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rfc:rfc2885

Network Working Group F. Cuervo Request for Comments: 2885 N. Greene Category: Standards Track Nortel Networks

                                                            C. Huitema
                                                 Microsoft Corporation
                                                             A. Rayhan
                                                       Nortel Networks
                                                              B. Rosen
                                                               Marconi
                                                             J. Segers
                                                   Lucent Technologies
                                                           August 2000
                    Megaco Protocol version 0.8

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 (2000).  All Rights Reserved.

Abstract

 This document is common text with Recommendation H.248 as
 redetermined in Geneva, February 2000.  It must be read in
 conjunction with the Megaco Errata, RFC 2886.  A merged document
 presenting the Megaco protocol with the Errata incorporated will be
 available shortly.
 The protocol presented in this document meets the requirements for a
 media gateway control protocol as presented in RFC 2805.

Cuervo, et al. Standards Track [Page 1] RFC 2885 Megaco Protocol August 2000

TABLE OF CONTENTS

 1. SCOPE..........................................................6
 2. REFERENCES.....................................................6
 2.1 Normative references..........................................6
 2.2 Informative references........................................8
 3. DEFINITIONS....................................................9
 4. ABBREVIATIONS.................................................10
 5. CONVENTIONS...................................................11
 6. CONNECTION MODEL..............................................11
 6.1 Contexts.....................................................14
      6.1.1 Context Attributes and Descriptors....................15
      6.1.2 Creating, Deleting and Modifying Contexts.............15
 6.2 Terminations.................................................15
      6.2.1 Termination Dynamics..................................16
      6.2.2 TerminationIDs........................................17
      6.2.3 Packages..............................................17
      6.2.4 Termination Properties and Descriptors................18
      6.2.5 Root Termination......................................20
 7. COMMANDS......................................................20
 7.1 Descriptors..................................................21
      7.1.1 Specifying Parameters.................................21
      7.1.2 Modem Descriptor......................................22
      7.1.3 Multiplex Descriptor..................................22
      7.1.4 Media Descriptor......................................23
      7.1.5 Termination State Descriptor..........................23
      7.1.6 Stream Descriptor.....................................24
      7.1.7 LocalControl Descriptor...............................24
      7.1.8 Local and Remote Descriptors..........................25
      7.1.9 Events Descriptor.....................................28
      7.1.10 EventBuffer Descriptor...............................31
      7.1.11 Signals Descriptor...................................31
      7.1.12 Audit Descriptor.....................................32
      7.1.13 ServiceChange Descriptor.............................33
      7.1.14 DigitMap Descriptor..................................33
      7.1.15 Statistics Descriptor................................38
      7.1.16 Packages Descriptor..................................39
      7.1.17 ObservedEvents Descriptor............................39
      7.1.18  Topology Descriptor.................................39
 7.2 Command Application Programming Interface....................42
      7.2.1 Add...................................................43
      7.2.2 Modify................................................44
      7.2.3 Subtract..............................................45
      7.2.4 Move..................................................46
      7.2.5 AuditValue............................................47
      7.2.6 AuditCapabilities.....................................48
      7.2.7 Notify................................................49
      7.2.8 ServiceChange.........................................50

Cuervo, et al. Standards Track [Page 2] RFC 2885 Megaco Protocol August 2000

      7.2.9 Manipulating and Auditing Context Attributes..........54
      7.2.10 Generic Command Syntax...............................54
 7.3 Command Error Codes..........................................55
 8. TRANSACTIONS..................................................56
 8.1 Common Parameters............................................58
      8.1.1 Transaction Identifiers...............................58
      8.1.2 Context Identifiers...................................58
 8.2 Transaction Application Programming Interface................58
      8.2.1 TransactionRequest....................................59
      8.2.2 TransactionReply......................................59
      8.2.3 TransactionPending....................................60
 8.3 Messages.....................................................61
 9. TRANSPORT.....................................................61
 9.1 Ordering of Commands.........................................62
 9.2 Protection against Restart Avalanche.........................63
 10. SECURITY CONSIDERATIONS......................................64
 10.1 Protection of Protocol Connections..........................64
 10.2 Interim AH scheme...........................................65
 10.3 Protection of Media Connections.............................66
 11.  MG-MGC CONTROL INTERFACE....................................66
 11.1 Multiple Virtual MGs........................................67
 11.2 Cold Start..................................................68
 11.3 Negotiation of Protocol Version.............................68
 11.4 Failure of an MG............................................69
 11.5 Failure of an MGC...........................................69
 12. PACKAGE DEFINITION...........................................70
 12.1 Guidelines for defining packages............................71
      12.1.1 Package..............................................71
      12.1.2 Properties...........................................72
      12.1.3 Events...............................................72
      12.1.4 Signals..............................................73
      12.1.5 Statistics...........................................73
      12.1.6 Procedures...........................................73
 12.2 Guidelines to defining Properties, Statistics and Parameters
      to Events and Signals.......................................73
 12.3 Lists.......................................................74
 12.4 Identifiers.................................................74
 12.5 Package Registration........................................74
 13.  IANA CONSIDERATIONS.........................................74
 13.1 Packages....................................................74
 13.2 Error Codes.................................................75
 13.3 ServiceChange Reasons.......................................76
 ANNEX A: BINARY ENCODING OF THE PROTOCOL (NORMATIVE).............77
 A.1 Coding of wildcards..........................................77
 A.2 ASN.1 syntax specification...................................78
 A.3 Digit maps and path names....................................94
 ANNEX B TEXT ENCODING OF THE PROTOCOL (NORMATIVE)................95
 B.1 Coding of wildcards..........................................95

Cuervo, et al. Standards Track [Page 3] RFC 2885 Megaco Protocol August 2000

 B.2 ABNF specification...........................................95
 ANNEX C TAGS FOR MEDIA STREAM PROPERTIES (NORMATIVE)............107
 C.1 General Media Attributes....................................107
 C.2 Mux Properties..............................................108
 C.3 General bearer properties...................................109
 C.4 General ATM properties......................................109
 C.5 Frame Relay.................................................112
 C.6 IP..........................................................113
 C.7 ATM AAL2....................................................113
 C.8 ATM AAL1....................................................114
 C.9 Bearer Capabilities.........................................116
 C.10 AAL5 Properties............................................123
 C.11 SDP Equivalents............................................124
 C.12 H.245......................................................124
 ANNEX D TRANSPORT OVER IP (NORMATIVE)...........................125
 D.1 Transport over IP/UDP using Application Level Framing.......125
      D.1.1 Providing At-Most-Once Functionality.................125
      D.1.2 Transaction identifiers and three-way handshake......126
              D.1.2.1 Transaction identifiers....................126
              D.1.2.2 Three-way handshake........................126
      D.1.3 Computing retransmission timers......................127
      D.1.4 Provisional responses................................128
      D.1.5 Repeating Requests, Responses and Acknowledgements...128
 D.2  using TCP..................................................130
         D.2.1 Providing the At-Most-Once functionality..........130
         D.2.2 Transaction identifiers and three way handshake...130
         D.2.3 Computing retransmission timers...................131
         D.2.4 Provisional responses.............................131
         D.2.5 Ordering of commands..............................131
 ANNEX E BASIC PACKAGES..........................................131
 E.1 Generic.....................................................131
      E.1.1 Properties...........................................132
      E.1.2 Events...............................................132
      E.1.3 Signals..............................................133
      E.1.4 Statistics...........................................133
 E.2 Base Root Package...........................................133
      E.2.1 Properties...........................................134
      E.2.2 Events...............................................135
      E.2.3 Signals..............................................135
      E.2.4 Statistics...........................................135
      E.2.5 Procedures...........................................135
 E.3 Tone Generator Package......................................135
      E.3.1 Properties...........................................135
      E.3.2 Events...............................................136
      E.3.3 Signals..............................................136
      E.3.4 Statistics...........................................136
      E.3.5 Procedures...........................................136
 E.4 Tone Detection Package......................................137

Cuervo, et al. Standards Track [Page 4] RFC 2885 Megaco Protocol August 2000

      E.4.1 Properties...........................................137
      E.4.2 Events...............................................137
      E.4.3 Signals..............................................139
      E.4.4 Statistics...........................................139
      E.4.5 Procedures...........................................139
 E.5 Basic DTMF Generator Package................................140
      E.5.1 Properties...........................................140
      E.5.2 Events...............................................140
      E.5.3 Signals..............................................140
      E.5.4 Statistics...........................................141
      E.5.5 Procedures...........................................141
 E.6 DTMF detection Package......................................141
      E.6.1 Properties...........................................142
      E.6.2 Events...............................................142
      E.6.3 Signals..............................................143
      E.6.4 Statistics...........................................143
      E.6.5 Procedures...........................................143
 E.7 Call Progress Tones Generator Package.......................143
      E.7.1 Properties...........................................144
      E.7.2 Events...............................................144
      E.7.3 Signals..............................................144
      E.7.4 Statistics...........................................145
      E.7.5 Procedures...........................................145
 E.8 Call Progress Tones Detection Package.......................145
      E.8.1 Properties...........................................145
      E.8.2 Events...............................................145
      E.8.3 Signals..............................................145
      E.8.4 Statistics...........................................145
      E.8.5 Procedures...........................................146
 E.9 Analog Line Supervision Package.............................146
      E.9.1 Properties...........................................146
      E.9.2 Events...............................................146
      E.9.3 Signals..............................................147
      E.9.4 Statistics...........................................148
      E.9.5 Procedures...........................................148
 E.10 Basic Continuity Package...................................148
      E.10.1 Properties..........................................148
      E.10.2 Events..............................................148
      E.10.3 Signals.............................................149
      E.10.4 Statistics..........................................150
      E.10.5 Procedures..........................................150
 E.11 Network Package............................................150
      E.11.1 Properties..........................................150
      E.11.2 Events..............................................151
      E.11.3 Signals.............................................152
      E.11.4 Statistics..........................................152
      E.11.5 Procedures..........................................153
 E.12 RTP  Package...............................................153

Cuervo, et al. Standards Track [Page 5] RFC 2885 Megaco Protocol August 2000

      E.12.1 Properties..........................................153
      E.12.2 Events..............................................153
      E.12.3 Signals.............................................153
      E.12.4 Statistics..........................................153
      E.12.5 Procedures..........................................154
 E.13 TDM Circuit Package........................................154
      E.13.1 Properties..........................................155
      E.13.2 Events..............................................155
      E.13.3 Signals.............................................155
      E.13.4 Statistics..........................................156
      E.13.5 Procedures..........................................156
 APPENDIX A EXAMPLE CALL FLOWS (INFORMATIVE).....................157
 A.1 Residential Gateway to Residential Gateway Call.............157
      A.1.1 Programming Residential GW Analog Line Terminations for
      Idle Behavior..............................................157
      A.1.2 Collecting Originator Digits and Initiating Termination
      ...........................................................159
 Authors' Addresses..............................................168
 Full Copyright Statement........................................170

1. SCOPE

 This document defines the protocol 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 H.246. This
 recommendation does not define how gateways, multipoint control units
 or integrated 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 SCN signalling systems,
 including tone signalling, ISDN, ISUP, QSIG, and GSM.  National
 variants of these signalling systems will be supported where
 applicable.
 The protocol definition in this document is common text with ITU-T
 Recommendation H.248.  It meets the requirements documented in RFC
 2805.

2. REFERENCES

2.1 Normative references

 ITU-T Recommendation H.225.0 (1998): "Call Signalling Protocols and
 Media Stream Packetization for Packet Based Multimedia Communications
 Systems".

Cuervo, et al. Standards Track [Page 6] RFC 2885 Megaco Protocol August 2000

 ITU-T Recommendation H.235 (02/98): "Security and encryption for
 H-Series (H.323 and other H.245-based) multimedia terminals".
 ITU-T Recommendation H.245 (1998): "Control Protocol for Multimedia
 Communication".
 ITU-T Recommendation H.323 (1998): "Packet Based Multimedia
 Communication Systems".
 ITU-T Recommendation I.363.1 (08/96), "B-ISDN ATM Adaptation Layer
 specification: Type 1 AAL".
 ITU-T Recommendation I.363.2 (09/97), "B-ISDN ATM Adaptation Layer
 specification: Type 2 AAL".
 ITU-T Recommendation I.363.5 (08/96), "B-ISDN ATM Adaptation Layer
 specification: Type 5 AAL".
 ITU-T Recommendation I.366.1 (06/98), "Segmentation and Reassembly
 Service Specific Convergence Sublayer for the AAL type 2".
 ITU-T Recommendation I.366.2 (02/99), "AAL type 2 service specific
 convergence sublayer for trunking".
 ITU-T Recommendation I.371 (08/96), "Traffic control and congestion
 control in B-ISDN".
 ITU-T Recommendation Q.763 (09/97), "Signalling System No. 7 - ISDN
 user part formats and codes".
 ITU-T Recommendation Q.765, "Signalling System No. 7 - Application
 transport mechanism".
 ITU-T Recommendation Q.931 (05/98): "Digital Subscriber Signalling
 System No.  1 (DSS 1) - ISDN User-Network Interface Layer 3
 Specification for Basic Call Control".
 ITU-T Recommendation Q.2630.1 (1999), "AAL Type 2 Signalling Protocol
 (Capability Set 1)".
 ITU-T Recommendation Q.2931 (10/95), "Broadband Integrated Services
 Digital Network (B-ISDN) - Digital Subscriber Signalling System No.
 2 (DSS 2) - User-Network Interface (UNI) - Layer 3 specification for
 basic call/connection control".
 ITU-T Recommendation Q.2941.1 (09/97), "Digital Subscriber Signalling
 System No. 2 - Generic Identifier Transport".

Cuervo, et al. Standards Track [Page 7] RFC 2885 Megaco Protocol August 2000

 ITU-T Recommendation Q.2961 (10/95), "Broadband integrated services
 digital network (B-ISDN) - Digital subscriber signalling system no.2
 (DSS 2) - additional traffic parameters".
 ITU-T Recommendation Q.2961.2 (06/97), "Digital subscriber signalling
 system No. 2 - Additional traffic parameters: Support of ATM transfer
 capability in the broadband bearer capability information element."
 ITU-T Recommendation X.213 (11/1995), "Information technology - Open
 System Interconnection - Network service definition plus Amendment 1
 (08/1997), Addition of the Internet protocol address format
 identifier".
 ITU-T Recommendation V.76 (08/96), "Generic multiplexer using V.42
 LAPM-based procedures".
 ITU-T Recommendation X.680 (1997): "Information technology-Abstract
 Syntax Notation One (ASN.1): Specification of basic notation".
 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".
 Rose, M. and D. Cass, "ISO Transport Service on top of the TCP,
 Version 3", RFC 1006, May 1987.
 Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications:
 ABNF", RFC 2234, November 1997.
 Handley, M. and  V. Jacobson, "SDP: Session Description Protocol",
 RFC 2327, April 1998.
 Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
 November 1998.
 Kent, S. and R. Atkinson, "IP Encapsulating Security Payload (ESP)",
 RFC 2406, November 1998.

2.2 Informative references

 ITU-T Recommendation E.180/Q.35 (1998): "Technical characteristics of
 tones for the telephone service".
 CCITT Recommendation G.711 (1988), "Pulse Code Modulation (PCM) of
 voice frequencies".
 ITU-T Recommendation H.221 (05/99),"Frame structure for a 64 to 1920
 kbit/s channel in audiovisual teleservices".

Cuervo, et al. Standards Track [Page 8] RFC 2885 Megaco Protocol August 2000

 ITU-T Recommendation H.223 (1996), "Multiplexing protocol for low bit
 rate multimedia communication".
 ITU-T Recommendation Q.724 (1988): "Signalling procedures".
 Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980.
 Postel, J., "Internet protocol", STD 5, RFC 791, September 1981.
 Postel, J., "TRANSMISSION CONTROL PROTOCOL", STD 7, RFC 793,
 September 1981.
 Simpson, W., "The Point-to-Point Protocol", STD 51, RFC 1661, July
 1994.
 Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A
 Transport Protocol for Real-Time Applications", RFC 1889, January
 1996.
 Schulzrinne, H., "RTP Profile for Audio and Video Conferences with
 Minimal Control", RFC 1890, January 1996.
 Kent, S. and R. Atkinson, "Security Architecture for the Internet
 Protocol", RFC 2401, November 1998.
 Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
 Specification", RFC 2460, December 1998.
 Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg, "SIP:
 Session Initiation Protocol", RFC 2543, March 1999.
 Greene, N., Ramalho, M. and B. Rosen, "Media Gateway control protocol
 architecture and requirements", RFC 2805, April 1999.

3. DEFINITIONS

 Access Gateway: A type of gateway that provides a User to 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

Cuervo, et al. Standards Track [Page 9] RFC 2885 Megaco Protocol August 2000

 (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 performs other IVR functions, or may
 perform media conferencing.
 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 recommendation defines the following terms.
 ATM          Asynchronous Transfer Mode
 BRI          Basic Rate Interface
 CAS          Channel Associated Signalling
 DTMF         Dual Tone Multi-Frequency
 FAS          Facility Associated Signalling
 GW           GateWay
 IANA         Internet Assigned Numbers Authority
 IP           Internet Protocol
 ISUP         ISDN User Part

Cuervo, et al. Standards Track [Page 10] RFC 2885 Megaco Protocol August 2000

 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 this 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.

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.

Cuervo, et al. Standards Track [Page 11] RFC 2885 Megaco Protocol August 2000

        +------------------------------------------------------+
        |Media Gateway                                         |
        | +-------------------------------------------------+  |
        | |Context                          +-------------+ |  |
        | |                                 | Termination | |  |
        | |                                 |-------------| |  |
        | |  +-------------+             +->| SCN Bearer  |<---+->
        | |  | Termination |   +-----+   |  |   Channel   | |  |
        | |  |-------------|   |     |---+  +-------------+ |  |
      <-+--->| RTP Stream  |---|  *  |                      |  |
        | |  |             |   |     |---+  +-------------+ |  |
        | |  +-------------+   +-----+   |  | Termination | |  |
        | |                              |  |-------------| |  |
        | |                              +->| SCN Bearer  |<---+->
        | |                                 |   Channel   | |  |
        | |                                 +-------------+ |  |
        | +-------------------------------------------------+  |
        |                                                      |
        |                                                      |
        |                    +------------------------------+  |
        |                    |Context                       |  |
        |  +-------------+   |              +-------------+ |  |
        |  | Termination |   | +-----+      | Termination | |  |
        |  |-------------|   | |     |      |-------------| |  |
      <-+->| SCN Bearer  |   | |  *  |------| SCN Bearer  |<---+->
        |  |   Channel   |   | |     |      |   Channel   | |  |
        |  +-------------+   | +-----+      +-------------+ |  |
        |                    +------------------------------+  |
        |                                                      |
        |                                                      |
        | +-------------------------------------------------+  |
        | |Context                                          |  |
        | |  +-------------+                +-------------+ |  |
        | |  | Termination |   +-----+      | Termination | |  |
        | |  |-------------|   |     |      |-------------| |  |
      <-+--->| SCN Bearer  |---|  *  |------| SCN Bearer  |<---+->
        | |  |   Channel   |   |     |      |   Channel   | |  |
        | |  +-------------+   +-----+      +-------------+ |  |
        | +-------------------------------------------------+  |
        | ___________________________________________________  |
        +------------------------------------------------------+
              Figure 1: Example of H.248 Connection Model

Cuervo, et al. Standards Track [Page 12] RFC 2885 Megaco Protocol August 2000

 Figure 1 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.
 The example below 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 below.
        +------------------------------------------------------+
        |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

Cuervo, et al. Standards Track [Page 13] RFC 2885 Megaco Protocol August 2000

        +------------------------------------------------------+
        |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.

Cuervo, et al. Standards Track [Page 14] RFC 2885 Megaco Protocol August 2000

 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:
  .  ContextID.
  .  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.
  .  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.
  .  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.
 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.

Cuervo, et al. Standards Track [Page 15] RFC 2885 Megaco Protocol August 2000

 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.  Signals are MG
 generated media streams such as tones and announcements as well as
 line signals such as hookswitch.  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 section 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 Termination.  The Terminations that
 source/sink the digital channels are connected to a separate
 Termination called the multiplexing Termination. This Termination
 describes the multiplex used (e.g. how the H.221 frames are carried
 over the digital channels used).  The MuxDescriptor is used to this
 end.  If multiple media are carried, this Termination contains
 multiple StreamDescriptors. The media streams can be associated with
 streams sourced/sunk by other Terminations in the Context.
 Terminations may be created which represent multiplexed bearers, such
 as an ATM AAL2.  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 sections. 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.

Cuervo, et al. Standards Track [Page 16] RFC 2885 Megaco Protocol August 2000

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.  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.
 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 a Termination realizes a set of such Packages.
 More information on definition of packages can be found in section
 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,

Cuervo, et al. Standards Track [Page 17] RFC 2885 Megaco Protocol August 2000

 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.

6.2.4 Termination Properties and Descriptors

 Terminations have properties.  The properties have unique
 PropertyIDs.  Most properties have default values.  When a
 Termination is created, properties get their default values, unless
 the controller specifically sets a different value.  The default
 value of a property of a physical Termination can be changed by
 setting it to a different value when the Termination is in the null
 Context.  Every time such a Termination returns to the null Context,
 the values of its properties are reset to this default value.
 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.  Properties not mentioned in the
 command retain their prior values.  Similarly, a property of a
 Termination in a Context may have its value changed by the Modify
 command.  Properties not mentioned in the Modify command retain their
 prior values. 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.
 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.

Cuervo, et al. Standards Track [Page 18] RFC 2885 Megaco Protocol August 2000

 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.
 EventBuffer               Describes events to be detected by the MG
                           when Event Buffering is active.
 Signals                   Describes signals and/or actions to be
                           applied (e.g. Busy Tone) to the
                           Terminations.
 Audit                     In Audit commands, identifies which
                           information is desired.
 Packages                  In AuditValue, returns a list of Packages
                           realized by Termination.
 DigitMap                  Instructions for handling DTMF tones at
                           the MG.
 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.

Cuervo, et al. Standards Track [Page 19] RFC 2885 Megaco Protocol August 2000

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 and events (signals  are not appropriate for root).
 Accordingly, the root TerminationID may appear in:
  .  a Modify command - to change a property or set an event
  .  a Notify command - to report an event
  .  an AuditValue return - to examine the values of properties
     implemented on root
  .  an AuditCapability - to determine what properties of root are
     implemented
  .  a ServiceChange - to declare the gateway in or out of service.
 Any other use of the root TerminationID is an error.

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
 section 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.

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 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.
 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 an 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 sections 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 subsection enumerates
 these Descriptors.  Descriptors may be returned as output from a
 command.  Parameters and parameter usage specific to a given Command
 type are described in the subsection 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_.}.

Cuervo, et al. Standards Track [Page 21] RFC 2885 Megaco Protocol August 2000

 Parameters may be fully specified, over-specified or under-specified:
 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. Under-specified parameters, using the CHOOSE value, allow the
    command responder to choose any value it can support.
 3. Over-specified 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.
 Unspecified mandatory parameters (i.e. mandatory parameters not
 specified in a descriptor) result in the command responder retaining
 the previous value for that parameter.  Unspecified optional
 parameters result in the command responder using the default value of
 the parameter.  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.22bis, V.32,
 V.32bis, 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:
  . H.221
  . H.223,
  . H.226,
  . V.76,
  . Possible Extensions

Cuervo, et al. Standards Track [Page 22] RFC 2885 Megaco Protocol August 2000

 and a set of TerminationIDs representing the multiplexed inputs, in
 order.  For example:
     Mux = H.221{ MyT3/1/2, MyT3/2/13, MyT3/3/6, MyT3/21/22}

7.1.4 Media Descriptor

 The Media Descriptor specifies the parameters for all the media
 streams.  These parameters are structured into two descriptors, a
 Termination State 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
      TerminationStateDescriptor
      Stream Descriptor
              LocalControl Descriptor
              Local Descriptor
              Remote Descriptor
 As a convenience a LocalControl, Local, or Remote descriptor 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 Termination State Descriptor

 The Termination State 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.

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 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:
  .  Alternative Values: multiple values in a list, one of which must
     be selected
  .  Ranges: minimum and maximum values, any value between min and max
     must be selected, boundary values included
  .  Greater Than/Less Than: value must be greater/less than specified
     value
  .  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 section 7.1.9 for details.

7.1.6 Stream Descriptor

 A Stream descriptor specifies the parameters of a single bi-
 directional 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.

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 section 7.1.1.

Cuervo, et al. Standards Track [Page 24] RFC 2885 Megaco Protocol August 2000

 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.  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 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, is SHALL respond with
 error 510 (insufficient resources).
 The default value of ReserveValue and ReserveGroup is False.
 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

Cuervo, et al. Standards Track [Page 25] RFC 2885 Megaco Protocol August 2000

 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 (RFC2327).  In session descriptions
 sent from the MGC to the MG, the following exceptions to the syntax
 of RFC 2327 are allowed:
  .  the "s=", "t=" and "o=" lines are optional,
  .  the use of CHOOSE is allowed in place of a single parameter
     value, and
  .  the use of alternatives is allowed in place of a single parameter
     value.
 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
 RFC2327. 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.
 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
  .  unspecified (i.e., absent),
  .  empty,
  .  underspecified through use of CHOOSE in a property value,
  .  fully specified, or
  .  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 section 7.1.1, with
 the following additional comments for clarification:

Cuervo, et al. Standards Track [Page 26] RFC 2885 Megaco Protocol August 2000

 (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.
 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.
  .  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.

Cuervo, et al. Standards Track [Page 27] RFC 2885 Megaco Protocol August 2000

  .  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.
  .  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.
  .  If the Mode property of the LocalControl descriptor is RecvOnly
     or SendRecv, 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:
  .  The MG chooses the first alternative in Local for which it is
     able to support at least one alternative in Remote.
  .  If the MG is unable to support at least one Local and one Remote
     alternative, it returns Error 510 (Insufficient Resources).
  .  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.

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 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.
 The default action of the MG, when it detects an event in the Events
 Descriptor, is to send a Notify command to the MG.  Any other action
 is for further study.
 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 that an embedded EventsDescriptor being activated, the MG
 continues event processing based on the newly activated
 EventsDescriptor (Note -  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 = 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.

Cuervo, et al. Standards Track [Page 29] RFC 2885 Megaco Protocol August 2000

 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 default action of the MG is to send a
       Notify command to the MGC and remove the event from the
       EventBuffer.  Any other action is for further study.  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 matching the
       EventsBufferDescriptor will be placed in  the EventBuffer and
       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 for specific transport considerations.
 The default value of EventBufferControl is Off.
 Note -  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, detection 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 detected.  It is
 possible, for example, to specify that the dial-tone Signal be

Cuervo, et al. Standards Track [Page 30] RFC 2885 Megaco Protocol August 2000

 generated when an off-hook Event is detected, or that the dial-tone
 Signal be stopped when a digit is detected.  A media gateway
 controller shall not send EventsDescriptors with an event both marked
 KeepActive and containing an embedded SignalsDescriptor.
 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.

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

 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
 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.  When the MGC enables the signal completion event
 (see section E.1.2) in an Events Descriptor, that event is detected
 whenever a signal terminates and "notifyCompletion" for that signal
 is set to TRUE.  The signal completion event of section E.1.2 has a
 parameter that indicates how the signal terminated: it played to

Cuervo, et al. Standards Track [Page 31] RFC 2885 Megaco Protocol August 2000

 completion, it was interrupted by an event, it was halted because a
 new SignalsDescriptor arrived, or the signal did not complete for
 some other reason.
 The duration is an integer value that is expressed in hundredths of a
 second.
 There are three types of signals:
  .  on/off - the signal lasts until it is turned off,
  .  timeout - the signal lasts until it is turned off or a specific
     period of time elapses,
  .  brief - the signal duration is so short that it will stop on its
     own unless a new signal is applied that causes it to stop; no
     timeout value is needed.
 If the signal type is specified in a SignalsDescriptor, it overrides
 the default signal type (see Section 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, a
 sequence of signals to be played sequentially, and a signal type.
 Only the trailing element of the sequence of signals in a sequential
 signal list may be an on/off signal.  If the trailing element of the
 sequence is an on/off signal, the signal type of the sequential
 signal list shall be on/off as well.  If the sequence of signals in a
 sequential signal list contains signals of type timeout and the
 trailing element is not of type on/off, the type of the sequential
 signal list SHALL be set to timeout.  The duration of a sequential
 signal list with type timeout is the sum of the durations of the
 signals it contains.  If the sequence of signals in a sequential
 signal list contains only signals of type brief, the type of the
 sequential signal list SHALL be set to brief.  A signal list is
 treated as a single signal of the specified type when played out.
 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.
 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 section 7.1.9).

Cuervo, et al. Standards Track [Page 32] RFC 2885 Megaco Protocol August 2000

 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 flagshall 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
  .  the signal type and sequence of signals in the sequential signal
     list in the replacement descriptor shall be ignored, and
  .  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 a
 descriptor even if the descriptor in the command was not present, or
 had no underspecified parameters.  Possible items in the Audit
 Descriptor are:
       Modem
       Mux
       Events
       Media
       Signals
       ObservedEvents
       DigitMap
       Statistics
       Packages
       EventBuffer
 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

Cuervo, et al. Standards Track [Page 33] RFC 2885 Megaco Protocol August 2000

  . ServiceChangeDelay
  . ServiceChangeProfile
  . ServiceChangeVersion
  . ServiceChangeMGCId
  . TimeStamp
 See section 7.2.8.

7.1.14 DigitMap Descriptor

 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:
  .  A new DigitMap is created by specifying a name that is not yet
     defined.  The value shall be present.
  .  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.
  .  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.
 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).

Cuervo, et al. Standards Track [Page 34] RFC 2885 Megaco Protocol August 2000

 1. The start timer (T) is used prior to any digits having been
    dialed.
 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.  The Start
 timer is started at the beginning of every digit map use, but can be
 overridden.
 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
 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 the 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"

Cuervo, et al. Standards Track [Page 35] RFC 2885 Megaco Protocol August 2000

 and "L" respectively indicate that the MG should use the short (S)
 timer or the long (L) timer for subsequent events, over-riding the
 timing rules described above. A timer specifier following a dot
 specifies inter-event timing for all events matching the dot as well
 as for subsequent events.  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 results are
 undefined.
 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.
 A digit map is active while the events descriptor which invoked it is
 active and it has not completed.  A digit map completes when:
  .  a timer has expired, or
  .  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
  .  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.
 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

Cuervo, et al. Standards Track [Page 36] RFC 2885 Megaco Protocol August 2000

    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 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, 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 (because the
    candidate set still contains more than one alternative event
    sequence), processing returns to step 2.
 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 which
 itself contains a digit map parameter.  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

Cuervo, et al. Standards Track [Page 37] RFC 2885 Megaco Protocol August 2000

 string from an earlier activation are lost.  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 the events in the package containing the
 specified digit map completion event other than the completion event
 itself are not individually notified.
 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 if the event
 includes a digit map parameter.  Regardless of whether a digit map is
 activated, this form of event specification will cause the individual
 events to be reported to the MGC as they are detected.
 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 Annex E (section E.6) is
 used to collect the dialled digits, then the dialling 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 parameter 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
 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 behavior 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.

Cuervo, et al. Standards Track [Page 38] RFC 2885 Megaco Protocol August 2000

 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 and the detection time(s).  Detection times are reported
 with a precision of hundredths of a second.  Time is expressed in
 UTC.

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
 sections, 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.
 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.
 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.
  .  (T1, T2, isolate) means that the Terminations matching T2 do not
     receive media from the Terminations matching T1, nor vice versa.
  .  (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.
  .  (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

Cuervo, et al. Standards Track [Page 39] RFC 2885 Megaco Protocol August 2000

     Terminations that match both T1 and T2.  However, if there is a
     Termination that matches both, no loopback is introduced;
     loopbacks are created by setting the TerminationMode.  CHOOSE
     wildcards may be used in T1 and T2 as well, under the following
     restrictions:
  .  the action (see section 8) of which the topology descriptor is
     part contains an Add command in which a CHOOSE wildcard is used;
  .  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. The default association when a termination is not
 mentioned in the Topology descriptor is bothway (if T3 is added to a
 context with T1 and T2 with topology (T3,T1,oneway) it will be
 connected bothway to T2).

Cuervo, et al. Standards Track [Page 40] RFC 2885 Megaco Protocol August 2000

 The figure below 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.
          Context 1           Context 2           Context 3
    +------------------+  +------------------+  +------------------+
    |      +----+      |  |      +----+      |  |      +----+      |
    |      | T2 |      |  |      | T2 |      |  |      | T2 |      |
    |      +----+      |  |      +----+      |  |      +----+      |
    |       ^  ^       |  |          ^       |  |          ^       |
    |       |  |       |  |          |       |  |          |       |
    |    +--+  +--+    |  |          +---+   |  |          +--+    |
    |    |        |    |  |              |   |  |             |    |
    |    v        v    |  |              v   |  |             |    |
    | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
    | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |  | | T1 |<-->| T3 | |
    | +----+    +----+ |  | +----+    +----+ |  | +----+    +----+ |
    +------------------+  +------------------+  +------------------+
     1. No Topology Desc.  2. T1, T2 Isolate     3. T3, T2 oneway
          Context 1           Context 2           Context 3
    +------------------+  +------------------+  +------------------+
    |      +----+      |  |      +----+      |  |      +----+      |
    |      | 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
            Figure 4: A Sequence Of Example Topologies

Cuervo, et al. Standards Track [Page 41] RFC 2885 Megaco Protocol August 2000

            Topology                Description
                1             No topology descriptors
         When no topology descriptors are included, all
         terminations have a both way connection to all
         other terminations.
                2                 T1, T2, Isolate
         Removes the connection between T1 and T2.
           T3 has a both way connection with both T1 and
           T2.  T1 and T2 have bothway connection to T3.
                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 bothway
                        and T1,T3 bothway may be implied
                        or explicit).
         All terminations have a bothway connection to
         all other terminations.
 A oneway connection must implemented in such a way that the other
 Terminations in the Context are not aware of the change in topology.

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
 specified in later subsections.  All parameters enclosed by square
 brackets ([. . . ]) are considered optional.

Cuervo, et al. Standards Track [Page 42] RFC 2885 Megaco Protocol August 2000

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]
      [, 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.  For an existing Termination, the TerminationID would be
 specific.  For a Termination that does not yet exist, the
 TerminationID is specified as CHOOSE  in the command. The new
 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.
 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.

Cuervo, et al. Standards Track [Page 43] RFC 2885 Megaco Protocol August 2000

 The EventsDescriptor parameter is optional.  If present, it provides
 the list of events that should be detected on the Termination.
 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, 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]
      Modify( TerminationID
      [, MediaDescriptor]
      [, ModemDescriptor]
      [, MuxDescriptor]
      [, EventsDescriptor]
      [, 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

Cuervo, et al. Standards Track [Page 44] RFC 2885 Megaco Protocol August 2000

 TerminationIDs match is not specified. The CHOOSE option is an error,
 as the Modify command may only be used on existing Terminations.
 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]
 [,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
 CHOOSE option 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.
 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
 descriptors as specified in the AuditDescriptor.   Possible return
 values are the same as those to Add.

Cuervo, et al. Standards Track [Page 45] RFC 2885 Megaco Protocol August 2000

 When a provisioned Termination is Subtracted from a context, its
 property values shall revert to:
  .  the default value, if specified for the property and not
     overridden by provisioning,
  .  otherwise, the provisioned value.

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]
      [, SignalsDescriptor]
      [, DigitMapDescriptor]
      [, AuditDescriptor]
      )
 The TerminationID specifies the Termination to be moved.  It may be
 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. By convention, the Termination is subtracted from its
 previous Context. 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.

Cuervo, et al. Standards Track [Page 46] RFC 2885 Megaco Protocol August 2000

 The remaining descriptors are processed as in the Modify 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.
 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,
 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

Cuervo, et al. Standards Track [Page 47] RFC 2885 Megaco Protocol August 2000

 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.
 AuditValue results depend on the Context, viz. specific, null, or
 wildcarded.  The TerminationID may be specific, or wildcarded.  The
 following illustrates other information that can be obtained with the
 Audit 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

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]

Cuervo, et al. Standards Track [Page 48] RFC 2885 Megaco Protocol August 2000

 [,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.  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.

7.2.7 Notify

 The Notify Command allows the Media Gateway to notify the Media
 Gateway Controller of events occurring within the Media Gateway.
      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 an indication of the time that the
 event was detected.  Procedures for sending Notify commands with
 RequestID equal to 0 are for further study.

Cuervo, et al. Standards Track [Page 49] RFC 2885 Megaco Protocol August 2000

 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.
 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).

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:
  .  ServiceChangeMethod
  .  ServiceChangeReason
  .  ServiceChangeDelay
  .  ServiceChangeAddress
  .  ServiceChangeProfile
  .  ServiceChangeVersion
  .  ServiceChangeMgcId
  .  TimeStamp
 The ServiceChangeMethod parameter specifies the type of ServiceChange
 that will or has occurred:

Cuervo, et al. Standards Track [Page 50] RFC 2885 Megaco Protocol August 2000

 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. 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 were lost. 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".
 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.  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.
 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 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

Cuervo, et al. Standards Track [Page 51] RFC 2885 Megaco Protocol August 2000

 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.
 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
 section 11.3).
 The optional TimeStamp parameter specifies the actual time as kept by
 the sender.  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, and is expressed in
 UTC.
 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 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.  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 section 9, transaction replies and pending

Cuervo, et al. Standards Track [Page 52] RFC 2885 Megaco Protocol August 2000

 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 an 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 Gateway specified in an
 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:
  .  ServiceChangeAddress, if the responding MGC wishes to specify an
     new destination for messages from the MG for the remainder of the
     association;
  .  ServiceChangeMgcId, if the responding MGC does not wish to
     sustain an association with the MG;
  .  ServiceChangeProfile, if the responder wishes to negotiate the
     profile to be used for the association;
  .  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 section 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

Cuervo, et al. Standards Track [Page 53] RFC 2885 Megaco Protocol August 2000

      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 sections
 apply to terminations.  This section specifies how contexts are
 manipulated and audited.
 Commands are grouped into actions (see section 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.
 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 RFC2234 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
 section 7.1.8.

Cuervo, et al. Standards Track [Page 54] RFC 2885 Megaco Protocol August 2000

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.
 The identified error codes are:
      400 - Bad Request
      401 - Protocol Error
      402 - Unauthorized
      403 - Syntax Error in Transaction
      404 - Syntax Error in TransactionReply
      405 - Syntax Error in TransactionPending
      406 - Version Not Supported
      410 - Incorrect identifier
      411 - The transaction refers to an unknown ContextId
      412 - No ContextIDs available
      421 - Unknown action or illegal combination of actions
      422 - Syntax Error in Action
      430 - Unknown TerminationID
      431 - No TerminationID matched a wildcard
      432 - Out of TerminationIDs or No TerminationID available
      433 - TerminationID is already in a Context
      440 - Unsupported or unknown Package
      441 - Missing RemoteDescriptor
      442 - Syntax Error in Command
      443 - Unsupported or Unknown Command
      444 - Unsupported or Unknown Descriptor
      445 - Unsupported or Unknown Property
      446 - Unsupported or Unknown Parameter
      447 - Descriptor not legal in this command
      448 - Descriptor appears twice in a command
      450 - No such property in this package
      451 - No such event in this package
      452 - No such signal in this package
      453 - No such statistic in this package
      454 - No such parameter value in this package
      455 - Parameter illegal in this Descriptor
      456 - Parameter or Property appears twice in this Descriptor
      461 - TransactionIDs in Reply do not match Request

Cuervo, et al. Standards Track [Page 55] RFC 2885 Megaco Protocol August 2000

      462 - Commands in Transaction Reply do not match commands in
            request
      463 - TerminationID of Transaction Reply does not match
            request
      464 - Missing reply in Transaction Reply
      465 - TransactionID in Transaction Pending does not match any
            open request
      466 - Illegal Duplicate Transaction Request
      467 - Illegal Duplicate Transaction Reply
      471 - Implied Add for Multiplex failure
      500 - Internal Gateway Error
      501 - Not Implemented
      502 - Not ready.
      503 - Service Unavailable
      504 - Command Received from unauthorized entity
      505 - Command Received before Restart Response
      510 - Insufficient resources
      512 - Media Gateway unequipped to detect requested Event
      513 - Media Gateway unequipped to generate requested Signals
      514 - Media Gateway cannot send the specified announcement
      515 - Unsupported Media Type
      517 - Unsupported or invalid mode
      518 - Event buffer full
      519 - Out of space to store digit map
      520 - Media Gateway does not have a digit map
      521 - Termination is "ServiceChangeing"
      526 - Insufficient bandwidth
      529 - Internal hardware failure
      530 - Temporary Network failure
      531 - Permanent Network failure
      581 - Does Not Exist

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 series of Commands 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.
 Following is a graphic representation of the Transaction, Action and
 Command relationships.

Cuervo, et al. Standards Track [Page 56] RFC 2885 Megaco Protocol August 2000

     +----------------------------------------------------------+
     | 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 5 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
 section 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.  Commands may be
 marked as "Optional" which can override this behaviour -  if a

Cuervo, et al. Standards Track [Page 57] RFC 2885 Megaco Protocol August 2000

 command marked as Optional results in an error, subsequent commands
 in the Transaction will be executed.  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.

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 shall not use partially specified ContextIDs
 containing the CHOOSE wildcard.
 The MGC may use the ALL wildcard to address all Contexts on the MG.

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 subsections.

Cuervo, et al. Standards Track [Page 58] RFC 2885 Megaco Protocol August 2000

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 the
 "Command Details" subsection titled "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.
      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 or null.
 Each of the Response parameters represents a return value as
 mentioned in section 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.

Cuervo, et al. Standards Track [Page 59] RFC 2885 Megaco Protocol August 2000

 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.
 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 Actions 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
 Transaction).
 If the end of a transaction can not 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 Transaction 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 Transaction 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

Cuervo, et al. Standards Track [Page 60] RFC 2885 Megaco Protocol August 2000

 by the MGC to indicate the interval within which the MG should
 expects a response to any transaction from the MGC.  Senders may
 receive more than one TransactionPending for a command.  If a
 duplicate request is received when pending, the responder may send a
 duplicate pending immediately, or continue waiting for its timer to
 trigger another Transaction Pending.

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.
 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.

9. TRANSPORT

 The transport mechanism for the protocol should allow the reliable
 transport of transactions between an 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 normative
 Annexes to this document.  Additional Transports may be defined as
 additional annexes in subsequent editions of this document, or in
 separate documents.  For transport of the protocol over IP, MGCs
 shall implement both TCP and UDP/ALF, an 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 section
 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, 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 section
 7.2.8, either the MG or the MGC may supply an address in the

Cuervo, et al. Standards Track [Page 61] RFC 2885 Megaco Protocol August 2000

 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.

9.1 Ordering of Commands

 This document 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:
  .  Notify commands may be delayed and arrive at the MGC after the
     transmission of a new command changing the EventsDescriptor
  .  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
 section 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.
 3. On a given Termination, there should normally be 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

Cuervo, et al. Standards Track [Page 62] RFC 2885 Megaco Protocol August 2000

    commands for Terminations named by the wild-carding (or implied in
    a Multiplex descriptor) should not be sent until the wild-carded
    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 behavior 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.
 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

Cuervo, et al. Standards Track [Page 63] RFC 2885 Megaco Protocol August 2000

 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 section 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 document for setting
 up unauthorized calls or interfering with authorized calls.  The
 security mechanism for the protocol when transported over IP networks
 is IPsec [RFC2401 to RFC2411].
 The AH header [RFC2402] affords data origin authentication,
 connectionless integrity and optional anti-replay protection of
 messages passed between the MG and the MGC. The ESP header [RFC2406]
 provides confidentiality of messages, if desired. For 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 document employing
 the ESP header SHALL comply with section 5 of [RFC2406], which
 defines a minimum set of algorithms for integrity checking and

Cuervo, et al. Standards Track [Page 64] RFC 2885 Megaco Protocol August 2000

 encryption. Similarly, implementations employing the AH header SHALL
 comply with section 5 of [RFC2402], which defines a minimum set of
 algorithms for integrity checking using manual keys.
 Implementations SHOULD use IKE [RFC2409] 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 document where the
 underlying network implementation does not support IPsec.
 As an interim solution, an optional AH header is defined within the
 H.248 protocol header. The header fields are exactly those of the
 SPI, SEQUENCE NUMBER and DATA fields as defined in [RFC2402]. The
 semantics of the header fields are the same as the "transport mode"
 of [RFC2402], 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 the entire transaction prepended by a synthesized IP
 header consisting of a 32 bit source IP address, a 32 bit destination
 address and an 16 bit UDP encoded as 10 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 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.
 All implementations of the interim AH mechanism SHALL comply with
 section 5 of [RFC2402] 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

Cuervo, et al. Standards Track [Page 65] RFC 2885 Megaco Protocol August 2000

 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:
  .  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 roundtrip, 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
     roundtrip and settle for slower call-set-up procedures.
  .  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.
 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

Cuervo, et al. Standards Track [Page 66] RFC 2885 Megaco Protocol August 2000

 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
 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.

Cuervo, et al. Standards Track [Page 67] RFC 2885 Megaco Protocol August 2000

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 will
 send a Transaction Accept, with the ServiceChangeMgcId set to itself.
 If the MG receives an ServiceChangeMgcId not equal to the MGC it
 contacted, 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 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.
 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 Restart Response.

11.3 Negotiation of Protocol Version

 The first ServiceChange command from an 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
 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.

Cuervo, et al. Standards Track [Page 68] RFC 2885 Megaco Protocol August 2000

 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, descriptor, property,
    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 an 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
 "Failover" method and a "MG Impending Failure" reason.  The MGC then
 uses the primary MG as the active MG.  When the error condition is
 repaired, the Working MG can send a "ServiceChange" with a "Restart"
 method.

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.
 In partial failure, or 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

Cuervo, et al. Standards Track [Page 69] RFC 2885 Megaco Protocol August 2000

 designated replacement in ServiceChangeMgcId. The MG should 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, or
 fails to see an Audit command subsequently, it should behave as if
 its MGC failed, and start contacting secondary MGCs.  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 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 recommendation. 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, transaction replies are sent to the new MGC (after
 a new control association is established), and the MG should expect
 outstanding transaction replies from the new MGC.  No new messages
 shall be sent to the new 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 annexes).

Cuervo, et al. Standards Track [Page 70] RFC 2885 Megaco Protocol August 2000

 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 section 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.
 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.
  .  Extends (Optional): 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

Cuervo, et al. Standards Track [Page 71] RFC 2885 Megaco Protocol August 2000

     existing parameter described in the original package. An extended
     package shall not redefine or overload a name defined in the
     original package.  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.

12.1.2 Properties

 Properties defined by the package, specifying:
  .  Property Name: only descriptive.
  .  PropertyID:  Is an identifier
  .  Description:
  .  Type: One of:
        String: UTF-8 string
        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
        Boolean
  .  Possible Values:
  .  Defined in: Which H.248 descriptor the property is defined in.
     LocalControl is for stream dependent properties. TerminationState
     is for stream independent properties.
  .  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
     section 12.2.

Cuervo, et al. Standards Track [Page 72] RFC 2885 Megaco Protocol August 2000

  .  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 section 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)
         - TO (TimeOut)
         - BR (Brief)
 Note -  SignalType may be defined such that it is dependent on the
 value of one or more parameters. Signals that would be played with
 SignalType BR should have a default duration. The package has to
 define the default duration and signalType.
  .  Duration: in hundredths of seconds
  .  Additional Parameters: See section 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 Properties, Statistics and Parameters to

   Events and Signals.
  . Parameter Name: only descriptive
  . ParameterID: Is an identifier
  . Type: One of:
       String: UTF-8 octet string
       Integer: 4 octet signed integer
       Double: 8 octet signed integer

Cuervo, et al. Standards Track [Page 73] RFC 2885 Megaco Protocol August 2000

       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
       Boolean
  . Possible values:
  . 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 alphanumeric character and
 consisting of alphanumeric characters and / or digits, and possibly
 including the special character underscore ("_").
 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 section 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 60000-64565 are reserved for private use. Serial
    number 0 is reserved.

Cuervo, et al. Standards Track [Page 74] RFC 2885 Megaco Protocol August 2000

 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

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.

Cuervo, et al. Standards Track [Page 75] RFC 2885 Megaco Protocol August 2000

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.

Cuervo, et al. Standards Track [Page 76] RFC 2885 Megaco Protocol August 2000

ANNEX A: BINARY ENCODING OF THE PROTOCOL (NORMATIVE)

 This Annex specifies the syntax of messages using the notation
 defined in ASN.1 [ITU-T Recommendation X.680 (1997): 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 [ITU-T Recommendation
 X.690(1994) Information Technology - ASN.1 Encoding Rules:
 Specification of Basic Encoding Rules (BER)].

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 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 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 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.
 Addressing ALL names with prefix 00000001 00011110 is done as
 follows:
      wildcarding field: 10000111
      Termination ID: 00000001 00011110 xxxxxxxx.

Cuervo, et al. Standards Track [Page 77] RFC 2885 Megaco Protocol August 2000

 The values of the bits labeled "x" is irrelevant and shall be ignored
 by the receiver.
 Indicating to the receiver that is 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.

A.2 ASN.1 syntax specification

 This section contains the ASN.1 specification of the H.248 protocol
 syntax.
 NOTE -  In case a transport mechanism is used that employs
 application level framing, the definition of Transaction below
 changes.  Refer to the annex defining the transport mechanism for the
 definition that applies in that case.
 NOTE - The ASN.1 specification below contains a clause defining
 TerminationIDList as a sequence of TerminationIDs.  The length of
 this sequence SHALL be one.  The SEQUENCE OF construct is present
 only to allow future extensions.
 MEDIA-GATEWAY-CONTROL DEFINITIONS AUTOMATIC TAGS::= BEGIN

Cuervo, et al. Standards Track [Page 78] RFC 2885 Megaco Protocol August 2000

 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 (16..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,
              transactions    SEQUENCE OF Transaction
      },
      ...
 }
 MId ::= CHOICE
 {
      ip4Address                      IP4Address,
      ip6Address                      IP6Address,
      domainName                      DomainName,
      deviceName                      PathName,
      mtpAddress                      OCTET STRING(SIZE(2)),
  -- Addressing structure of mtpAddress:
  --        15                0
  --        |  PC        | NI |
  --           14 bits    2 bits
       ...
 }
 DomainName ::= SEQUENCE
 {

Cuervo, et al. Standards Track [Page 79] RFC 2885 Megaco Protocol August 2000

      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 section A.3
 Transaction ::= CHOICE
 {
      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,
      ...
 }

Cuervo, et al. Standards Track [Page 80] RFC 2885 Megaco Protocol August 2000

 TransactionReply ::= SEQUENCE
 {
      transactionId           TransactionId,
      transactionResult       CHOICE
      {
           transactionError   ErrorDescriptor,
           actionReplies      SEQUENCE OF ActionReply
      },
      ...
 }
 TransactionResponseAck ::= SEQUENCE
 {
      firstAck        TransactionId,
      lastAck         TransactionId OPTIONAL
 }
 ErrorDescriptor ::= SEQUENCE
 {
      errorCode       ErrorCode,
      errorText       ErrorText OPTIONAL
 }
 ErrorCode ::= INTEGER(0..65535)
 -- See section 13 for IANA considerations w.r.t. error codes
 ErrorText ::= IA5String
 ContextID ::= INTEGER(0..4294967295)
  1. - Context NULL Value: 0
  2. - Context CHOOSE Value: 429467294 (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,

Cuervo, et al. Standards Track [Page 81] RFC 2885 Megaco Protocol August 2000

      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,
      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

Cuervo, et al. Standards Track [Page 82] RFC 2885 Megaco Protocol August 2000

      auditCapReply           AuditReply,
      auditValueReply         AuditReply,
      notifyReply             NotifyReply,
      serviceChangeReply      ServiceChangeReply,
      ...
 }
 TopologyRequest ::= SEQUENCE
 {
      terminationFrom         TerminationID,
      terminationTo           TerminationID,
      topologyDirection       ENUMERATED
      {
              bothway(0),
              isolate(1),
              oneway(2)
      }
 }
 AmmRequest ::= SEQUENCE
 {
      terminationID           TerminationIDList,
      mediaDescriptor         MediaDescriptor OPTIONAL,
      modemDescriptor         ModemDescriptor OPTIONAL,
      muxDescriptor           MuxDescriptor OPTIONAL,
      eventsDescriptor        EventsDescriptor OPTIONAL,
      eventBufferDescriptor   EventBufferDescriptor OPTIONAL,
      signalsDescriptor       SignalsDescriptor OPTIONAL,
      digitMapDescriptor      DigitMapDescriptor OPTIONAL,
      auditDescriptor         AuditDescriptor OPTIONAL,
      ...
 }
 AmmsReply ::= SEQUENCE
 {
      terminationID           TerminationIDList,
      terminationAudit        TerminationAudit OPTIONAL
 }
 SubtractRequest ::= SEQUENCE
 {
      terminationID           TerminationIDList,
      auditDescriptor         AuditDescriptor OPTIONAL,
      ...
 }
 AuditRequest ::= SEQUENCE
 {

Cuervo, et al. Standards Track [Page 83] RFC 2885 Megaco Protocol August 2000

      terminationID           TerminationID,
      auditDescriptor         AuditDescriptor,
      ...
 }
 AuditReply ::= SEQUENCE
 {
      terminationID           TerminationID,
      auditResult             AuditResult
 }
 AuditResult ::= CHOICE
 {
      contextAuditResult      TerminationIDList,
      terminationAuditResult  TerminationAudit
 }
 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,
      ...
 }
 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,
      ...
 }

Cuervo, et al. Standards Track [Page 84] RFC 2885 Megaco Protocol August 2000

 NotifyRequest ::= SEQUENCE
 {
      terminationID                   TerminationIDList,
      observedEventsDescriptor        ObservedEventsDescriptor,
      errorDescriptor                 ErrorDescriptor OPTIONAL,
      ...
 }
 NotifyReply ::= SEQUENCE
 {
      terminationID                   TerminationIDList OPTIONAL,
      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
 }
 ServiceChangeRequest ::= SEQUENCE
 {
      terminationID                   TerminationIDList,
      serviceChangeParms              ServiceChangeParm,
      ...
 }
 ServiceChangeReply ::= SEQUENCE
 {
      terminationID                   TerminationIDList,
      serviceChangeResult             ServiceChangeResult,

Cuervo, et al. Standards Track [Page 85] RFC 2885 Megaco Protocol August 2000

      ...
 }
  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 Section 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
              },
      ...
 }
 StreamDescriptor ::= SEQUENCE
 {
      streamID                        StreamID,
      streamParms                     StreamParms
 }
 StreamParms ::= SEQUENCE
 {
      localControlDescriptor     LocalControlDescriptor OPTIONAL,
      localDescriptor            LocalRemoteDescriptor OPTIONAL,
      remoteDescriptor           LocalRemoteDescriptor OPTIONAL,
      ...
 }

Cuervo, et al. Standards Track [Page 86] RFC 2885 Megaco Protocol August 2000

 LocalControlDescriptor ::= SEQUENCE
 {
      streamMode      StreamMode OPTIONAL,
      reserveValue    BOOLEAN,
      reserveGroup    BOOLEAN,
      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. - longer sequence means "choose one of the values"
  6. - The relation field may only be selected if the value sequence
  7. - has length 1. It indicates that the MG has to choose a value
  8. - for the property. E.g., x > 3 (using the greaterThan
  9. - value for relation) instructs the MG to choose any value larger
  10. - than 3 for property x.
  11. - The range field may only be selected if the value sequence
  12. - has length 2. It indicates that the MG has to choose a value
  13. - in the range between the first octet in the value sequence and
  14. - the trailing octet in the value sequence, including the
  15. - boundary values.
  16. - When sent by the MG, only responses to an AuditCapability request
  17. - may contain multiple values, a range, or a relation field.
 PropertyParm ::= SEQUENCE
 {
      name            PkgdName,
      value           SEQUENCE OF OCTET STRING,
      extraInfo       CHOICE
              {
                      relation        Relation,
                      range           BOOLEAN
              } OPTIONAL
 }

Cuervo, et al. Standards Track [Page 87] RFC 2885 Megaco Protocol August 2000

 Name ::= OCTET STRING(SIZE(2))
 PkgdName ::= OCTET STRING(SIZE(4))
 -- represents Package Name (2 octets) plus Property Name (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.
 -- Wildcarding of Package Name is permitted only if Property Name is
 -- 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,
      ...
 }
 EventBufferControl ::= ENUMERATED
 {
      Off(0),
      LockStep(1),
      ...
 }
 ServiceState ::= ENUMERATED
 {
      test(0),
      outOfSvc(1),
      inSvc(2),
       ...
 }

Cuervo, et al. Standards Track [Page 88] RFC 2885 Megaco Protocol August 2000

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

Cuervo, et al. Standards Track [Page 89] RFC 2885 Megaco Protocol August 2000

 SecondEventsDescriptor ::= SEQUENCE
 {
      requestID               RequestID,
      eventList               SEQUENCE OF SecondRequestedEvent
 }
 SecondRequestedEvent ::= SEQUENCE
 {
      pkgdName                PkgdName,
      streamID                StreamID OPTIONAL,
      eventAction             SecondRequestedActions OPTIONAL,
      evParList               SEQUENCE OF EventParameter
 }
 SecondRequestedActions ::= SEQUENCE
 {
      keepActive              BOOLEAN,
      eventDM                 EventDM OPTIONAL,
      signalsDescriptor       SignalsDescriptor OPTIONAL,
      ...
 }
 EventBufferDescriptor ::= SEQUENCE OF ObservedEvent
 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        BOOLEAN OPTIONAL,
      keepActive              BOOLEAN OPTIONAL,
      sigParList              SEQUENCE OF SigParameter
 }

Cuervo, et al. Standards Track [Page 90] RFC 2885 Megaco Protocol August 2000

 SignalType ::= ENUMERATED
 {
      brief(0),
      onOff(1),
      timeOut(2),
      ...
 }
 SignalName ::= PkgdName
 SigParameter ::= SEQUENCE
 {
      sigParameterName                Name,
      value                           Value
 }
 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,
      digitMapValue           DigitMapValue
 }
 DigitMapName ::= Name
 DigitMapValue ::= SEQUENCE

Cuervo, et al. Standards Track [Page 91] RFC 2885 Megaco Protocol August 2000

 {
      startTimer              INTEGER(0..99) OPTIONAL,
      shortTimer              INTEGER(0..99) OPTIONAL,
      longTimer               INTEGER(0..99) OPTIONAL,
      digitMapBody            IA5String
      -- See Section 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,
      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)),
      ...
 }
 ServiceChangeResParm ::= SEQUENCE
 {
      serviceChangeMgcId      MId OPTIONAL,
      serviceChangeAddress    ServiceChangeAddress OPTIONAL,
      serviceChangeVersion    INTEGER(0..99) OPTIONAL,
      serviceChangeProfile    ServiceChangeProfile OPTIONAL
 }
 ServiceChangeMethod ::= ENUMERATED
 {
      failover(0),
      forced(1),
      graceful(2),
      restart(3),
      disconnected(4),

Cuervo, et al. Standards Track [Page 92] RFC 2885 Megaco Protocol August 2000

      handOff(5),
      ...
 }
 ServiceChangeProfile ::= SEQUENCE
 {
      profileName     Name,
      version         INTEGER(0..99)
 }
 PackagesDescriptor ::= SEQUENCE OF PackagesItem
 PackagesItem ::= SEQUENCE
 {
      packageName             Name,
      packageVersion  INTEGER(0..99)
 }
 StatisticsDescriptor ::= SEQUENCE OF StatisticsParameter
 StatisticsParameter ::= SEQUENCE
 {
      statName                PkgdName,
      statValue               Value
 }
 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
 {    t35CountryCode     INTEGER(0..255), -- country, as per T.35
      t35Extension       INTEGER(0..255), -- assigned nationally
      manufacturerCode   INTEGER(0..65535), -- assigned nationally
      ...
 }

Cuervo, et al. Standards Track [Page 93] RFC 2885 Megaco Protocol August 2000

 TimeNotation ::= SEQUENCE
 {
      date            IA5String(SIZE(8)),  -- yyyymmdd format
      time            IA5String(SIZE(8))  -- hhmmssss format
 }
 Value ::= OCTET STRING
 END

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 section 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
 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

Cuervo, et al. Standards Track [Page 94] RFC 2885 Megaco Protocol August 2000

 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.
 PathName = NAME *(["/"] ["*"] ["@"] (ALPHA / DIGIT)) ["*"]
 NAME = ALPHA *63(ALPHA / DIGIT / "_" )

ANNEX B TEXT ENCODING OF THE PROTOCOL (NORMATIVE)

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 RFC2234.
 megacoMessage        = LWSP [authenticationHeader SEP ] message
 authenticationHeader = AuthToken EQUAL SecurityParmIndex COLON
                        SequenceNum COLON AuthData
 SecurityParmIndex    = "0x" 8(HEXDIG)
 SequenceNum          = "0x" 8(HEXDIG)
 AuthData             = "0x" 32*64(HEXDIG)
 message    = MegacopToken SLASH Version SEP mId SEP messageBody
 ; The version of the protocol defined here is equal to 1.
 messageBody          = ( errorDescriptor / transactionList )
 transactionList      = 1*( transactionRequest / transactionReply /
                        transactionPending / transactionResponseAck )
 ;Use of response acks is dependent on underlying transport
 transactionPending   = PendingToken EQUAL TransactionID LBRKT RBRKT

Cuervo, et al. Standards Track [Page 95] RFC 2885 Megaco Protocol August 2000

 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 )
 commandRequestList= ["O-"] commandRequest *(COMMA ["O-"]
 commandRequest)
 commandRequest     = ( ammRequest / subtractRequest / auditRequest
                         / notifyRequest / serviceChangeRequest)
 transactionReply     = ReplyToken EQUAL TransactionID LBRKT
                        ( errorDescriptor / actionReplyList ) RBRKT
 actionReplyList      = actionReply *(COMMA actionReply )
 actionReply          = CtxToken EQUAL ContextID LBRKT
                        ( errorDescriptor / commandReply ) RBRKT
 commandReply       = (( contextProperties [COMMA commandReplyList] )
                         / commandReplyList )
 commandReplyList     = commandReplys *(COMMA commandReplys )

Cuervo, et al. Standards Track [Page 96] RFC 2885 Megaco Protocol August 2000

 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      =  ["W-"] SubtractToken EQUAL TerminationID
                         [ LBRKT auditDescriptor RBRKT]
 auditRequest         = ["W-"] (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 )
 ;at-most-once except errorDescriptor
 auditReturnParameter = (mediaDescriptor / modemDescriptor /
                         muxDescriptor / eventsDescriptor /
                         signalsDescriptor / digitMapDescriptor /
                   observedEventsDescriptor / eventBufferDescriptor /
                         statisticsDescriptor / packagesDescriptor /
                          errorDescriptor )
 auditDescriptor      = AuditToken LBRKT [ auditItem
                        *(COMMA auditItem) ] RBRKT

Cuervo, et al. Standards Track [Page 97] RFC 2885 Megaco Protocol August 2000

 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
 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".."225"
 ; this production, while occurring in RFC2373, is not referenced
 ; IPv6prefix           = hexpart SLASH 1*2DIGIT
 hexpart          = hexseq "::" [ hexseq ] / "::" [ hexseq ] / hexseq
 hexseq               = hex4 *( ":" hex4)
 hex4                 = 1*4HEXDIG
 portNumber           = UINT16
 ; An mtp address is two octets long
 mtpAddress           = MTPToken LBRKT octetString RBRKT

Cuervo, et al. Standards Track [Page 98] RFC 2885 Megaco Protocol August 2000

 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-once per item
 ; and either streamParm or streamDescriptor but not both
 mediaParm            = (streamParm / streamDescriptor /
                         terminationStateDescriptor)
 ; at-most-once
 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
 localParm            = ( streamMode / propertyParm /
 reservedValueMode
      / reservedGroupMode )
 reservedValueMode       = ReservedValueToken EQUAL ( "ON" / "OFF" )
 reservedGroupMode       = ReservedGroupToken EQUAL ( "ON" / "OFF" )
 streamMode           = ModeToken EQUAL streamModes
 streamModes          = (SendonlyToken / RecvonlyToken /
 SendrecvToken /
                        InactiveToken / LoopbackToken )

Cuervo, et al. Standards Track [Page 99] RFC 2885 Megaco Protocol August 2000

 propertyParm         = pkgdName parmValue
 parmValue            = (EQUAL alternativeValue/ INEQUAL VALUE)
 alternativeValue     = ( VALUE / LSBRKT VALUE *(COMMA VALUE) RSBRKT
 /
                        LSBRKT VALUE DOT DOT VALUE RSBRKT )
 INEQUAL              = LWSP (">" / "<" / "#" ) LWSP
 LSBRKT               = LWSP "[" LWSP
 RSBRKT               = LWSP "]" LWSP
 localDescriptor      = LocalToken LBRKT octetString RBRKT
 remoteDescriptor     = RemoteToken LBRKT octetString RBRKT
 eventBufferDescriptor= EventBufferToken LBRKT observedEvent
                        *( COMMA observedEvent ) RBRKT
 eventBufferControl     = BufferToken EQUAL ( "OFF" / LockStepToken )
 terminationStateDescriptor = TerminationStateToken LBRKT
             terminationStateParm *( COMMA terminationStateParm )
 RBRKT
 ; at-most-once per item
 terminationStateParm =(propertyParm / serviceStates /
 eventBufferControl )
 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 events in package
                  / ("*" SLASH "*") ; all events supported by the MG
 PackageName          = NAME
 ItemID               = NAME
 eventsDescriptor     = EventsToken EQUAL RequestID LBRKT
                       requestedEvent *( COMMA requestedEvent ) RBRKT
 requestedEvent       = pkgdName [ LBRKT eventParameter
                        *( COMMA eventParameter ) RBRKT ]

Cuervo, et al. Standards Track [Page 100] RFC 2885 Megaco Protocol August 2000

 ; 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
 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

Cuervo, et al. Standards Track [Page 101] RFC 2885 Megaco Protocol August 2000

 ;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 ("ON" / "OFF")
 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 ]
 ;at-most-once eventStream, every eventParameterName at most once
 observedEventParameter = eventStream / eventOther
 RequestID            = UINT32
 modemDescriptor      = ModemToken (( EQUAL modemType) /
                        (LSBRKT modemType *(COMMA modemType) RSBRKT))
                        [ LBRKT NAME parmValue
                       *(COMMA NAME parmValue) RBRKT ]
 ; at-most-once
 modemType            = (V32bisToken / V22bisToken / V18Token /
                         V22Token / V32Token / V34Token / V90Token /
                      V91Token / SynchISDNToken / extensionParameter)
 digitMapDescriptor   = DigitMapToken EQUAL digitMapName
                        ( LBRKT digitMapValue RBRKT )
 digitMapName       = NAME
 digitMapValue      = ["T" COLON Timer COMMA] ["S" COLON Timer COMMA]
                        ["L" COLON Timer COMMA] digitMap
 Timer              = 1*2DIGIT
 digitMap =
      digitString / LWSP "(" LWSP digitStringList LWSP ")" LWSP)

Cuervo, et al. Standards Track [Page 102] RFC 2885 Megaco Protocol August 2000

 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
 auditItem            = ( MuxToken / ModemToken / MediaToken /
                         SignalsToken / EventBufferToken /
                         DigitMapToken / StatsToken / EventsToken /
                         ObservedEventsToken / PackagesToken )
 serviceChangeDescriptor = ServicesToken LBRKT serviceChangeParm
                          *(COMMA serviceChangeParm) RBRKT
 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
 servChgReplyParm     = (serviceChangeAddress / serviceChangeMgcId /
                        serviceChangeProfile / serviceChangeVersion )
 serviceChangeMethod  = MethodToken EQUAL (FailoverToken /
                        ForcedToken / GracefulToken / RestartToken /
                        DisconnectedToken / HandOffToken /
                        extensionParameter)
 serviceChangeReason  = ReasonToken  EQUAL VALUE
 serviceChangeDelay   = DelayToken   EQUAL UINT32
 serviceChangeAddress = ServiceChangeAddressToken EQUAL VALUE
 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)

Cuervo, et al. Standards Track [Page 103] RFC 2885 Megaco Protocol August 2000

 packagesItem         = NAME "-" UINT16
 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 terminationA COMMA
                        terminationB COMMA topologyDirection RBRKT
 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 )
 quotedString         = DQUOTE 1*(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 ; ","
 DOT                  = %x2E           ; "."
 SLASH                = %x2F           ; "/"

Cuervo, et al. Standards Track [Page 104] RFC 2885 Megaco Protocol August 2000

 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             = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#"
 /
                        "<" / ">" / "="
 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")
 DiscardToken               = ("Discard"               / "DS")
 DisconnectedToken          = ("Disconnected"          / "DC")
 DelayToken                 = ("Delay"                 / "DL")
 DurationToken              = ("Duration"              / "DR")
 EmbedToken                 = ("Embed"                 / "EB")
 EmergencyToken             = ("Emergency"             / "EM")
 ErrorToken                 = ("Error"                 / "ER")
 EventBufferToken           = ("EventBuffer"           / "EB")
 EventsToken                = ("Events"                / "E")
 FailoverToken              = ("Failover"              / "FL")
 ForcedToken                = ("Forced"                / "FO")
 GracefulToken              = ("Graceful"              / "GR")
 H221Token                  = ("H221" )
 H223Token                  = ("H223" )
 H226Token                  = ("H226" )
 HandOffToken               = ("HandOff"               / "HO")
 InactiveToken              = ("Inactive"              / "IN")
 IsolateToken               = ("Isolate"               / "IS")
 InSvcToken                 = ("InService"             / "IV")

Cuervo, et al. Standards Track [Page 105] RFC 2885 Megaco Protocol August 2000

 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")
 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")
 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")

Cuervo, et al. Standards Track [Page 106] RFC 2885 Megaco Protocol August 2000

 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")

ANNEX C TAGS FOR MEDIA STREAM PROPERTIES (NORMATIVE)

 Parameters for Local descriptors and Remote 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 section 7.1.1.
 For type "enumeration" the value is represented by the value in
 brackets, e.g., Send(0), Receive(1).

C.1 General Media Attributes

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

Cuervo, et al. Standards Track [Page 107] RFC 2885 Megaco Protocol August 2000

 ACodec              1006      Octet String     Audio Codec Type:
    Reference: ITU-T Rec. Q.765 - Application transport mechanism.
    Non-ITU codecs are defined with the appropriate standards
    organisation under a defined Organizational Identifier.
 Samplepp            1007      Unsigned         Maximum samples or
                               Integer          frames per packet: 0-
                                                65535
 Silencesupp         1008      BOOLEAN          Silence Suppression:
                                                True/false
 Encrypttype         1009      Octet string     Ref.: rec. H.245
 Encryptkey          100A      Octet string     Encryption key
                               SIZE(0..65535)
    Ref.: rec. H.235
 Echocanc           100B       Enumeration      Echo Canceller:
                                                Off(0), G.165(1),
                                                G168(2)
 Gain               100C       Unsigned         Gain in db: 0-65535
                               Integer
 Jitterbuff         100D       Unsigned         Jitter buffer size in
                               Integer          ms: 0-65535
 PropDelay          100E       Unsigned         Propagation Delay:
                               Integer          0..65535
    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

C.2 Mux Properties

 PropertyID     Property    Type                Value
                   Tag
 H.221              2001      Octet     Ref.: rec. H.245,
                              string    H222LogicalChannelParameters

Cuervo, et al. Standards Track [Page 108] RFC 2885 Megaco Protocol August 2000

 H223               2002      Octet     Ref.: rec. H.245,
                              string    H223LogicalChannelParameters
 V76                2003      Octet     Ref.: rec. H.245,
                              String    V76LogicalChannelParameters
 H2250              2004      Octet     Ref.: rec. H.245,
                              String    H2250LogicalChannelParameters

C.3 General bearer properties

 PropertyID     Property       Type                Value
                  Tag
 Mediatx            3001      Enumeration    Media Transport Type:
                                             TDM Circuit(0), ATM(1),
                                             FR(2), Ipv4(3), Ipv6(4),
                                             _
 BIR                3002      4 OCTET        Value depends on
                                             transport technology
 NSAP               3003      1-20 OCTETS    See NSAP
    Reference: ITU X.213 Annex A

C.4 General ATM properties

 PropertyID         Property  Type           Value
                    Tag
 AESA               4001      20 OCTETS      ATM End System Address
 VPVC               4002      2 x 16 bit     VPC/VCI
                              integer
 SC                 4003      4 bits         Service Category
    Reference: ITU Recommendation Q.2931 (1995)
 BCOB               4004      5 bit integer  Broadband Bearer Class
    Reference: ITU Recommendation Q.2961.2 (06/97)
 BBTC               4005      octet          Broadband Transfer
                                             Capability
    Reference: ITU Recommendation Q.2961 (10/95)
 ATC                4006      Enumeration    I.371 ATM Traffic
                                             Capability

Cuervo, et al. Standards Track [Page 109] RFC 2885 Megaco Protocol August 2000

    Reference: ITU Recommendation I.371:
    DBR(0), SBR1(1), SBR2(2), SBR(3), ABT/IT(4), ABT/DT(5), ABR(6)
 STC                4007      2 bits         Susceptibility to
                                             clipping
    Reference: ITU Recommendation Q.2931 (1995)
    00 Susceptible
    01 Not-susceptible
 UPCC               4008      2 bits         User Plane Connection
                                             configuration:
    Reference: ITU Recommendation Q.2931 (1995)
    00 Pt-to-pt,
    01 Pt-to-mpt
 PCR0               4009      24 bit         Peak Cell Rate (For
                              integer        CLP=0)
    Reference: ITU Recommendation I.371
 SCR0               400A      24 bit         Sustainable Cell Rate
                              integer        (For CLP=0)
    Reference: ITU Recommendation I.371
 MBS0               400B      24 bit         Maximum Burst Size (For
                              integer        CLP=0)
    Reference: ITU Recommendation I.371
 PCR1               400C      24 bit         Peak Cell Rate (For
                              integer        CLP=0+1)
    Reference: ITU Recommendation I.371
 SCR2               400D      24 bit         Sustainable Cell Rate
                              integer        (For CLP=0+1)
    Reference: ITU Recommendation I.371
 MBS3               400E      24 bit         Maximum Burst Size (For
                              integer        CLP=0+1)
    Reference: ITU Recommendation I.371
 BEI                400F      Boolean        Best Effort Indicator
 TI                 4010      Boolean        Tagging
 FD                 4011      Boolean        Frame Discard

Cuervo, et al. Standards Track [Page 110] RFC 2885 Megaco Protocol August 2000

 FCDV               4012      24 bit         Forward P-P CDV
                              integer
 BCDV               4013      24 bit         Backward P-P CDV
                              integer
 FCLR0              4014      8 bit integer  Forward Cell Loss Ratio
                                             (For CLP=0)
 BCLR0              4015      8 bit integer  Backward P-P Cell Loss
                                             Ratio (For CLP=0)
 FCLR1              4016      8 bit integer  Forward Cell Loss Ratio
 BCLR1              4017      8 bit integer  Backward P-P Cell Loss
                                             Ratio (For CLP=0+1)
 FCDV               4018      24 bit         Forward Cell Delay
                              integer        Variation
 BCDV               4019      24 bit         Backward Cell Delay
                              integer        Variation
 FACDV              401A      24 bit         Forward Acceptable P-P-P
                              integer        CDV
 BACDV              401B      24 bit         Backward Acceptable P-P
                              integer        CDV
 FCCDV              401C      24 bit         Forward Cumulative P-P
                              integer        CDV
 BCCDV              401D      24 bit         Backward Cumulative P-P
                              integer        CDV
 FCLR               401E      8 bit integer  Acceptable Forward Cell
                                             Loss Ratio
 BCLR               401F      8 bit integer  Acceptable Backward Cell
                                             Loss Ratio
 EETD               4020      16 bit         End-to-end transit delay
                              integer
 Mediatx (See       4021                     AAL Type
 General
 Properties)
    Reference: ITU Recommendation Q.2931 (1995)

Cuervo, et al. Standards Track [Page 111] RFC 2885 Megaco Protocol August 2000

 QosClass           4022      Integer 0-4    Qos Class
    Reference: ITU Recommendation Q.2931 (1995)
    QoS Parameter Application:
  Qos Class0  QoS                       ApplicationBest Effort
              Parameter Unspecified
      0       Unspecified               Best EffortConstant Bit rate
              Specified                 circuit emulation
      1       Specified                 Constant Bit rate circuit
              Specified                 emulationVariable bit rate
                                        video and audio
      2       Specified                 Variable bit rate video and
              Specified                 audioConnection-oriented data
      3       Specified                 Connection-oriented
              Specified                 dataConnectionless data
      4       Specified                 Connectionless data
 AALtype            4023      1 OCTET        AAL Type
    Reference: ITU Recommendation Q.2931 (1995)
    00000000        AAL for voice
    00000001        AAL type 1
    00000010        AAL type 2
    00000011        AAL type 3/4
    00000101        AAL type 5
    00010000        user defined AAL

C.5 Frame Relay

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

Cuervo, et al. Standards Track [Page 112] RFC 2885 Megaco Protocol August 2000

C.6 IP

 PropertyID       Property  Type               Value
                  Tag
 IPv4             6001      32 BITS            Ipv4Address:
                            Ipv4Address
    Reference: IETF RFC791
 IPv6             6002      128 BITS           IPv6 Address:
    Reference: IETF RFC2460
 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 Reference: ITU Recommendation Q.2630.1
    ESEA
    NSEA
 BIR              See C.3   4 OCTETS           Served user generated
                                               reference
    as defined in Reference: ITU Recommendation Q.2630.1
    SUGR
 ALC              7002      12 OCTETS          AAL2 link
                                               characteristics
    as defined in Reference: ITU Recommendation Q.2630.1
    max/average CPS-SDU bitrate,
    max/average CPS-SDU size
 SSCS             7003      I.366.2:                   Service
                            audio (8 OCTETS)           specific
                            multirate (3 OCTETS)       convergence
                            or I.366.1:                sublayer
                            SAR-assured (14 OCTETS)/   information
                            unassured (7 OCTETS)
    as defined in Reference: Q.2630.1 and used in I.366.1 and I.366.2
    I.366.2: audio/multirate

Cuervo, et al. Standards Track [Page 113] RFC 2885 Megaco Protocol August 2000

    I.366.1: SAR-assured/unassured
 SUT              7004      1..254 octets      Served user transport
                                               parameter
    as defined in Reference: ITU Recommendation Q.2630.1
 TCI              7005      BOOLEAN            Test connection
                                               indicator
    as defined in Reference: ITU Recommendation  Q.2630.1
 Timer_CU         7006      32 bit integer     Timer-CU: Milliseconds
                                               to hold partially
                                               filled cell before
                                               sending.
 MaxCPSSDU        7007      8 bit integer      Maximum Common Part
                                               Sublayer Service Data
                                               Unit
    Ref.: rec. Q.2630.1
 SCLP             7008      Boolean            Set Cell Local
                                               PriorityLP bit:
                                               True if CLP bit is to
                                               be set
 EETR             7009      Boolean            Timing Requirements
    Reference: ITU Recommendation Q.2931 (1995)
    End to End Timing Required:
    In broadband bearer capability
 CID              700A      8 bits             subchannel id, 0-255
    Ref.: rec. I.363.2 (09/97)

C.8 ATM AAL1

 PropertyID       Property  Type               Value
                  Tag
 BIR              See                          GIT (Generic
                  Table                        Identifier Transport)                              4 OCTETS
                  C.3
    Ref.: Recommendation Q.2941.1 (09/97)
 AAL1ST           8001      1 OCTET            AAL1 Subtype:
    Reference: ITU Recommendation Q.2931 (1995)
    00000000       Null

Cuervo, et al. Standards Track [Page 114] RFC 2885 Megaco Protocol August 2000

    00000001       voiceband signal transport on 64kbit/s
    00000010       circuit transport
    00000100       high-quality audio signal transport
    00000101       video signal transport
 CBRR             8002      1 OCTET            CBR Rate
    Reference: ITU Recommendation Q.2931 (1995)
    00000001           64 kbit/s
    00000100       1544 kbit/s
    00000101       6312 kbit/s
    00000110      32064 kbit/s
    00000111      44736 kbit/s
    00001000      97728 kbit/s
    00010000        2048 kbit/s
    00010001        8448 kbit/s
    00010010      34368 kbit/s
    00010011    139264 kbit/s
    01000000      n x 64 kbit/s
    01000001        n * 8 kbit/s
 MULT             See                          Multiplier, or n x
                  Table                        64k/8k/300
                  C.9
    Reference: ITU Recommendation Q.2931 (1995)
 SCRI             8003      1 OCTECT           Source Clock Frequency
                                               Recovery Method
    Reference: ITU Recommendation Q.2931 (1995)
    00000000    NULL
    00000001    SRTS
    00000010    ACM
 ECM              8004      1 OCTECT           Error Correction
                                               Method
    Reference: ITU Recommendation Q.2931 (1995)
    00000000    Null
    00000001    FEC-LOSS
    00000010    FEC-DELAY
 SDTB             8005      16 bit integer     Structured Data
                                               Transfer Blocksize
    Reference: ITU Recommendation I.363.1
    Block size of SDT CBR service
 PFCI             8006      8 bit integer      Partially filled cells
                                               indentifier
    Reference: ITU Recommendation I.363.1

Cuervo, et al. Standards Track [Page 115] RFC 2885 Megaco Protocol August 2000

    1-47
 EETR             See       See Table C.7      See Table C.7
                  Table
                  C.7

C.9 Bearer Capabilities

 PropertyID       Property  Type               Value
                  Tag
 TMR              9001      1 OCTET            Transmission Medium
                                               Requirement (Q.763)
    Reference: ITU Recommendation Q.763(09/97)
    Bit 8 7 6 5 4 3 2 1
    00000000 - speech
    00000001 - spare
    00000010 - 64 kbit/s unrestricted
    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
    00000111 - 2 x 64 kbit/s unrestricted
    00001000 - 384 kbit/s unrestricted
    00001001 - 1536 kbit/s unrestricted
    00001010 - 1920 kbit/s unrestricted
    00001011 through 00001111- spare
    00010000 - 3 x 64 kbit/s unrestricted
    00010001 - 4 x 64 kbit/s unrestricted
    00010010 -  5 x 64 kbit/s unrestricted
    00010011 spare
    00010100 - 7 x 64 kbit/s unrestricted
    00010101 - 8 x 64 kbit/s unrestricted
    00010110 - 9 x 64 kbit/s unrestricted
    00010111 - 10 x 64 kbit/s unrestricted
    00011000 - 11 x 64 kbit/s unrestricted
    00011001 - 12 x 64 kbit/s unrestricted
    00011010 - 13 x 64 kbit/s unrestricted
    00011011 - 14 x 64 kbit/s unrestricted
    00011100 - 15 x 64 kbit/s unrestricted
    00011101 - 16 x 64 kbit/s unrestricted
    00011110 - 17 x 64 kbit/s unrestricted
    00011111 - 18 x 64 kbit/s unrestricted
    00100000 - 19 x 64 kbit/s unrestricted
    00100001 - 20 x 64 kbit/s unrestricted

Cuervo, et al. Standards Track [Page 116] RFC 2885 Megaco Protocol August 2000

    00100010 - 21 x 64 kbit/s unrestricted
    00100011 - 22 x 64 kbit/s unrestricted
    00100100 - 23x 64 kbit/s unrestricted
    00100101 - spare
    00100110 - 25 x 64 kbit/s unrestricted
    00100111 - 26 x 64 kbit/s unrestricted
    00101000 - 27 x 64 kbit/s unrestricted
    00101001 - 28 x 64 kbit/s unrestricted
    00101010 - 29 x 64 kbit/s unrestricted
    00101011 through 11111111 Spare
 TMRSR            9002      1 OCTET            Transmission Medium
                                               Requirement Subrate
    0 - unspecified
    1 - 8kbit/s
    2 - 16kbit/s
    3 - 32kbit/s
 Contcheck        9003      BOOLEAN            Continuity Check
    Reference: ITU Recommendation Q.763(09/97)
    0 - Not required on this circuit
    1 - Required on this circuit
 ITC              9004      5 BITS             Information Transfer
                                               Capability
    Reference: ITU Recommendation Q.763(09/97)
    Bits 5 4 3 2 1
    00000 - Speech
    01000 -Unrestricted digital information
    01001- Restricted digital information
    10000 3.1 kHz audio
    10001 - Unrestricted digital information with tones/announcements
    (Note 2)
    11000 -Video
    All other values are reserved.
 TransMode        9005      2 BITS             Transfer Mode
    Reference: ITU Recommendation Q.931 (1998)
    Bit 2 1
    00 - Circuit mode
    10 - Packet mode
 TransRate        9006      5 BITS             Transfer Rate
    Reference: ITU Recommendation Q.931 (1998)
    Bit 5 4 3 2 1
    00000 - This code shall be used for packet mode calls
    10000 - 64 kbit/s

Cuervo, et al. Standards Track [Page 117] RFC 2885 Megaco Protocol August 2000

    10001 - 2 x 64 kbit/s
    10011 -384 kbit/s
    10101 -1536 kbit/s
    10111 -1920 kbit/s
    11000 - Multirate (64 kbit/s base rate)
 MULT             9007      7 BITS             Rate Multiplier
    Reference: ITU Recommendation Q.931 (1998)
    Any value from 2 to n (maximum number of B-channels)
 USI              9008      5 BITS             User Information Layer
                                               1 Protocol
    Reference: ITU Recommendation Q.931 (1998)
    Bits 5 4 3 2 1
    00001 - CCITT standardized rate adaption V.110 and X.30.
    00010 - Recommendation G.711  u-law
    00011 - Recommendation G.711 A-law
    00100 - Recommendation G.721 32 kbit/s ADPCM and Recommendation
    I.460.
    00101 - Recommendations H.221 and H.242
    00110 - Recommendations H.223 and H.245
    00111 - Non-ITU-T standardized rate adaption.
    01000 - ITU-T standardized rate adaption V.120.
    01001 - CCITT standardized rate adaption X.31 HDLC flag stuffing.
    All other values are reserved.
 syncasync        9009      BOOLEAN            Synchronous/
                                               Asynchronous
    Reference: ITU Recommendation Q.931 (1998)
    0 - Synchronous data
    1 - Asynchronous data
 negotiation      900A      BOOLEAN            Negotiation
    Reference: ITU Recommendation Q.931 (1998)
    0 - In-band negotiation possible
    1 - In-band negotiation not possible
 Userrate         900B      5 BITS             User Rate
    Reference: ITU Recommendation Q.931 (1998)
    Bits 5 4 3 2 1
    00000 - Rate is indicated by E-bits specified in Recommendation
    I.460  or may be negotiated in-band
    00001 - 0.6 kbit/s Recommendations V.6  and X.1
    00010 - 1.2 kbit/s Recommendation V.6
    00011 - 2.4 kbit/s Recommendations V.6 and X.1
    00100 - 3.6 kbit/s Recommendation V.6
    00101 - 4.8 kbit/s Recommendations V.6 and X.1
    00110 - 7.2 kbit/s RecommendationV.6

Cuervo, et al. Standards Track [Page 118] RFC 2885 Megaco Protocol August 2000

    00111 - 8 kbit/s Recommendation I.460
    01000 - 9.6 kbit/s Recommendations V.6 and X.1
    01001 - 14.4 kbit/s Recommendation V.6
    01010 - 16 kbit/s Recommendation I.460
    01011 - 19.2 kbit/s Recommendation V.6
    01100 - 32 kbit/s Recommendation I.460
    01101 - 38.4 kbit/s Recommendation V.110
    01110 - 48 kbit/s Recommendations V.6 and X.1
    01111 - 56 kbit/s Recommendation V.6
    10010 - 57.6 kbit/s Recommendation V.14 extended
    10011 - 28.8 kbit/s Recommendation V.110
    10100 - 24 kbit/s Recommendation V.110
    10101 - 0.1345 kbit/s Recommendation X.1
    10110 - 0.100 kbit/s Recommendation X.1
    10111 - 0.075/1.2 kbit/s Recommendations V.6 and X.1
    11000 - 1.2/0.075 kbit/s Recommendations V.6 and X.1
    11001 - 0.050 kbit/s Recommendations V.6 and X.1
    11010 - 0.075 kbit/s Recommendations V.6 and X.1
    11011 - 0.110 kbit/s Recommendations V.6 and X.1
    11100 - 0.150 kbit/s Recommendations V.6 and X.1
    11101 - 0.200 kbit/s Recommendations V.6 and X.1
    11110 - 0.300 kbit/s Recommendations V.6 and X.1
    11111 - 12 kbit/s Recommendation V.6
    All other values are reserved.
 INTRATE          900C      2 BITS             Intermediate Rate
    Reference: ITU Recommendation Q.931 (1998)
    Bit 2 1
    00 - Not used
    01 - 8 kbit/s
    10 - 16 kbit/s
    11 - 32 kbit/s
 nictx            900D      BOOLEAN            Network Independent
                                               Clock (NIC) on
                                               transmission
    Reference: ITU Recommendation Q.931 (1998)
    0 - Not required to send data with network independent clock
    1 - Required to send data with network independent clock
 nicrx            900E      BOOLEAN            Network independent
                                               clock (NIC) on
                                               reception
    Reference: ITU Recommendation Q.931 (1998)
    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 (i.e. sender
    does support this optional procedure)

Cuervo, et al. Standards Track [Page 119] RFC 2885 Megaco Protocol August 2000

 flowconttx       900F      BOOLEAN            Flow Control on
                                               transmission (Tx)
    Reference: ITU Recommendation Q.931 (1998)
    0 - Not required to send data with flow control mechanism
    1 - Required to send data with flow control mechanism
 flowcontrx       9010      BOOLEAN            Flow control on
                                               reception (Rx)
    Reference: ITU Recommendation Q.931 (1998)
    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)
 rateadapthdr     9011      BOOLEAN            Rate adaption
                                               header/no header
    Reference: ITU Recommendation Q.931 (1998)
    0 - Rate adaption header not included
    1 - Rate adaption header included
 multiframe       9012      BOOLEAN            Multiple frame
                                               establishment support
                                               in data link
    Reference: ITU Recommendation Q.931 (1998)
    0 - Multiple frame establishment not supported. Only UI frames
    allowed.
    1 - Multiple frame establishment supported
 OPMODE           9013      BOOLEAN            Mode of operation
    Reference: ITU Recommendation Q.931 (1998)
    0 Bit transparent mode of operation
    1 Protocol sensitive mode of operation
 llidnegot        9014      BOOLEAN            Logical link
                                               identifier negotiation
    Reference: ITU Recommendation Q.931 (1998)
    0 Default, LLI = 256 only
    1 Full protocol negotiation
 assign           9015      BOOLEAN            Assignor/assignee
    Reference: ITU Recommendation Q.931 (1998)
    0 Message originator is "Default assignee"
    1 Message originator is "Assignor only"
 inbandneg        9016      BOOLEAN            In-band/out-band
                                               negotiation
    Reference: ITU Recommendation Q.931 (1998)

Cuervo, et al. Standards Track [Page 120] RFC 2885 Megaco Protocol August 2000

    0- Negotiation is done with USER INFORMATION messages on a
    temporary signalling connection
    1- Negotiation is done in-band using logical link zero
 stopbits         9017      2 BITS             Number of stop bits
    Reference: ITU Recommendation Q.931 (1998)
    Bits 2 1
    00 - Not used
    01 - 1 bit
    10 - 1.5 bits
    11 - 2 bits
 databits         9018      2 BIT              Number of data bits
                                               excluding parity Bit
                                               if present
    Reference: ITU Recommendation Q.931 (1998)
    Bit 2 1
    00 - Not used
    01 - 5 bits
    10 - 7 bits
    11 - 8 bits
 parity           9019      3 BIT              Parity information
    Reference: ITU Recommendation Q.931 (1998)
    Bit 3 2 1
    000 - Odd
    010 - Even
    011 -None
    100 - Forced to 0
    101 - Forced to 1
    All other values are reserved.
 duplexmode       901A      BOOLEAN            Mode duplex
    Reference: ITU Recommendation Q.931 (1998)
    0 - Half duplex
    1 - Full duplex
 modem            901B      6 BIT              Modem Type
    Reference: ITU Recommendation Q.931 (1998)
    Bits 6 5 4 3 2 1
    00000 through 000101 National Use
    010001 - Recommendation V.21
    010010 - Recommendation V.22
    010011 - Recommendation V.22 bis
    010100 - Recommendation V.23
    010101 - Recommendation V.26
    011001 - Recommendation V.26 bis
    010111 -Recommendation V.26 ter

Cuervo, et al. Standards Track [Page 121] RFC 2885 Megaco Protocol August 2000

    011000 - RecommendationV.27
    011001 - Recommendation V.27 bis
    011010 - Recommendation V.27 ter
    011011 - Recommendation V.29
    011101 - Recommendation V.32
    011110 - Recommendation V.34
    100000 through 101111 National Use
    110000 through 111111 User Specified
 layer2prot       901C      5 BIT              User information layer
                                               2 protocol
    Reference: ITU Recommendation Q.931 (1998)
    Bit 5 4 3 2 1
    00010 - Recommendation Q.921/I.441 [3]
    00110 - Recommendation X.25 [5], link layer
    01100 - LAN logical link control (ISO/IEC 8802-2)
    All other values are reserved.
 layer3prot       901D      5 BIT              User information layer
                                               3 protocol
    Reference: ITU Recommendation Q.931 (1998)
    Bit 5 4 3 2 1
    00010 - Recommendation Q.931/I.451
    00110 - Recommendation X.25, packet layer
    01011 - ISO/IEC TR 9577 (Protocol identification in the network
    layer)
    All other values are reserved.
 addlayer3prot    901E      OCTET              Additional User
                                               Information layer 3
                                               protocol
    Reference: ITU Recommendation Q.931 (1998)
    Bits 4321 4321
    1100 1100 - Internet Protocol (RFC 791) (ISO/IEC TR 9577)
    1100 1111 - Point-to-point Protocol (RFC 1548)
 DialledN         901F      30 OCTETS          Dialled Number
 DiallingN        9020      30 OCTETS          Dialling Number
 ECHOCI           9021      Enumeration        Echo Control
                                               Information
    echo canceler off (0), incoming echo canceler on (1), outgoing
    echo canceler on (2), incoming and outgoing echo canceler on (3)
 NCI              9022      1 OCTET            Nature of Connection
                                               Indicators
    Reference: ITU Recommendation Q.763

Cuervo, et al. Standards Track [Page 122] RFC 2885 Megaco Protocol August 2000

    Bits 8 7 6 5 4 3 2 1
    Bits 2 1 Satellite Indicator
    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
    Bits 5 Echo control device indicator
    0  outgoing echo control device not included
    1   outgoing echo control device included
    Bits 8 7 6 Spare

C.10 AAL5 Properties

 PropertyID       Property  Type               Value
                  Tag
 FMSDU            A001      32 bit integer     Forward Maximum CPCS-
                                               SDU Size:
    Reference: ITU Recommendation Q.2931 (1995)
    Maximum CPCS-SDU size sent in the direction from the calling user
    to the called user.
 BMSDU            A002      32 bit integer     Backwards Maximum
                                               CPCS-SDU Size
    Reference: ITU Recommendation Q.2931 (1995)
    Maximum CPCS-SDU size sent in the direction from the called user
    to the calling user.
 SSCS             See       See table C.7      See table C.7
                  table
                  C.7
    Additional values:
    VPI/VCI
 SC               See       See Table C.4      See table C.4
                  Table
                  C.4

Cuervo, et al. Standards Track [Page 123] RFC 2885 Megaco Protocol August 2000

C.11 SDP Equivalents

 PropertyID       Property  Type               Value
                  Tag
 SDP_V            B001      STRING             Protocol Version
 SDP_O            B002      STRING             Owner/creator and
                                               session ID
 SDP_S            B003      STRING             Sesson name
 SDP_I            B004      STRING             Session identifier
 SDP_U            B005      STRING             URI of descriptor
 SDC_E            B006      STRING             email address
 SDP_P            B007      STRING             phone number
 SDP_C            B008      STRING             Connection information
 SDP_B            B009      STRING             Bandwidth Information
 SDP_Z            B00A      STRING             time zone adjustment
 SDP_K            B00B      STRING             Encryption Key
 SDP_A            B00C      STRING             Zero or more session
                                               attributes
 SDP_T            B00D      STRING             Active Session Time
 SDP_R            B00E      STRING             Zero or more repeat
                                               times
    Reference in all cases: IETF RFC2327, "Session Description
    Protocol"

C.12 H.245

 PropertyID       Property  Type           Value
                  Tag
 OLC              C001      octet string   The value of H.245
                                           OpenLogicalChannel
                                           structure.

Cuervo, et al. Standards Track [Page 124] RFC 2885 Megaco Protocol August 2000

 OLCack           C002      octet string   The value of H.245
                                           OpenLogicalChannelAck
                                           structure.
 OLCcnf           C003      octet string   The value of H.245
                                           OpenLogicalChannelConfirm
                                           structure.
 OLCrej           C004      octet string   The value of H.245
                                           OpenLogicalChannelReject
                                           structure.
 CLC              C005      octet string   The value of H.245
                                           CloseLogicalChannel
                                           structure.
 CLCack           C006      octet string   The value of H.245
                                           CloseLogicalChannelAck
                                           structure.
    Reference in all cases: ITU-T Recommendation H.245

ANNEX D TRANSPORT OVER IP (NORMATIVE)

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

 Protocol messages defined in this document may be transmitted over
 UDP.  When no port is provided by the peer (see section 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 except if the response is to a handoff or
 failover, in which case the procedures of 11.5 apply.
 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

Cuervo, et al. Standards Track [Page 125] RFC 2885 Megaco Protocol August 2000

 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 section 8.2.3 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
 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

Cuervo, et al. Standards Track [Page 126] RFC 2885 Megaco Protocol August 2000

 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.
 Messages that carry the "Transaction Response Acknowledgement"
 parameter may be transmitted in any order.  The entity shall retain
 the "confirmed transaction-id ranges" receivedfor LONG-TIMER seconds.
 In the binary encoding, if only the firstAck is present in a response
 acknowledgement (see Annex 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 Annex B.2).

D.1.3 Computing retransmission timers

 It is the responsibility of the requesting entity to provide suitable
 time outs for all outstanding transactions, and to retry transactions
 when time outs 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.
 Note -  One possibility is to use the algorithm implemented in TCP-
 IP, which uses two variables:
  .  The average acknowledgement delay, AAD, estimated through an
     exponentially smoothed average of the observed delays.
  .  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

Cuervo, et al. Standards Track [Page 127] RFC 2885 Megaco Protocol August 2000

     document, 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.
 After any retransmission, the entity should do the following:
  .  It should double the estimated value of the average delay, AAD
  .  It should compute a random value, uniformly distributed between
     0.5 AAD and AAD
  .  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".
 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, an immediate
 confirmation shall be sent, and normal repetition timers shall be
 used thereafter.  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 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

Cuervo, et al. Standards Track [Page 128] RFC 2885 Megaco Protocol August 2000

 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:
  .  transmission errors, when for example a packet is lost due to
     noise on a line or congestion in a queue;
  .  component failure, when for example an interface to a entity
     becomes unavailable;
  .  entity failure, when for example an entire entity become
     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 1 000 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 document
 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

Cuervo, et al. Standards Track [Page 129] RFC 2885 Megaco Protocol August 2000

 connectivity 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. When the MG
 establishes a new control association, it can retransmit to the new
 MGC.  Alternatively, a MG may use a ServiceChange with
 ServiceChangeMethod equal to disconnected to inform the new MGC 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 document may be transmitted over
 TCP.  When no port is specified by the other side (see section
 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 RFC1006 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 section 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 section D.1.2.2.

Cuervo, et al. Standards Track [Page 130] RFC 2885 Megaco Protocol August 2000

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 section 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 behavior under congestion, and in particular, could
 reorder transactions when congestion is encountered.  TCP could not
 achieve the same results.

ANNEX E BASIC PACKAGES

 This Annex contains definitions of some packages for use with the
 Megaco protocol.

E.1 Generic

 PackageID: g (0x000e)
 Version: 1
 Extends: None
 Description: Generic package for commonly encountered items.

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E.1.1 Properties

 None

E.1.2 Events

 Cause
 -----
 EventID:     cause (0x0001)
 Generic error event
 ObservedEvents Descriptor Parameters:
      General Cause
      -------------
      ParameterID: Generalcause (0x0001)
      Description: This parameter groups the failures into six
      groups, which the MGC may act upon.
      Possible values:        Enumerated,
              "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)
      Description: The Release 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.
      Possible Values: OCTET STRING
 Signal Completion
 -----------------
 EventID: sc (0x0002)
 Indicates termination of one or more signals for which the
 notifyCompletion parameter was set to "ON".  For further procedural
 description, see sections 7.1.11, 7.1.17, and 7.2.7.

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 ObservedEvents Descriptor parameters:
      Signal Identity
      ---------------
      ParameterID:  SigID (0x0001)
      This parameter identifies the signals which have terminated.
      Type: list
      Possible values: a list of signals and/or sequential signal
      lists which have terminated.  A signal outside of a sequential
      signal list shall be identified using the pkgdName syntax
      without wildcarding.  An individual signal inside of a
      sequential signal list shall be identified using the sequential
      signal list syntax with the correct signal list identifier,
      enclosing the name of the specific signal which terminated in
      pkgdName syntax.
      Termination Method
      ------------------
      ParameterID:  Meth (0x0002)
      Indicates the means by which the signal terminated.
      Type: enumeration
      Possible values:
              "TO" (0x0001) Duration expired
              "EV" (0x0002) Interrupted by event
              "SD" (0x0003) Halted by new Signals Descriptor
              "NC" (0x0004) Not completed, other cause

E.1.3 Signals

 None

E.1.4 Statistics

 None

E.2 Base Root Package

 Base Root Package
 PackageID: root (0x000f)
 Version: 1
 Extends: None

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 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
 MaxTerminationsPerContext
 -------------------------
 PropertyID: maxTerminationsPerContext (0x0002)
 The maximum number of allowed terminations in a context, see section
 6.1
 Type: Integer
 Possible Values: any integer
 Defined In: TerminationState
 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
 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)

Cuervo, et al. Standards Track [Page 134] RFC 2885 Megaco Protocol August 2000

 Type: Integer
 Possible Values: any integer, represents milliseconds
 ProvisionalResponseTimerValue
 -----------------------------
 PropertyId: ProvisionalResponseTimerValue (0x0005)
 Indicates the time within which to expect a Pending Response if a
 Transaction cannot be completed.  Initially set to
 normalMGExecutionTime or normalMGCExecutionTime as appropriate, plus
 network delay, but may be lowered.

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 (0x0001)
 Version: 1
 Extends: None
 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.

E.3.1 Properties

 None

Cuervo, et al. Standards Track [Page 135] RFC 2885 Megaco Protocol August 2000

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
 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

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E.4 Tone Detection Package

 PackageID: tonedet (0x0002)
 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.
 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 is implementation dependent.
 EventsDescriptor parameters:
      Tone id list
      ------------
      ParameterID: tl (0x0001)
      Type:  list of tone ids
      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

Cuervo, et al. Standards Track [Page 137] RFC 2885 Megaco Protocol August 2000

      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
      This parameter contains the duration of the tone from first
      detection until it stopped.
 Long tone detected
 ------------------
 EventID: ltd, 0x0003

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 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)
      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

E.4.5 Procedures

 None

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E.5 Basic DTMF Generator Package

 PackageID: dg (0x0003) 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 toneid 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 toneid, thus
 extending the basic tone generation package.  Also note that dtmf
 SignalIds are different from the names used in a digit map.

Cuervo, et al. Standards Track [Page 140] RFC 2885 Megaco Protocol August 2000

              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 (0x0004)
 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 section 7.1.14.

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              DTMF                Event  Symbol
              d0                  "0"
              d1                  "1"
              d2                  "2"
              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 section E.5.3.
 DigitMap Completion Event
 -------------------------
 EventID: ce, 0x0001
 Generated when a digit map completes as described in section 7.1.14.
 EventsDescriptor parameters: digit map processing is activated only
 if a digit map parameter is present, specifying a digit map by name
 or by value.  Other parameters such as a KeepActive flag or embedded
 Events or Signals Descriptors may be present.
 ObservedEventsDescriptor parameters:
      DigitString
      -----------
      ParameterID: ds (0x0001)

Cuervo, et al. Standards Track [Page 142] RFC 2885 Megaco Protocol August 2000

      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 "L".
      Description: the portion of the current dial string as
      described in section 7.1.14 which matched part or all of an
      alternative event sequence specified in the digit map.
      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 section 7.1.14.

E.6.3 Signals

 None

E.6.4 Statistics

 None

E.6.5 Procedures

 None

E.7 Call Progress Tones Generator Package

 PackageID: cg, 0x0005
 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.

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E.7.1 Properties

 None

E.7.2 Events

 None

E.7.3 Signals

 Dial Tone
 ---------
 SignaID: 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 toneid, 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   pt (0x0036)
          Call Waiting Tone           cw (0x0037)
          Caller Waiting Tone         cr (0x0038)

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E.7.4 Statistics

 None

E.7.5 Procedures

 NOTE -  The required set of tone ids corresponds to those defined in
 Recommendation E.180/Q.35 [ITU-T Recommendation E.180/Q.35 (1998)].
 See E.180 for definition of the meanings of these tones.

E.8 Call Progress Tones Detection Package

 PackageID: cd (0x0006)
 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
 -----------------
 tone id 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
 [ITU-T Recommendation E.180/Q.35 (1998)].  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 section E.7.3

E.8.3 Signals

 none

E.8.4 Statistics

 none

Cuervo, et al. Standards Track [Page 145] RFC 2885 Megaco Protocol August 2000

E.8.5 Procedures

 none

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 immediately generate an on-hook
 event.
 EventDescriptor parameters
 None
 ObservedEventsDescriptor parameters
 None
 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 immediately generate an off-
 hook event.
 EventDescriptor parameters
 None

Cuervo, et al. Standards Track [Page 146] RFC 2885 Megaco Protocol August 2000

 ObservedEventsDescriptor parameters
 None
 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
 Additional Parameters:
      Cadence

Cuervo, et al. Standards Track [Page 147] RFC 2885 Megaco Protocol August 2000

  1. ——

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

 None

E.10 Basic Continuity Package

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

Cuervo, et al. Standards Track [Page 148] RFC 2885 Megaco Protocol August 2000

 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)
 The signal is used to respond to a continuity test .  See section
 E.10.5 for further explanation.
 Signal Type: TimeOut
 Default duration is provisioned
 Additional Parameters:
 None.

Cuervo, et al. Standards Track [Page 149] RFC 2885 Megaco Protocol August 2000

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
  .  a signals descriptor with the ct signal, and
  .  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 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
 awaits reception of the continuity test tone.  When the tone is
 received before the rsp signal times out, the MG returns the
 applicable return tone.  If the rsp signal times out, the MG removes
 the detection and the return tone (if that was playing).
 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.

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.

Cuervo, et al. Standards Track [Page 150] RFC 2885 Megaco Protocol August 2000

 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
 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, propogation delay and then indicating this using
 a percentage of quality loss.
 EventDescriptor parameters
      Threshold
      ---------
      ParameterId: th (0x0001)

Cuervo, et al. Standards Track [Page 151] RFC 2885 Megaco Protocol August 2000

      Type: integer
      Possible Values: 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: 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

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

Cuervo, et al. Standards Track [Page 152] RFC 2885 Megaco Protocol August 2000

 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.
 EventDescriptor parameters
 None
 ObservedEventsDescriptor parameters
      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)

Cuervo, et al. Standards Track [Page 153] RFC 2885 Megaco Protocol August 2000

 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.
 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 is used to support TDM circuit terminations.

Cuervo, et al. Standards Track [Page 154] RFC 2885 Megaco Protocol August 2000

E.13.1 Properties

 Echo Cancellation
 -----------------
 PropertyID: ec (0x0008)
 By default, the telephony gateways always perform echo cancellation.
 However, it is necessary, for some calls, to turn off these
 operations.
 Type: boolean
 Possible Values:
      "on" (when the echo cancellation is requested) and
      "off" (when it is turned off.)
 The default is "on".
 Defined In: LocalControlDescriptor
 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: enumeration (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

Cuervo, et al. Standards Track [Page 155] RFC 2885 Megaco Protocol August 2000

E.13.4 Statistics

 None

E.13.5 Procedures

 None

Cuervo, et al. Standards Track [Page 156] RFC 2885 Megaco Protocol August 2000

APPENDIX A EXAMPLE CALL FLOWS (INFORMATIVE)

 All Megaco implementors must read the normative part of this document
 carefully before implementing from it. No one should use the examples
 in this section as stand-alone explanations of how to create protocol
 messages.
 The examples in this section use SDP for encoding of the Local and
 Remote stream descriptors. SDP is defined in RFC 2327. If there is
 any discrepancy between the SDP in the examples, and RFC 2327, the
 RFC should be consulted for correctness. Audio profiles used are
 those defined in RFC 1890, and others registered with IANA. For
 example, G.711 A-law is called PCMA in the SDP, and is assigned
 profile 0. G.723 is profile 4, and H263 is profile 34. See also
      http://www.iana.org/numbers.htm#R

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.

Cuervo, et al. Standards Track [Page 157] RFC 2885 Megaco Protocol August 2000

 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 = - {
         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.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555
 Transaction = 9999 {
     Context = - {
         Modify = A4444 {
             Media { Stream = 1 {
                      LocalControl {
                          Mode = SendReceive,
                          ds0/gain=2,  ; in dB,
                          ds0/ec=G165
                      },
                      Local {
 v=0
 c=IN IP4 $

Cuervo, et al. Standards Track [Page 158] RFC 2885 Megaco Protocol August 2000

 m=audio $ RTP/AVP 0
 a=fmtp:PCMU VAD=X-NNVAD ; special voice activity
                         ; detection algorithm
                      }
                  }
             },
             Events = 2222 {al/of}
         }
     }
 }
 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).
 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}}

Cuervo, et al. Standards Track [Page 159] RFC 2885 Megaco Protocol August 2000

    }
 }
 7. And the Notify is acknowledged.
 MGC to MG1:
 MEGACO/1 [123.123.123.4]:55555
 Reply = 10000 {
     Context = - {Notify = A4444}
 }
 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, 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 {

Cuervo, et al. Standards Track [Page 160] RFC 2885 Megaco Protocol August 2000

          19990729T22010001:dd/ce{ds="916135551212",Meth=FM}}}
    }
 }
 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
 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
                   }
              }
           }
        }
     }
 }

Cuervo, et al. Standards Track [Page 161] RFC 2885 Megaco Protocol August 2000

 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.
 MEGACO/1 [124.124.124.222]:55555
 Reply = 10003 {
    Context = 2000 {
       Add = A4444,
       Add=A4445{
          Media {
              Stream = 1 {
                  Local {
 v=0
 c=IN IP4 124.124.124.222
 m=audio 2222 RTP/AVP 4
 a=ptime:30
 a=recvonly
                  } ; RTP profile for G.723 is 4
              }
          }
       }
    }
 }
 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}
             Signals {al/ri}
             },
        Add  = $ {Media {
             Stream = 1 {
                  LocalControl {
                     Mode = SendReceive,
                     nt/jit=40 ; in ms
                  },

Cuervo, et al. Standards Track [Page 162] RFC 2885 Megaco Protocol August 2000

                  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 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 [124.124.124.222]:55555
 Reply = 50003 {
    Context = 5000 {
      Add = A5555{}
       Add = A5556{
          Media {
             Stream = 1 {
                 Local {
 v=0
 c=IN IP4 125.125.125.111
 m=audio 1111 RTP/AVP 4
 }
             } ; RTP profile for G723 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 {

Cuervo, et al. Standards Track [Page 163] RFC 2885 Megaco Protocol August 2000

       Signals {cg/rt}
     },
     Modify = A4445 {
        Media {
             Stream = 1 {
                 Remote {
 v=0
 c=IN IP4 125.125.125.111
 m=audio 1111 RTP/AVP 4
                 }
             } ; RTP profile for G723 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.
 From MG2 to MGC:
 MEGACO/1 [125.125.125.111]:55555
 Transaction = 50005 {
    Context = 5000 {
        Notify = A5555 {ObservedEvents =1234 {
          19990729T22020002:al/of}}
    }
 }
 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 {

Cuervo, et al. Standards Track [Page 164] RFC 2885 Megaco Protocol August 2000

    Context = 5000 {
       Modify = A5555 {
          Events = 1235 {al/on},
          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 { }
       }
    }
 }
 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.
 MEGACO/1 [123.123.123.4]:55555
 Transaction = 50007 {
    Context = - {AuditValue = A5556{
       Audit{Media, DigitMap, Events, Signals, Packages, Statistics
 }}

Cuervo, et al. Standards Track [Page 165] RFC 2885 Megaco Protocol August 2000

    }
 }
 20. The MG2 replies. An RTP termination has no events nor signals,
 so these are left out in the reply .
 MEGACO/1 [125.125.125.111]:55555
 Reply = 50007 {
    Context = - {
 AuditValue = A5556 {
           Media {
              Stream = 1 {
                  LocalControl { Mode = SendReceive,
                     nt/jit=40 },
                  Local {
 v=0
 c=IN IP4 125.125.125.111
 m=audio 1111 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
                  } } },
           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
        }
     }
 }
 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 {

Cuervo, et al. Standards Track [Page 166] RFC 2885 Megaco Protocol August 2000

           19990729T24020002:al/on}
        }
    }
 }
 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
              nt/os=62345, ; octets sent
              rtp/pr=780, ; packets received
              nt/or=45123, ; octets received
              rtp/pl=10, ;  % packets lost
              rtp/jit=27,

Cuervo, et al. Standards Track [Page 167] RFC 2885 Megaco Protocol August 2000

              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.

Authors' Addresses

 Fernando Cuervo
 Nortel Networks
 P.O. Box 3511, Station C
 Ottawa, ON K1Y 4H7
 Canada
 E-mail: fcuervo@nortelnetworks.com
 Nancy Greene
 Nortel Networks
 P.O. Box 3511, Station C
 Ottawa, ON K1Y 4H7
 Canada
 E-mail: ngreene@nortelnetworks.com
 Christian Huitema
 Microsoft Corporation
 One Microsoft Way
 Redmond, WA 98052-6399
 USA
 E-mail: huitema@microsoft.com
 Abdallah Rayhan
 Nortel Networks
 P.O. Box 3511, Station C
 Ottawa, ON K1Y 4H7
 Canada
 E-mail: arayhan@nortelnetworks.com

Cuervo, et al. Standards Track [Page 168] RFC 2885 Megaco Protocol August 2000

 Brian Rosen
 Marconi
 1000 FORE Drive
 Warrendale, PA 15086
 USA
 E-mail: brian.rosen@marconi.com
 John Segers
 Lucent Technologies, Room HE 303
 Dept. Forward Looking Work
 P.O. Box 18, 1270 AA  Huizen
 The Netherlands
 E-mail: jsegers@lucent.com

Cuervo, et al. Standards Track [Page 169] RFC 2885 Megaco Protocol August 2000

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Cuervo, et al. Standards Track [Page 170]

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