    Added prohibition against subtracting from the
                      NULL context.
 7.2.3      GEN0202   Added text on side-effects of Subtract of a
                      multiplexing termination.
 7.2.3       IGDUB    Added text clarifying effect of empty
                      AuditDescriptor in Subtract.
 7.2.4      IG1100    Added EventBufferDescriptor as Move parameter.
 7.2.4      GEN0202   Removed misleading statement that Move acts as
                      subtract from original context.
 7.2.4      IG1100    Clarified effect of Move on properties of the
                      moved termination.
 7.2.4      GEN0202   Added text on side-effects of Move of a
                      multiplexing termination.

Groves, et al. Standards Track [Page 199] RFC 3525 Gateway Control Protocol June 2003

 7.2.5      IG1100    Added examples showing W- wildcard usage.
 7.2.5      IG1100    Noted that returning a list of all contextIDs
                      requires that they be returned one per
                      ActionReply.
 7.2.5      IG1100    Added table entry (ALL, specific) to determine
                      context in which termination currently
                      resides.
 7.2.6      GEN0202   Added table similar to that in 7.2.5.
 7.2.7      IG0601    Added TerminationID to API.
 7.2.7       IGDUB    Indicated timestamp was optional in Notify, to
                      accord with syntax.
 7.2.7      IG1100    Noted possibility of sending Error Descriptor
                      in Notify.
 7.2.8      IG0601    Added text to description of Forced method to
                      indicate that Forced on ROOT indicates a cold
                      restart (all context state lost).
 7.2.8       IGDUB    Amplified explanation of Disconnected method
                      to emphasize return to the previously
                      controlling MGC.
 7.2.8      IG0601    Added text for MG use of Failover method when
                      it detects MGC failure.
 7.2.8      IG1100    Added notes discouraging use of
                      ServiceChangeAddress and warning that it could
                      be either a full address or just a port
                      number.
 7.2.8      IG0601    Added text indicating that timestamp does not
                      necessarily represent absolute time, only
                      local clock reading.
 7.2.8       IGDUB    Corrected "gateway" to "MGC" in discussion of
                      returned ServiceChangeMgcId parameter.
 7.3        IG0601    Removed error code documentation to Annex L
            ITUPOST   (now H.248.8).
 8          IG1100    Added requirement that an Action be non-empty.

Groves, et al. Standards Track [Page 200] RFC 3525 Gateway Control Protocol June 2003

 8          GEN0202   Added context properties and context property
                      audit requests to commands as potential
                      contents of actions.
 8.1.2      GEN0202   Added prohibition on using partial contextIDs
                      with ALL wildcards.
 8.2.2      IG1100    Added text clarifying when in transaction
                      processing the requested actions have been
                      completed and a reply can be sent.
 8.2.2      IG1100    Added ALL as allowed contextID in
                      TransactionReply.
 8.2.2      GEN0202   Provided general reference to section 7.1.19
                      for generation of error Descriptors.
 8.2.2      IG0601    Corrected Actions to Commands when discussing
                      partially-understood action.
 8.3        IG0601    Added text specifying that the same MId value
                      must be used by a given entity throughout the
                      life of a control association.
 8.3        IG0601    Added text expanding on independence of
                      transactions from messages.
 9          ITUPOST   Indicated that additional transports may be
                      defined in separate Recommendations as well as
                      annexes to the primary specification.
 9          IG0601    Gave specific example of "request source
                      address" for IP.
 9.1        IG1100    Deleted restriction to one outstanding Notify
                      command on a termination at one time, since
                      this is transport-specific.
 9.1        IG0601    Restored restriction, but noted that it
                      applied only to transport not guaranteeing
                      ordered delivery.
 10.2       IG1100    Corrected length of synthesized address field
                      from 10 to 20 hex digits and indicated that
                      calculation should be over entire message, not
                      just one transaction.

Groves, et al. Standards Track [Page 201] RFC 3525 Gateway Control Protocol June 2003

 11.2       IG1100    Corrected text in first two paragraphs
                      describing use of ServiceChangeMgcId
                      parameter.
 11.2       IG1100    Corrected "Transaction Accept" to "Transaction
                      Reply".
 11.4       IG0601    Noted that support of redundant MGs requires
            GEN0202   use of a reliable transport and support in the
                      MGC.  Added more explanation in Geneva.
 11.5       IG0601    Added text clarifying procedure if MG unable
                      to establish a control relationship with any
                      of its eligible MGCs.
 11.5        IGDUB    Added text indicating that when trying to
                      reestablish contact with the previously
                      controlling MGC the MG uses the Disconnected
                      method.
 11.5       IG1100    Clarified handoff procedure.
 11.5       GEN0202   Changed text on replies to transactions in
                      progress during handoff.  Replies now
                      discarded when the service relationship with
                      the old MGC has ended, rather than sent to the
                      new MGC.  The new MGC could still send replies
                      to requests sent to the old MGC.
 12.1.1     GEN0202   Added optional package designation as
                      "designed to be extended only".
 12.1.1     IG1100    Made prohibition on overloading of identifiers
                      in extended packages transitive through all
                      ancestors of the extended package.
 12.1.2      IGDUB    Clarified the set of types allowed for
                      properties.
 12.1.2     GEN0202   Added requirement to specify the base type of
                      a sub-list.
 12.1.2     GEN0202   Provided requirements for content of the
                      "Possible Values" template item, including
                      specification of default values or behaviour.

Groves, et al. Standards Track [Page 202] RFC 3525 Gateway Control Protocol June 2003

 12.1.4     GEN0202   Added requirement to specify the default
                      signal type, and specify a default duration
                      for TO signals.  Also noted that duration is
                      meaningless for BR, and that the signal type
                      might be dependent on the values of other
                      signal parameters.
 12.2       GEN0202   Fixed section title (covers only event and
                      signal parameters, not properties or
                      statistics).
 12.2       IG1100    Reserved SPA and EPA prefixes, so they are not
                      to be used for signal and event parameter
                      tokens.
 12.2       IG0601    Expanded list of reserved prefixes.
 12.2        IGDUB    Clarified the set of types allowed for signal
                      and event parameters.
 12.2       GEN0202   Added requirement to specify the base type of
                      a sub-list.
 12.2       GEN0202   Provided requirements for content of the
                      "Possible Values" template item, including
                      specification of default values or behaviour.
 12.4        IGDUB    Corrected to indicate identifiers must start
                      with alphabetic rather than alphanumeric
                      character.
 13.1       IG0601    Changed private range of binary package
                      identifiers to convenient hex values.
 A          GEN0202   Removed versions from X.680 and X.690
                      references.
 A.2         IGDUB    Added note warning that the syntax alone does
                      not provide a complete description of the
                      constraints, but must be supplemented by a
                      reading of the text and comments.
 A.2        IG0601    Added description of double wrapping of
                      parameters declared as OCTET STRING.

Groves, et al. Standards Track [Page 203] RFC 3525 Gateway Control Protocol June 2003

 A.2        GEN0202   Some editing of double wrapping description to
                      use ASN.1, BER in their proper places.  Added
                      possibility of encoding strings as UTF8String,
                      but only if they contain non-ASCII characters.
 A.2         IGDUB    Added line in table on double wrapping of true
                      octet strings.
 A.2        IG1100    Corrected and expanded comments describing
                      mtpAddress form of MId.  Fixed maximum length
                      of mtpAddress both here and in
                      ServiceChangeAddress.
 A.2        IG0601   Inserted missing lines in IP4Address
                      production.
 A.2        IG0601    Modified TransactionResponseAck to allow
                      acknowledgement of multiple ranges of
                      transactionIds.
 A.2        IG0601    Corrected numerical value of CHOOSE as a
                      context identifier.
 A.2         IGDUB    Added missing extension marker in
                      TopologyRequest.
 A.2        IG1100    AuditReply and AuditResult modified to bring
                      binary functionality into line with text
                      functionality.
 A.2        IG0601    Removed OPTIONAL tag from terminationID in
                      NotifyReply.
 A.2        IG0601    Added extraInfo substructure to EventParameter
                      and SigParameter.
 A.2        IG0601    Modified MediaDescriptor to make it optional
                      to specify a stream.
 A.2        IG0601    Added OPTIONAL tags to reserveValue and
                      reserveGroup.
 A.2         IGDUB    Added to comments for pkgdName to indicate
                      applicability to event names, signal names,
                      and statisticIds as well as property.

Groves, et al. Standards Track [Page 204] RFC 3525 Gateway Control Protocol June 2003

 A.2        IG0601    RequestID made optional in EventsDescriptor
                      and SecondEventsDescriptor and comment added
                      saying it must be present if events are
                      present.
 A.2        IG1100    Added OPTIONAL tags on RequestActions and
                      SecondRequestedActions keepActive BOOLEANs.
 A.2        IG1100    Added comment to indicate requestID value to
                      use in an AuditCapReply.
 A.2        GEN0202   Added comment to DigitMapValue indicating time
                      units for timers.
 A.2        IG0601    Added comment indicating coding of Value for
            GEN0202   ServiceChangeReason.  Cleaned up in Geneva to
                      use ASN.1 and BER in their proper places.
 A.2        IG0601    Inserted missing extension marker in
                      ServiceChangeParm production.
 A.2        IG0601    Aligned definition of mtpAddress in
                      ServiceChangeAddress with that in MId.
 A.2        IG0601    Added timestamp to ServiceChangeResParm.
 A.2         IGDUB    Changed type of profileName in
                      ServiceChangeProfile to IA5String.
 A.2        IG0601    Made returned value optional in
                      statisticsParameter, to support
                      auditCapability result.
 A.2        GEN0202   Added reference to ISO 8601:1988 for
                      TimeNotation.
 A.2        IG1100    Value production modified to support the
                      sublist parameter type.
 A.3        IG1100    Corrected ABNF for digitStringlisT, replacing
                      "/" with "|".
 A.3        IG1100    Added parentheses to digitMapRange production.
 A.3        IG1100    Replaced more abbreviated syntax for pathName
                      with fuller definition and constraints copied
                      from B.2.

Groves, et al. Standards Track [Page 205] RFC 3525 Gateway Control Protocol June 2003

 B.2         IGDUB    Added note warning that the syntax alone does
                      not provide a complete description of the
                      constraints, but must be supplemented by a
                      reading of the text and comments.
 B.2        IG0601    Added note warning that the interpretation of
                      symbols is context-dependent.
 B.2        IG1100    Added comment to indicate case insensitivity
                      of protocol (excepting SDP) and ABNF.
 B.2        IG0601    Expanded upon and capitalized this comment.
 B.2        IG0601    Lengthy note added on the coding of the VALUE
                      construct.
 B.2         IGDUB    Deleted sentence in note suggesting that
                      packages could add new types for properties,
                      parameters, or statistics.
 B.2        IG0601    Added note indicating that parsers should
                      allow for white space preceding the first line
                      of SDP in Local or Remote.
 B.2         IGDUB    Added comments identifying the O- and W- tags.
 B.2        IG1100    Moved wildcard tag up from individual commands
                      to commandRequestList.
 B.2        GEN0202   Added additional error case to actionReply.
 B.2        IG0601    Modified syntax of auditOther to allow return
                      of terminationID only.
 B.2         IGDUB    Corrected upper limit for V4hex.
 B.2        IG1100    Corrected and expanded comments describing
                      mtpAddress form of MId.
 B.2        IG0601    Modified comment to mediaParm to make
                      streamParms and StreamDescriptor mutually
                      exclusive.
 B.2        GEN0202   Modified comment further to indicate at most
                      one instance of terminationStateDescriptor.
 B.2        GEN0202   Expanded comment for streamParm to indicate
                      the restriction on repetition is per item.

Groves, et al. Standards Track [Page 206] RFC 3525 Gateway Control Protocol June 2003

 B.2        IG0601    Modified "at most once" comments to localParm,
                      terminationStateParm, and modemType, to allow
                      multiple instances of propertyParm in the
                      first two cases and extensionParameter in the
                      last one.
 B.2        IG0601    Added note before description of Local and
                      Remote, pointing out that the octet value x00
                      is not allowed in octetString.
 B.2        IG0601    Syntax for eventsDescriptor, embedFirst, and
                      eventBufferDescriptor modified to make
                      contents beyond token optional.
 B.2         IGDUB    Replaced "event" by "item" in comment to
                      pkgdName because pkgdName applies to
                      properties, signals, and statistics as well.
 B.2        IG0601    Corrected placement of EQUAL in eventDM
                      production.
 B.2        IG1100    Added comment and syntax to indicate requestID
                      value to use in an AuditCapReply.
 B.2        IG1100    Corrected Modem Descriptor to allow package
                      items as properties.
 B.2        IG0601    Comment to modemType changed to allow multiple
                      instances of extensionParameter.
 B.2        GEN0202   Comment added to indicate units for Timer.
 B.2        IG1100    Added parentheses to digitMapRange production.
 B.2        IG1100    Added comment to serviceChangeParm,
                      restricting each parameter to one appearance.
 B.2        IG0601    Added comments making serviceChangeMgcId and
                      serviceChangeAddress mutually exclusive in
                      ServiceChangeParm and servChgReplyParm.
 B.2         IGDUB    Added comment to serviceChangeParm indicating
                      that ServiceChangeMethod and
                      ServiceChangeReason are required.
 B.2        IG0601    Added Timestamp to servChgReplyParm.

Groves, et al. Standards Track [Page 207] RFC 3525 Gateway Control Protocol June 2003

 B.2        IG0601    Added comment indicating coding of Value for
                      ServiceChangeReason.
 B.2        IG0601    Modified ServiceChangeAddress to use MId
                      definition for full address.
 B.2        IG1100    Made returned value optional in
                      statisticsParameter, to support
                      auditCapability result.
 B.2        IG1100    Changed topologyDescriptor to allow multiple
                      triples.
 B.2        IG0601    Added comment forbidding use of a double quote
                      within a quotedString value.
 B.2        IG1100    Reserved prefixes for new tokens added to
                      signalParameter and eventParameter, to avoid
                      collision with package names.
 B.2        IG1100    EmbedToken and EmergencyToken changed to
                      remove clash with EventBufferToken.
 B.3        IG1100    New section describing hexadecimal octet
                      encoding.
 B.4        IG1100    New section describing hex octet sequence.
 C          IG1100    Added permission to use Annex C properties in
                      LocalControl as well as in Local and Remote.
 C          IG0601    Added text making support of all properties of
                      Annex C optional.
 C           IGDUB    Added directions to reconcile tabulated
                      formats with allowed types for properties.
 C.1        IG1100    Corrected Q.765 reference to Q.765.5 for
                      ACodec.
 C.1        IG1100    Deprecated Echocanc codepoint in favour of
                      package-defined property.
 C.4        ITUPOST   Updated references from Q.2961 to Q.2961.1.
 C.4         IGDUB    Added details on format of VPVC.
 C.9        IG1100    Renamed USI to layer1prot.

Groves, et al. Standards Track [Page 208] RFC 3525 Gateway Control Protocol June 2003

 C.9        IG1100    Deprecated ECHOCI codepoint in favour of
                      package-defined property.
 C.9        IG1100    Added new USI property.
 C.11       IG1100    Added m= line tag.
 D.1        IG0601    Added explanation of ALF.
 D.1.5       IGDUB    Expanded text indicating that when trying to
                      reestablish contact with the previously
                      controlling MGC the MG uses the Disconnected
                      method.
 E.1.2      GEN0202   Added missing EventsDescriptor parameters
                      lines.
 E.1.2      GEN0202   For the Signal Completion event:
                      - corrected the description of how it is
                      enabled
                      - heavily edited the description of the Signal
                      Identity observed event parameter and added a
                      type.
 E.1.2       IGDUB    The timeout completion reason for the Signal
                      Completion event was broadened to include
                      other circumstances where the signal completed
                      on its own.
 E.1.2      IG1100    Added signal list ID observed event parameter
                      to the Signal Completion event.
 E.2.1      IG0601    Added missing read only, read-write
                      specifications.
 E.2.1      IG0601    Split ProvisionalResponseTimer properties into
                      one for MG, one for MGC.
 E.3        GEN0202   Added "Designed to be extended only" to
                      tonegen package description.
 E.4        GEN0202   Added "Designed to be extended only" to
                      tonedet package description.
 E.4.2      GEN0202   Added type for tone ID observed parameter for
                      Long Tone Detected event.

Groves, et al. Standards Track [Page 209] RFC 3525 Gateway Control Protocol June 2003

 E.6.2      IG1100    Corrected binary identifier for digit map
                      completion event to avoid clash with base
                      package.
 E.6.2      IG1100    Removed procedural text.
 E.6.5      IG1100    Added procedural text indicating where to find
                      the applicable digit map and indicating the
                      error to return if the parameter is missing.
 E.6.5      IG0601    Further modified procedural text.
 E.7.3      IG1100    Corrected text identifier for payphone
                      recognition tone to avoid clash with base
                      package.
 E.10.5      IGDUB    Provided informative references for tones and
                      procedures for continuity check.
 E.13       GEN0202   Added note that TDM package could also apply
                      to other transports.
 E.13.1     IG1100    Changed default for echo cancellation from
                      "on" to provisioned.
 E.13.1     IG0601    Corrected type for gain property.
 Appendix   TTPOST    Included a number of corrections which were
    I                 not picked up in H.248.1 Amendment 1 but which
                      do appear in H.248.1 v2.

Intellectual Property Rights

 The ITU draws attention to the possibility that the practice or
 implementation of this RFC may involve the use of a claimed
 Intellectual Property Right.  The ITU takes no position concerning
 the evidence, validity or applicability of claimed Intellectual
 Property Rights, whether asserted by ITU members or others outside of
 the Recommendation development process.
 As of the date of approval of this RFC, the ITU had received notice
 of intellectual property, protected by patents, which may be required
 to implement this RFC.  However, implementors are cautioned that this
 may not represent the latest information and are therefore strongly
 urged to consult the TSB patent database.

Groves, et al. Standards Track [Page 210] RFC 3525 Gateway Control Protocol June 2003

 The IETF has also received notice of intellectual property claims
 relating to Megaco/H.248.1.  Please consult the IETF IPR
 announcements at http://www.ietf.org/ipr.html.

Acknowledgments

 Megaco/H.248.1 is the result of hard work by many people in both the
 IETF and in ITU-T Study Group 16.  This section records those who
 played a prominent role in ITU-T meetings, on the Megaco list, or
 both.
 Megaco/H.248 owes a large initial debt to the MGCP protocol (RFC
 2705), and thus to its authors, Mauricio Arango, Andrew Dugan, Ike
 Elliott, Christian Huitema, and Scott Pickett.  Flemming Andreasen
 does not appear on this list of authors, but was a major contributor
 to the development of both MGCP and Megaco/H.248.1.  RFC 3435 has an
 extensive acknowledgement of many other people who worked on media
 gateway control before Megaco got started.
 The authors of the first Megaco RFCs (2805, then 3015) were Fernando
 Cuervo, Nancy Greene, Abdallah Rayhan, Christian Huitema, Brian
 Rosen, and John Segers.  Christian Groves conceived and was editor of
 Annex C.  The people most active on the Megaco list in the period
 leading up to the completion of RFC 2885 were Brian Rosen, Tom
 Taylor, Nancy Greene, Christian Huitema, Matt Holdrege, Chip Sharp,
 John Segers, Michael Thomas, Henry Sinnreich, and Paul Sijben.  The
 people who sacrificed sleep and meals to complete the massive amount
 of work required in the decisive Study Group 16 meeting of February,
 2000, were Michael Brown, Ranga Dendi, Larry Forni, Glen Freundlich,
 Christian Groves, Alf Heidemark, Steve Magnell, Selvam Rengasami,
 Rich Rubin, Klaus Sambor, John Segers, Chip Sharp, Tom Taylor, and
 Stephen Terrill.
 The most active people on the Megaco list in the period since the
 February 2000 have been Tom Taylor, Brian Rosen, Christian Groves,
 Madhu Babu Brahmanapally, Troy Cauble, Terry Anderson, Chuong Nguyen,
 and Kevin Boyle, but many other people have been regular
 contributors.  Brian Rosen did tremendous service in putting together
 the Megaco interoperability tests.  On the Study Group 16 side, the
 editorial team for the final revised document in February, 2002
 included Christian Groves, Marcello Pantaleo, Terry Anderson, Peter
 Leis, Kevin Boyle, and Tom Taylor.
 Tom Taylor as Megaco Chair managed the day to day operation of the
 Megaco list, with Brian Rosen taking an equal share of the burden for
 most of the last three years.  Glen Freundlich as the Study Group 16
 Rapporteur ran the ITU-T meetings and ensured that all of the work at
 hand was completed.  Without Glen's determination the Megaco/H.248

Groves, et al. Standards Track [Page 211] RFC 3525 Gateway Control Protocol June 2003

 standard would have taken at least half a year longer to produce.
 Christian Groves filled in ably as Rapporteur when Glen could no
 longer take part.

Authors' Addresses

 Terry L. Anderson
 24 Hill St
 Bernardsville, NJ 07924
 USA
 EMail: tlatla@verizon.net
 Christian Groves
 Ericsson AsiaPacificLab Australia
 37/360 Elizabeth St
 Melbourne, Victoria 3000
 Australia
 EMail: Christian.Groves@ericsson.com.au
 Marcello Pantaleo
 Ericsson Eurolab Deuschland
 Ericsson Allee 1
 52134 Herzogenrath, Germany
 EMail: Marcello.Pantaleo@eed.ericsson.se
 Tom Taylor
 Nortel Networks
 1852 Lorraine Ave,
 Ottawa, Ontario
 Canada K1H 6Z8
 Phone: +1 613 736 0961
 EMail: taylor@nortelnetworks.com

Groves, et al. Standards Track [Page 212] RFC 3525 Gateway Control Protocol June 2003

Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Groves, et al. Standards Track [Page 213]

/data/webs/external/dokuwiki/data/pages/rfc/rfc3525.txt · Last modified: 2003/06/05 22:27 (external edit)