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rfc:rfc2805

Network Working Group N. Greene Request for Comments: 2805 Nortel Networks Category: Informational M. Ramalho

                                                         Cisco Systems
                                                              B. Rosen
                                                               Marconi
                                                            April 2000
    Media Gateway Control Protocol Architecture and Requirements

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

 This document describes protocol requirements for the Media Gateway
 Control Protocol between a Media Gateway Controller and a Media
 Gateway.

Greene, et al. Informational [Page 1] RFC 2805 MG Control Protocol Requirements April 2000

Table of Contents

 1.  Introduction ..............................................  3
 2.  Terminology ...............................................  3
 3.  Definitions ...............................................  3
 4.  Specific functions assumed within the MG ..................  5
 5.  Per-Call Requirements .....................................  6
    5.1.  Resource Reservation .................................  6
    5.2.  Connection Requirements ..............................  7
    5.3.  Media Transformations ................................  8
    5.4.  Signal/Event Processing and Scripting ................  9
    5.5.  QoS/CoS .............................................. 10
    5.6.  Test Support ......................................... 11
    5.7.  Accounting ........................................... 11
    5.8.  Signalling Control ................................... 11
 6.  Resource Control .......................................... 12
    6.1.  Resource Status Management ........................... 12
    6.2.  Resource Assignment .................................. 13
 7.  Operational/Management Requirements ....................... 13
    7.1.  Assurance of Control/Connectivity .................... 13
    7.2.  Error Control ........................................ 14
    7.3.  MIB Requirements ..................................... 15
 8.  General Protocol Requirements ............................. 15
    8.1.  MG-MGC Association Requirements ...................... 16
    8.2.  Performance Requirements ............................. 17
 9.  Transport ................................................. 17
    9.1.  Assumptions made for underlying network .............. 17
    9.2.  Transport Requirements ............................... 18
 10.  Security Requirements .................................... 18
 11.  Requirements specific to particular bearer types ......... 19
    11.1.  Media-specific Bearer types ......................... 20
       11.1.1.  Requirements for TDM PSTN (Circuit) ............ 20
       11.1.2.  Packet Bearer type ............................. 22
       11.1.3.  Bearer type requirements for ATM ............... 23
    11.2.  Application-Specific Requirements ................... 26
       11.2.1.  Trunking Gateway ............................... 26
       11.2.2.  Access Gateway ................................. 27
       11.2.3.  Trunking/Access Gateway with fax ports ......... 27
       11.2.4.  Trunking/Access Gateway with text telephone .... 28
       11.2.5.  Network Access Server .......................... 29
       11.2.6.  Restricted Capability Gateway .................. 30
       11.2.7.  Multimedia Gateway ............................. 31
       11.2.8.  Audio Resource Function ........................ 32
       11.2.9. Multipoint Control Units ........................ 42
 12.  References ............................................... 43
 13.  Acknowledgements ......................................... 43
 14.  Authors' Addresses ....................................... 44
 15.  Full Copyright Statement ................................. 45

Greene, et al. Informational [Page 2] RFC 2805 MG Control Protocol Requirements April 2000

1. Introduction

 This document describes requirements to be placed on the Media
 Gateway Control Protocol. When the word protocol is used on its own
 in this document it implicitly means the Media Gateway Control
 Protocol.

2. Terminology

 In this document, the key words "MUST", "MUST NOT", "REQUIRED",
 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
 and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
 indicate requirement levels for the protocol.

3. Definitions

  • Connection
 Under the control of a Media Gateway Controller (MGC), the Media
 Gateway (MG) realizes connections. In this document, connections are
 associations of resources hosted by the MG. They typically involve
 two terminations, but may involve more.
  • Line or Loop
 An analogue or digital access connection from a user terminal which
 carries user media content and telephony access signalling (DP, DTMF,
 BRI, proprietary business set).
  • Media Gateway (MG) function
 A Media Gateway (MG) function provides the media mapping and/or
 transcoding functions between potentially dissimilar networks, one of
 which is presumed to be a packet, frame or cell network.  For
 example, an MG might terminate switched circuit network (SCN)
 facilities (trunks, loops), packetize the media stream, if it is not
 already packetized, and deliver packetized traffic to a packet
 network.  It would perform these functions in the reverse order for
 media streams flowing from the packet network to the SCN.
 Media Gateways are not limited to SCN <-> packet/frame/cell
 functions: A conference bridge with all packet interfaces could be an
 MG, as well as an (IVR) interactive voice recognition unit, an audio
 resource function, or a voice recognition system with a cell
 interface.

Greene, et al. Informational [Page 3] RFC 2805 MG Control Protocol Requirements April 2000

  • Media Gateway unit (MG-unit)
 An MG-unit is a physical entity that contains an MG function and may
 also contain other functions, e.g. an SG function.
  • Media Gateway Controller (MGC) function
 A Media Gateway Controller (MGC) function controls a MG.
  • Media Resource
 Examples of media resources are codecs, announcements, tones, and
 modems, interactive voice response (IVR) units, bridges, etc.
  • Signaling Gateway (SG) function
 An SG function receives/sends SCN native signalling at the edge of a
 data network. For example the SG function may relay, translate or
 terminate SS7 signaling in an SS7-Internet Gateway. The SG function
 may also be co-resident with the MG function to process SCN
 signalling associated with line or trunk terminations controlled by
 the MG, such as the "D" channel of an ISDN PRI trunk.
  • Termination
 A termination is a point of entry and/or exit of media flows relative
 to the MG. When an MG is asked to connect two or more terminations,
 it understands how the flows entering and leaving each termination
 are related to each other.
 Terminations are, for instance, DS0's, ATM VCs and RTP ports. Another
 word for this is bearer point.
  • Trunk
 An analog or digital connection from a circuit switch which carries
 user media content and may carry telephony signalling (MF, R2, etc.).
 Digital trunks may be transported and may appear at the Media Gateway
 as channels within a framed bit stream, or as an ATM cell stream.
 Trunks are typically provisioned in groups, each member of which
 provides equivalent routing and service.
  • Type of Bearer
 A Type of Bearer definition provides the detailed requirements for
 its particular application/bearer type. A particular class of Media
 Gateway, for example, would support a particular set of Bearer types.

Greene, et al. Informational [Page 4] RFC 2805 MG Control Protocol Requirements April 2000

4. Specific functions assumed within the MG

 This section provides an environment for the definition of the
 general Media Gateway Control Protocol requirements.
 MGs can be architected in many different ways depending where the
 media conversions and transcoding (if required) are performed, the
 level of programmability of resources, how conferences are supported,
 and how associated signalling is treated. The functions assumed to be
 within the MG must not be biased towards a particular architecture.
 For instance, announcements in a MG could be provided by media
 resources or by the bearer point resource or termination itself.
 Further, this difference must not be visible to MGC: The MGC must be
 able to issue the identical request to two different implementations
 and achieve the identical functionality.
 Depending on the application of the MG (e.g., trunking, residential),
 some functions listed below will be more prominent than others, and
 in some cases, functions may even disappear.
 Although media adaptation is the essence of the MG, it is not
 necessary for it to be involved every time. An MG may join two
 terminations/resources of the same type (i.e., the MG behaves as a
 switch). The required media conversion depends on the media type
 supported by the resources being joined together.
 In addition to media adaptation function, resources have a number of
 unique properties, for instance:
  • certain types of resources have associated signalling

capabilities (e.g., PRI signalling, DTMF),

  • some resources perform maintenance functions (e.g., continuity

tests),

  • the MGC needs to know the state changes of resources (e.g., a

trunk group going out of service),

  • the MG retains some control over the allocation and control of

some resources (e.g., resource name space: RTP port numbers).

 Therefore, an MG realizes point-to-point connections and conferences,
 and supports several resource functions. These functions include
 media conversion, resource allocation and management, and event
 notifications.  Handling termination associated signalling is either
 done using event notifications, or is handled by the signalling
 backhaul part of a MG-unit (i.e. NOT directly handled by the MG).

Greene, et al. Informational [Page 5] RFC 2805 MG Control Protocol Requirements April 2000

 MGs must also support some level of system related functions, such as
 establishing and maintaining some kind of MG-MGC association. This is
 essential for MGC redundancy, fail-over and resource sharing.
 Therefore, an MG is assumed to contain these functions:
  • Reservation and release, of resources
  • Ability to provide state of resources
  • Maintenance of resources - It must be possible to make

maintenance operations independent of other termination

      functions, for instance, some maintenance states should not
      affect the resources associated with that resource . Examples of
      maintenance functions are loopbacks and continuity tests.
  • Connection management, including connection state.
  • Media processing, using media resources: these provide services

such as transcoding, conferencing, interactive voice recognition

      units, audio resource function units. Media resources may or may
      not be directly part of other resources.
  • Incoming digit analysis for terminations, interpretation of

scripts for terminations

  • Event detection and signal insertion for per-channel signalling
  • Ability to configure signalling backhauls (for example, a

Sigtran backhaul)

  • Management of the association between the MGC and MG, or between

the MGC and MG resources.

5. Per-Call Requirements

5.1. Resource Reservation

 The protocol must:
 a.   Support reservation of bearer terminations and media resources
      for use by a particular call and support their subsequent
      release (which may be implicit or explicit).
 b.   Allow release in a single exchange of messages, of all resources
      associated with a particular set of connectivity and/or
      associations between a given number terminations.

Greene, et al. Informational [Page 6] RFC 2805 MG Control Protocol Requirements April 2000

 c.   The MG is not required (or allowed) by the protocol to maintain
      a sense of future time: a reservation remains in effect until
      explicitly released by the MGC.

5.2. Connection Requirements

 The protocol must:
 a.   Support connections involving packet and circuit bearer
      terminations in any combination, including "hairpin" connections
      (connections between two circuit connections within the same
      MG).
 b.   Support connections involving TDM, Analogue, ATM, IP or FR
      transport in any combination.
 c.   Allow the specification of bearer plane (e.g. Frame Relay, IP,
      etc.) on a call by call basis.
 d.   Support unidirectional, symmetric bi-directional, and asymmetric
      bi-directional flows of media.
 e.   Support multiple media types (e.g. audio, text, video, T.120).
 f.   Support point-to-point and point-to-multipoint connections.
 g.   Support creation and modification of more complex flow
      topologies e.g. conference bridge capabilities.  Be able to add
      or delete media streams during a call or session, and be able to
      add or subtract participants to/from a call or session.
 h.   Support inclusion of media resources into call or session as
      required.  Depending on the protocol and resource type, media
      resources may be implicitly included, class-assigned, or
      individually assigned.
 i.   Provide unambiguous specification of which media flows pass
      through a point and which are blocked at a given point in time,
      if the protocol permits multiple flows to pass through the same
      point.
 j.   Allow modifications of an existing termination, for example, use
      of higher compression to compensate for insufficient bandwidth
      or changing transport network connections.
 k.   Allow the MGC to specify that a given connection has higher
      priority than other connections.

Greene, et al. Informational [Page 7] RFC 2805 MG Control Protocol Requirements April 2000

 l.   Allow a reference to a port/termination on the MG to be a
      logical identifier,
      with a one-to-one mapping between a logical identifier and a
      physical port.
 m.   Allow the MG to report events such as resource reservation and
      connection completion.

5.3. Media Transformations

 The Protocol must:
 a.   Support mediation/adaptation of flows between different types of
      transport
 b.   Support invocation of additional processing such as echo
      cancellation.
 c.   Support mediation of flows between different content encoding
      (codecs, encryption/decryption)
 d.   Allow the MGC to specify whether text telephony/FAX/data modem
      traffic is to be terminated at the MG, modulated/demodulated,
      and converted to packets or forwarded by the MG in the media
      flow as voice band traffic.
 e.   Allow the MGC to specify that Dual-Tone MultiFrequency (DTMF)
      digits or other line and trunk signals and general Multi-
      Frequency (MF) tones are to be processed in the MG and how these
      digits/signals/tones are to be handled. The MGC must be able to
      specify any of the following handling of such
      digits/signals/tones:
 1.   The digits/signals/tones are to be encoded normally in the audio
      RTP stream (e.g., no analysis of the digits/signals/tones).
 2.   Analyzed and sent to the MGC.
 3.   Received from the MGC and inserted in the line-side audio
      stream.
 4.   Analyzed and sent as part of a separate RTP stream (e.g., DTMF
      digits sent via a RTP payload separate from the audio RTP
      stream).
 5.   Taken from a separate RTP stream and inserted in the line-side
      audio stream.

Greene, et al. Informational [Page 8] RFC 2805 MG Control Protocol Requirements April 2000

 6.   Handled according to a script of instructions.  For all but the
      first case, an option to mute the digits/signals/tones with
      silence, comfort noise, or other means (e.g., notch filtering of
      some telephony tones) must be provided.  As detection of these
      events may take up to tens of milliseconds, the first few
      milliseconds of such digit/signal/tone may be encoded and sent
      in the audio RTP stream before the digit/signal/tone can be
      verified. Therefore muting of such digits/signals/tones in the
      audio RTP stream with silence or comfort noise is understood to
      occur at the earliest opportunity after the digit/signal/tone is
      verified.
 f.   Allow the MGC to specify signalled flow characteristics on
      circuit as well as on packet bearer connections, e.g. u-law/a-
      law.
 g.   Allow for packet/cell transport adaptation only (no media
      adaptation) e.g. mid-stream (packet-to-packet)
      transpacketization/transcoding, or ATM AAL5 to and from ATM AAL2
      adaptation.
 h.   Allow the transport of audio normalization levels as a setup
      parameter, e.g., for conference bridging.
 i.   Allow conversion to take place between media types e.g., text to
      speech and speech to text.

5.4. Signal/Event Processing and Scripting

 The Protocol must:
 a.   Allow the MGC to enable/disable monitoring for specific
      supervision events at specific circuit terminations
 b.   Allow the MGC to enable/disable monitoring for specific events
      within specified media streams
 c.   Allow reporting of detected events on the MG to the MGC. The
      protocol should provide the means to minimize the messaging
      required to report commonly-occurring event sequences.
 d.   Allow the MGC to specify other actions (besides reporting) that
      the MG should take upon detection of specified events.
 e.   Allow the MGC to enable and/or mask events.
 f.   Provide a way for MGC to positively acknowledge event
      notification.

Greene, et al. Informational [Page 9] RFC 2805 MG Control Protocol Requirements April 2000

 g.   Allow the MGC to specify signals (e.g., supervision, ringing) to
      be applied at circuit terminations.
 h.   Allow the MGC to specify content of extended duration
      (announcements, continuous tones) to be inserted into specified
      media flows.
 i.   Allow the MGC to specify alternative conditions (detection of
      specific events, timeouts) under which the insertion of
      extended-duration signals should cease.
 j.   Allow the MGC to download, and specify a script to be invoked on
      the occurrence of an event.
 k.   Specify common events and signals to maximize MG/MGC
      interworking.
 l.   Provide an extension mechanism for implementation defined events
      and signals with, for example, IANA registration procedures. It
      may be useful to have an Organizational Identifier (i.e. ITU,
      ETSI, ANSI, ) as part of the registration mechanism.
 m.   The protocol shall allow the MGC to request the arming of a
      mid-call trigger even after the call has been set up.

5.5. QoS/CoS

 The Protocol must:
 a.   Support the establishment of a bearer channel with a specified
      QoS/CoS.
 b.   Support the ability to specify QoS for the connection between
      MGs, and by direction.
 c.   Support a means to change QoS during a connection, as a whole
      and by direction.
 d.   Allow the MGC to set QOS thresholds and receive notification
      when such thresholds cannot be maintained.
 e.   Allow the jitter buffer parameters on RTP channels to be
      specified at connection setup.

Greene, et al. Informational [Page 10] RFC 2805 MG Control Protocol Requirements April 2000

5.6. Test Support

 The protocol must:
 a.   Support of the different types of PSTN Continuity Testing (COT)
      for both the originating and terminating ends of the circuit
      connection (2-wire and 4- wire).
 b.   Specifically support test line operation (e.g. 103, 105, 108).

5.7. Accounting

 The protocol must:
 a.   Support a common identifier to mark resources related to one
      connection.
 b.   Support collection of specified accounting information from MGs.
 c.   Provide the mechanism for the MGC to specify that the MG report
      accounting information automatically at end of call, in mid-call
      upon request, at specific time intervals as specified by the MGC
      and at unit usage thresholds as specified by the MGC.
 d.   Specifically support collection of:
  • start and stop time, by media flow,
  • volume of content carried (e.g. number of packets/cells

transmitted, number received with and without error, inter-

      arrival jitter), by media flow,
  • QOS statistics, by media flow.
 e.   Allow the MGC to have some control over which statistics are
      reported, to enable it to manage the amount of information
      transferred.

5.8. Signalling Control

 Establishment and provisioning of signalling backhaul channels (via
 SIGTRAN for example) is out of scope.  However, the MG must be
 capable of supporting detection of events, and application of signals
 associated with basic analogue line, and CAS type signalling.  The
 protocol must:
 a.   Support the signalling requirements of analogue lines and
      Channel Associated Signaling (CAS).

Greene, et al. Informational [Page 11] RFC 2805 MG Control Protocol Requirements April 2000

 b.   Support national variations of such signalling.
 c.   Provide mechanisms to support signalling without requiring MG-
      MGC timing constraints beyond that specified in this document.
 d.   Must not create a situation where the MGC and the MG must be
      homologated together as a mandatory requirement of using the
      protocol;
      i.e. it must be possible to optionally conceal signaling type
      variation from the MGC.

6. Resource Control

6.1. Resource Status Management

 The protocol must:
 a.   Allow the MG to report changes in status of physical entities
      supporting bearer terminations, media resources, and facility-
      associated signalling channels, due to failures, recovery, or
      administrative action. It must be able to report whether a
      termination is in service or out of service.
 b.   Support administrative blocking and release of TDM circuit
      terminations.
 Note: as the above point only relates to ISUP-controlled circuits, it
 may be unnecessary to require this since the MGC controls their use.
 However, it may be meaningful for MF and R2-signalled trunks, where
 supervisory states are set to make the trunks unavailable at the far
 end.
 c.   Provide a method for the MGC to request that the MG release all
      resources under the control of a particular MGC currently in
      use, or reserved, for any or all connections.
 d.   Provide an MG Resource Discovery mechanism which must allow an
      MGC to discover what resources the MG has. Expressing resources
      can be an arbitrarily difficult problem and the initial release
      of the protocol may have a simplistic view of resource
      discovery.
      At a minimum, resource discovery must enumerate the names of
      available circuit terminations and the allowed values for
      parameters supported by terminations.

Greene, et al. Informational [Page 12] RFC 2805 MG Control Protocol Requirements April 2000

      The protocol should be defined so that simple gateways could
      respond with a relatively short, pre-stored response to the
      discovery request mechanism. In general, if the protocol defines
      a mechanism that allows the MGC to specify a setting or
      parameter for a resource or connection in the MG, and MGs are
      not required to support all possible values for that setting or
      parameter, then the discovery mechanism should provide the MGC
      with a method to determine what possible values such settings or
      parameters are supported in a particular MG.
 e.   Provide a mechanism to discover the current available resources
      in the MG, where resources are dynamically consumed by
      connections and the MGC cannot reasonably or reliably track the
      consumption of such resources. It should also be possible to
      discover resources currently in use, in order to reconcile
      inconsistencies between the MGC and the MG.
 f.   Not require an MGC to implement an SNMP manager function in
      order to discover capabilities of an MG that may be specified
      during context establishment.

6.2. Resource Assignment

 The protocol must:
 a.   Provide a way for the MG to indicate that it was unable to
      perform a requested action because of resource exhaustion, or
      because of temporary resource unavailability.
 b.   Provide an ability for the MGC to indicate to an MG the resource
      to use for a call (e.g. DS0) exactly, or indicate a set of
      resources (e.g. pick a DS0 on a T1 line or a list of codec
      types) via a "wild card" mechanism from which the MG can select
      a specific resource for a call (e.g. the 16th timeslot, or
      G.723).
 c.   Allow the use of DNS names and IP addresses to identify MGs and
      MGCs. This shall not preclude using other identifiers for MGs or
      MGCs when other non IP transport technologies for the protocol
      are used.

7. Operational/Management Requirements

7.1. Assurance of Control/Connectivity

 To provide assurance of control and connectivity, the protocol must
 provide the means to minimize duration of loss of control due to loss
 of contact, or state mismatches.

Greene, et al. Informational [Page 13] RFC 2805 MG Control Protocol Requirements April 2000

 The protocol must:
 a.   Support detection and recovery from loss of contact due to
      failure/congestion of communication links or due to MG or MGC
      failure.
      Note that failover arrangements are one of the mechanisms which
      could be used to meet this requirement.
 b.   Support detection and recovery from loss of synchronized view of
      resource and connection states between MGCs and MGs. (e.g.
      through the use of audits).
 c.   Provide a means for MGC and MG to provide each other with
      booting and reboot indications, and what the MG's configuration
      is.
 d.   Permit more than one backup MGC and provide an orderly way for
      the MG to contact one of its backups.
 e.   Provide for an orderly switchback to the primary MGC after it
      recovers. How MGCs coordinate resources between themselves is
      outside the scope of the protocol.
 f.   Provide a mechanism so that when an MGC fails, connections
      already established can be maintained. The protocol does not
      have to provide a capability to maintain connections in the
      process of being connected, but not actually connected when the
      failure occurs.
 g.   The Protocol must allow the recovery or redistribution of
      traffic without call loss.

7.2. Error Control

 The protocol must:
 a.   Allow for the MG to report reasons for abnormal failure of lower
      layer connections e.g. TDM circuit failure, ATM VCC failure.
 b.   Allow for the MG to report Usage Parameter Control (UPC) events.
 c.   Provide means to ameliorate potential synchronization or focused
      overload of supervisory/signaling events that can be detrimental
      to either MG or MGC operation. Power restoration or signaling
      transport re-establishment are typical sources of potentially
      detrimental signaling showers from MG to MGC or vice-versa.

Greene, et al. Informational [Page 14] RFC 2805 MG Control Protocol Requirements April 2000

 d.   Allow the MG to notify the MGC that a termination was terminated
      and communicate a reason when a terminations is taken out-of-
      service unilaterally by the MG due to abnormal events.
 e.   Allow the MGC to acknowledge that a termination has been taken
      out-of-service.
 f.   Allow the MG to request the MGC to release a termination and
      communicate a reason.
 g.   Allow the MGC to specify, as a result of such a request its
      decision to take termination down, leave it as is or modify it.

7.3. MIB Requirements

 The Protocol must define a common MG MIB, which must be extensible,
 but must:
 a.   Provide information on:
  • mapping between resources and supporting physical entities.
  • statistics on quality of service on the control and signalling

backhaul interfaces.

  • statistics required for traffic engineering within the MG.
 b.   The protocol must allow the MG to provide to the MGC all
      information the MGC needs to provide in its MIB.
 c.   MG MIB must support implementation of H.341 by either the MG,
      MGC, or both acting together.

8. General Protocol Requirements

 The protocol must:
 a.   Support multiple operations to be invoked in one message and
      treated as a single transaction.
 b.   Be both modular and extensible. Not all implementations may wish
      to support all of the possible extensions for the protocol. This
      will permit lightweight implementations for specialized tasks
      where processing resources are constrained. This could be
      accomplished by defining particular profiles for particular uses
      of the protocol.

Greene, et al. Informational [Page 15] RFC 2805 MG Control Protocol Requirements April 2000

 c.   Be flexible in allocation of intelligence between MG and MGC.
      For example, an MGC may want to allow the MG to assign
      particular MG resources in some implementations, while in
      others, the MGC may want to be the one to assign MG resources
      for use.
 d.   Support scalability from very small to very large MGs: The
      protocol must support MGs with capacities ranging from one to
      millions of terminations.
 e.   Support scalability from very small to very large MGC span of
      control: The protocol should support MGCs that control from one
      MG to a few tens of thousands of MGs.
 f.   Support the needs of a residential gateway that supports one to
      a few lines, and the needs of a large PSTN gateway supporting
      tens of thousands of lines. Protocol mechanisms favoring one
      extreme or the other should be minimized in favor of more
      general purpose mechanism applicable to a wide range of MGs.
      Where special purpose mechanisms are proposed to optimize a
      subset of implementations, such mechanisms should be defined as
      optional, and should have minimal impact on the rest of the
      protocol.
 g.   Facilitate MG and MGC version upgrades independently of one
      another. The protocol must include a version identifier in the
      initial message exchange.
 h.   Facilitate the discovery of the protocol capabilities of the one
      entity to the other.
 i.   Specify commands as optional (they can be ignored) or mandatory
      (the command must be rejected), and within a command, to specify
      parameters as optional (they can be ignored) or mandatory (the
      command must be rejected).

8.1. MG-MGC Association Requirements

 The Protocol must:
 a.   Support the establishment of a control relationship between an
      MGC and an MG.
 b.   Allow multiple MGCs to send control messages to an MG. Thus, the
      protocol must allow control messages from multiple signalling
      addresses to a single MG.

Greene, et al. Informational [Page 16] RFC 2805 MG Control Protocol Requirements April 2000

 c.   Provide a method for the MG to tell an MGC that the MG received
      a command for a resource that is under the control of a
      different MGC.
 d.   Support a method for the MG to control the rate of requests it
      receives from the MGC (e.g. windowing techniques, exponential
      back-off).
 e.   Support a method for the MG to tell an MGC that it cannot handle
      any more requests.

8.2. Performance Requirements

 The protocol must:
 a.   Minimize message exchanges between MG and MGC, for example
      during boot/reboot, and during continuity tests.
 b.   Support Continuity test constraints which are a maximum of 200ms
      cross-MGC IAM (IAM is the name given to an SS7 connection setup
      msg) propagation delay, and a maximum of 200ms from end of
      dialing to IAM emission.
 c.   Make efficient use of the underlying transport mechanism. For
      example, protocol PDU sizes vs. transport MTU sizes needs to be
      considered in designing the protocol.
 d.   Not contain inherent architectural or signaling constraints that
      would prohibit peak calling rates on the order of 140
      calls/second on a moderately loaded network.
 e.   Allow for default/provisioned settings so that commands need
      only contain non-default parameters.

9. Transport

9.1. Assumptions made for underlying network

      The protocol must assume that the underlying network:
 a.   May be over large shared networks: proximity assumptions are not
      allowed.
 b.   Does not assure reliable delivery of messages.
 c.   Does not guarantee ordering of messages: Sequenced delivery of
      messages associated with the same source of events is not
      assumed.

Greene, et al. Informational [Page 17] RFC 2805 MG Control Protocol Requirements April 2000

 d.   Does not prevent duplicate transmissions.

9.2. Transport Requirements

 The protocol must:
 a.   Provide the ability to abort delivery of obsolete messages at
      the sending end if their transmission has not been successfully
      completed. For example, aborting a command that has been
      overtaken by events.
 b.   Support priority messages: The protocol shall allow a command
      precedence to allow priority messages to supercede non-priority
      messages.
 c.   Support of large fan-out at the MGC.
 d.   Provide a way for one entity to correlate commands and responses
      with the other entity.
 e.   Provide a reason for any command failure.
 f.   Provide that loss of a packet not stall messages not related to
      the message(s) contained in the packet lost.
 Note that there may be enough protocol reliability requirements here
 to warrant a separate reliable transport layer be written apart from
 the Media Gateway Control Protocol. Also need to compare Megaco
 reliable transport requirements with similar Sigtran requirements.

10. Security Requirements

 Security mechanisms may be specified as provided in underlying
 transport mechanisms, such as IPSEC.  The protocol, or such
 mechanisms, must:
 a.   Allow for mutual authentication at the start of an MGC-MG
      association
 b.   Allow for preservation of the of control messages once the
      association has been established.
 c.   Allow for optional confidentiality protection of control
      messages.  The mechanism should allow a choice in the algorithm
      to be used.
 d.   Operate across untrusted domains in a secure fashion.

Greene, et al. Informational [Page 18] RFC 2805 MG Control Protocol Requirements April 2000

 e.   Support non-repudiation for a customer-located MG talking to a
      network operator's MGC.
 f.   Define mechanisms to mitigate denial of service attacks
 Note: the protocol document will need to include an extended
 discussion of security requirements, offering more precision on each
 threat and giving a complete picture of the defense including non-
 protocol measures such as configuration.
 g.   It would be desirable for the protocol to be able to pass
      through commonly-used firewalls.

11. Requirements specific to particular bearer types

 The bearer types listed in Table 1 can be packaged into different
 types of MGs. Examples are listed in the following sections.  How
 they are packaged is outside the scope of the general Media Gateway
 control protocol. The protocol must support all types of bearer types
 listed in Table 1.

Greene, et al. Informational [Page 19] RFC 2805 MG Control Protocol Requirements April 2000

               Table 1: Bearer Types and Applications
   Bearer Type                   Applications       Transit Network
   ================================================================
   Trunk+ISUP                    trunking/access    IP, ATM, FR
                                 Voice,Fax,NAS,
                                 Multimedia
   Trunk+MF                      trunking/access    IP, ATM, FR
                                 Voice,Fax,NAS,
                                 Multimedia
   ISDN                          trunking/access    IP, ATM, FR
                                 Voice,Fax,NAS,
                                 Multimedia
   Analogue                      Voice,Fax,         IP, ATM, FR
                                 Text Telephony
   Termination in a Restricted   Voice,Fax,         IP, ATM, FR
   Capability Gateway            Text Telephony
   Application Termination       IVR,ARF, Announcement Server,
                                 Voice Recognition Server,...
   Multimedia H.323              H.323 Multimedia   IP, ATM, FR
                                 Gateway and MCU
   Multimedia H.320              H.323 GW and MCU   ISDN, IP, ATM, FR

11.1. Media-specific Bearer Types

 This section describes requirements for handling terminations
 attached to specific types of networks.

11.1.1. Requirements for TDM PSTN (Circuit)

 This bearer type is applicable to a Trunking GW, Access GW, ...
 The protocol must allow:
 a.   the MGC to specify the encoding to use on the attached circuit.
 b.   In general, if something is set by a global signalling protocol
      (e.g. ISUP allows mu-Law or A-Law to be signaled using ISUP)
      then it must be settable by the protocol.

Greene, et al. Informational [Page 20] RFC 2805 MG Control Protocol Requirements April 2000

 c.   TDM attributes:
  • Echo cancellation,
  • PCM encoding or other voice compression (e.g. mu-law or A-law),
  • encryption,
  • rate adaptation (e.g. V.110, or V.120).
 d.   for incoming calls, identification of a specific TDM circuit
      (timeslot and facility).
 e.   for calls outgoing to the circuit network, identification of a
      specific circuit or identification of a circuit group with the
      indication that the MG must select and return the identification
      of an available member of that group.
 f.   specification of the default encoding of content passing to and
      from a given circuit, possibly on a logical or physical circuit
      group basis.
 g.   specification at any point during the life of a connection of
      variable aspects of the content encoding, particularly including
      channel information capacity.
 h.   specification at any point during the life of a connection of
      loss padding to be applied to incoming and outgoing media
      streams at the circuit termination.
 i.   specification at any point during the life of a connection of
      the applicability of echo cancellation to the outgoing media
      stream.
 j.   Multi-rate calls to/from the SCN.
 k.   H-channel (n x 64K) calls to/from the SCN.
 l.   B channel aggregation protocols for creating high speed channels
      for multimedia over the SCN.
 m.   Modem terminations and negotiations.
 The protocol may also allow:
 n.   specification of sub-channel media streams,
 o.   specification of multi-channel media streams.

Greene, et al. Informational [Page 21] RFC 2805 MG Control Protocol Requirements April 2000

11.1.2. Packet Bearer Type

 The protocol must be able to specify:
 a.   ingress and egress coding (i.e. the way packets coming in and
      out are encoded) (including encryption).
 b.   near and far-end ports and other session parameters for RTP and
      RTCP.
 The protocol must support reporting of:
 c.   re-negotiation of codec for cause - for further study
 d.   on Trunking and Access Gateways, resources capable of more than
      one active connection at a time must also be capable of mixing
      and packet duplication.
 The protocol must allow:
 e.   specification of parameters for outgoing and incoming packet
      flows at separate points in the life of the connection (because
      far-end port addresses are typically obtained through a separate
      signalling exchange before or after the near-end port addresses
      are assigned).
 f.   the possibility for each Media Gateway to allocate the ports on
      which it will receive packet flows (including RTCP as well as
      media streams) and report its allocations to the Media Gateway
      Controller for signalling to the far end.  Note that support of
      different IP backbone providers on a per call basis would
      require that the ports on which packets flow be selected by the
      MGC. (but only if the IP address of the MG is different for each
      backbone provider).
 g.   the specification at any point during the life of a connection
      of RTP payload type and RTP session number for each RTP-
      encapsulated media flow.
 h.   the ability to specify whether outgoing flows are to be uni-cast
      or multi-cast. Note that on an IP network this information is
      implicit in the destination address, but in other networks this
      is a connection parameter.
 i.   invoking of encryption/decryption on media flows and
      specification of the associated algorithm and key.

Greene, et al. Informational [Page 22] RFC 2805 MG Control Protocol Requirements April 2000

 The protocol should also allow:
 j.   the MGC to configure non-RTP (proprietary or other) encapsulated
      packet flows.

11.1.3. Bearer type requirements for ATM

 This bearer type is applicable to Trunking GW, Access GW, ....

11.1.3.1. Addressing

 a.   The protocol must be able to specify the following termination
      attributes:
  • VC identifier,
  • VC identifier plus AAL2 slot, and variant of these allowing the

gateway to choose (part of) the identifier,

  • remote termination network address, remote MG name.
 b.   Allow specification of an ATM termination which is to be
      assigned to an MG connection as a VC identifier, a VC identifier
      plus AAL2 slot, a wild-carded variant of either of these. A
      remote termination network address, or a remote MG name could
      also be used when the MG can select the VC and change the VC
      during the life of the connection by using ATM signalling.
 c.   Provide an indication by the MG of the VC identifier and
      possibly AAL2 slot of the termination actually assigned to a
      connection.
 d.   Provide a means to refer subsequently to that termination.
 e.   Refer to an existing VCC as the physical interface + Virtual
      Path Identifier (VPI) + Virtual Circuit Identifier (VCI).
 f.   Where the VCC is locally established (SVCs signalled by the
      Gateway through UNI or PNNI signalling or similar), the VCC must
      be indirectly referred to in terms which are of significance to
      both ends of the VCC. For example, a global name or the ATM
      address of the ATM devices at each end of the VCC. However, it
      is possible/probable that there may be several VCCs between a
      given pair of ATM devices. Therefore the ATM address pair must
      be further resolved by a VCC identifier unambiguous within the
      context of the ATM address pair.
 g.   refer to a VCC as the Remote GW ATM End System Address + VCCI.

Greene, et al. Informational [Page 23] RFC 2805 MG Control Protocol Requirements April 2000

 h.   allow the VCCI to be selected by the MG or imposed on the MG.
 i.   support all ATM addressing variants (e.g. ATM End System Address
      (AESA) and E.164).

11.1.3.2. Connection related requirements

 The protocol must:
 a.   Allow for the de-coupling of creation/deletion of the narrow-
      band connection from the creation/deletion of the underlying
      VCC.
 b.   Allow for efficient disconnection of all connections associated
      with a physical port or VCC. As an example, this could aggregate
      disconnections across a broadband circuit which experienced a
      physical error.
 c.   Allow the connection established using this protocol to be
      carried over a VCC, which may be a:
  • PVC or SPVC,
  • an SVC established on demand, either by the MGC itself or by a

broker acting on its behalf or,

  • an SVC originated as required by the local MG, or by the remote

end to the local MG through UNI or PNNI signalling.

 d.   Allow ATM transport parameters and QoS parameters to be passed
      to the MG.
 e.   Allow blocking and unblocking of a physical interface, a VCC or
      an AAL1/AAL2 channel.
 The protocol should:
 f.   Where a VCC is required to be established on a per narrow-band
      call basis, allow all necessary information to be passed in one
      message.

11.1.3.3. Media adaptation

 The protocol must:
 a.   Allow AAL parameters to be passed to the MG.

Greene, et al. Informational [Page 24] RFC 2805 MG Control Protocol Requirements April 2000

 b.   Allow AAL1/AAL2 multiple narrow-band calls to be mapped to a
      single VCC. For AAL2, these calls are differentiated within each
      VCC by a AAL2 channel identifier. An AAL2 connection may span
      more than 1 VCC and transit AAL2 switching devices.  ITU
      Q.2630.1 [2] defines an end-to-end identifier called the Served
      User Generated Reference (SUGR). It carries information from the
      originating user of the AAL2 signalling protocol to the
      terminating user transparently and unmodified.
 c.   Allow unambiguous binding of a narrow band call to an AAL2
      connection identifier, or AAL1 channel, within the specified
      VCC.
 d.   Allow the AAL2 connection identifier, or AAL1 channel, to be
      selected by the MG or imposed on the MG.
 e.   Allow the use of the AAL2 channel identifier (cid) instead of
      the AAL2 connection identifier.
 f.   Allow the AAL2 voice profile to be imposed or negotiated before
      the start of the connection.  AAL2 allows for variable length
      packets and varying packet rates, with multiple codecs possible
      within a given profile. Thus a given call may upgrade or
      downgrade the codec within the lifetime of the call. Idle
      channels may generate zero bandwidth. Thus an AAL2 VCC may vary
      in bandwidth and possibly exceed its contract. Congestion
      controls within a gateway may react to congestion by modifying
      codec rates/types.
 g.   Allow the MGC to instruct the MG on how individual narrow-band
      calls behave under congestion.
 h.   Allow for the MGC to specify an AAL5 bearer, with the following
      choices:
  • Per ATM Forum standard AF-VTOA-0083 [4],
  • RTP with IP/UDP,
  • RTP without IP/IDP per H.323v2 Annex C [5],
  • Compressed RTP per ATM Forum AF-SAA-0124.000 [6].
 i.   Allow unambiguous binding of a narrow band call to an AAL1
      channel within the specified VCC. (In AAL1, multiple narrow-band
      calls may be mapped to a single VCC.)

Greene, et al. Informational [Page 25] RFC 2805 MG Control Protocol Requirements April 2000

11.1.3.4. Reporting requirements

 The protocol should:
 a.   Allow any end-of-call statistics to show loss/restoration of
      underlying VCC within the calls duration, together with duration
      of loss.
 b.   Allow notification, as requested by MGC, of any congestion
      avoidance actions taken by the MG.
 The protocol must:
 c.   Allow for ATM VCCs or AAL2 channels to be audited by the MGC.
 d.   Allow changes in status of ATM VCCs or AAL2 channels to be
      notified as requested by the MGC.
 e.   Allow the MGC to query the resource and endpoint availability.
      Resources may include VCCs, and DSPs. VCCs may be up or down.
      End-points may be connection-free, connected or unavailable.

11.1.3.5. Functional requirements

 The protocol must:
 a.   Allow an MGC to reserve a bearer, and specify a route for it
      through the network.

11.2. Application-Specific Requirements

11.2.1. Trunking Gateway

 A Trunking Gateway is an interface between SCN networks and Voice
 over IP or Voice over ATM networks.  Such gateways typically
 interface to SS7 or other NNI signalling on the SCN and manage a
 large number of digital circuits.
 The protocol must:
 a.   Provide circuit and packet-side loopback.
 b.   Provide circuit-side n x 64kbs connections.
 c.   Provide subrate and multirate connections for further study.

Greene, et al. Informational [Page 26] RFC 2805 MG Control Protocol Requirements April 2000

 d.   Provide the capability to support Reporting/generation of
      per-trunk CAS signalling (DP, DTMF, MF, R2, J2, and national
      variants).
 e.   Provide the capability to support reporting of detected DTMF
      events either digit-by-digit, as a sequence of detected digits
      with a flexible mechanism For the MG to determine the likely end
      of dial string, or in a separate RTP stream.
 f.   Provide the capability to support ANI and DNIS generation and
      reception.

11.2.2. Access Gateway

 An Access Gateway connects UNI interfaces like ISDN (PRI and BRI) or
 traditional analog voice terminal interfaces, to a Voice over IP or
 Voice over ATM network, or Voice over Frame Relay network.
 The Protocol must:
 a.   Support detection and generation of analog line signaling
      (hook-state, ring generation).
 b.   Provide the capability to support reporting of detected DTMF
      events either digit-by-digit, as a sequence of detected digits
      with a flexible mechanism For the MG to determine the likely end
      of dial string, or in a separate RTP stream.
 c.   Not require scripting mechanisms, event buffering, digit map
      storage when implementing restricted function (1-2 line)
      gateways with very limited capabilities.
 d.   Provide the capability to support CallerID generation and
      reception.
 Proxying of the protocol is for further study.

11.2.3. Trunking/Access Gateway with fax ports

 a.   the protocol must be able to indicate detection of fax media.
 b.   the protocol must be able to specify T.38 for the transport of
      the fax.
 c.   the protocol must be able to specify G.711 encoding for
      transport of fax tones across a packet network.

Greene, et al. Informational [Page 27] RFC 2805 MG Control Protocol Requirements April 2000

11.2.4. Trunking/Access Gateway with text telephone access ports

 An access gateway with ports capable of text telephone communication,
 must provide communication between text telephones in the SCN and
 text conversation channels in the packet network.
 Text telephone capability of ports is assumed to be possible to
 combine with other options for calls as described in section 11.2.6
 (e.) on "Adaptable NASes".
 The port is assumed to adjust for the differences in the supported
 text telephone protocols, so that the text media stream can be
 communicated T.140 coded in the packet network without further
 transcoding [7].
 The protocol must be capable of reporting the type of text telephone
 that is connected to the SCN port. The foreseen types are the same as
 the ones supported by ITU-T V.18:  DTMF, EDT, Baudot-45, Baudot-50,
 Bell, V.21, Minitel and V.18. It should be possible to control which
 protocols are supported. The SCN port is assumed to contain ITU-T
 V.18 functionality [8].
 The protocol must be able to control the following functionality
 levels of text telephone support:
 a.   Simple text-only support: The call is set into text mode from
      the beginning of the call, in order to conduct a text-only
      conversation.
 b.   Alternating text-voice support: The call may begin in voice mode
      or text mode and, at any moment during the call, change mode on
      request by the SCN user. On the packet side, the two media
      streams for voice and text must be opened, and it must be
      possible to control the feeding of each stream by the protocol.
 c.   Simultaneous text and voice support: The call is performed in a
      mode when simultaneous text and voice streams are supported. The
      call may start in voice mode and during the call change state to
      a text-and-voice call.
 A port may implement only level a, or any level combination of a, b
 and c, always including level a.
 The protocol must support:
 d.   A text based alternative to the interactive voice response, or
      audio resource functionality of the gateway when the port is
      used in text telephone mode.

Greene, et al. Informational [Page 28] RFC 2805 MG Control Protocol Requirements April 2000

 e.   Selection of what national translation table to be used between
      the Unicode based T.140 and the 5-7 bit based text telephone
      protocols.
 f.   Control of the V.18 probe message to be used on incoming calls.

11.2.5. Network Access Server

 A NAS is an access gateway, or Media Gateway (MG), which terminates
 modem signals or synchronous HDLC connections from a network (e.g.
 SCN or xDSL network) and provides data access to the packet network.
 Only those requirements specific to a NAS are described here.
 Figure 1 provides a reference architecture for a Network Access
 Server (NAS). Signaling comes into the MGC and the MGC controls the
 NAS.
                        +-------+        +-------+
             Signaling  |       |        |       |
             -----------+  MGC  +        |  AAA  |
                        |       |        |       |
                        +---+---+        +--+----+
                            |               |
                      Megaco|_______________|
                                            |
                                            |
                        +---+---+         ~~|~~~
              Bearer    |       |        (      )
             -----------+  NAS  +-------(   IP   )
                        |       |        (      )
                        +-------+         ~~~~~~
                Figure 1: NAS reference architecture
 The Protocol must support:
 a.   Callback capabilities:
  • Callback
 b.   Modem calls.  The protocol must be able to specify the modem
      type(s) to be used for the call.
 c.   Carriage of bearer information.  The protocol must be able to
      specify the data rate of the TDM connection (e.g., 64 kbit/s, 56
      kbit/s, 384 kbit/s), if this is available from the SCN.

Greene, et al. Informational [Page 29] RFC 2805 MG Control Protocol Requirements April 2000

 d.   Rate Adaptation: The protocol must be able to specify the type
      of rate adaptation to be used for the call including indicating
      the subrate, if this is available from the SCN (e.g. 56K, or
      V.110 signaled in Bearer capabilities with subrate connection of
      19.2kbit/s).
 e.   Adaptable NASes: The protocol must be able to support multiple
      options for an incoming call to allow the NAS to dynamically
      select the proper type of call.  For example, an incoming ISDN
      call coded for "Speech" Bearer Capability could actually be a
      voice, modem, fax, text telephone, or 56 kbit/s synchronous
      call.  The protocol should allow the NAS to report back to the
      MGC the actual type of call once it is detected.
 The 4 basic types of bearer for a NAS are:
 1.   Circuit Mode, 64-kbps, 8-khz structured, Speech
 2.   Circuit Mode, 64-kbps, 8-khz structured, 3.1-khz, Audio
 3.   Circuit Mode, 64-kbps, 8-khz structured, Unrestricted Digital
      Transmission-Rate Adapted from 56-kbps
 4.   Circuit Mode, 64-kbps, 8-khz structure, Unrestricted Digital
      Transmission
 f.   Passage of Called and Calling Party Number information to the
      NAS from the MGC. Also, passage of Charge Number/Billing Number,
      Redirecting Number, and Original Call Number, if known, to the
      NAS from the MGC. If there are other Q.931 fields that need to
      be passed from the MGC to the MG, then it should be possible to
      pass them [9].
 g.   Ability for the MGC to direct the NAS to connect to a specific
      tunnel, for example to an LNS, or to an AAA server.
 h.   When asked by the MGC, be able to report capability information,
      for example, connection types (V.34/V90/Synch ISDN..), AAA
      mechanism (RADIUS/DIAMETER/..), access type (PPP/SLIP/..) after
      restart or upgrade.

11.2.6. Restricted Capability Gateway

 The requirements here may also be applied to small analog gateways,
 and to cable/xDSL modems. See also the section on access gateways.

Greene, et al. Informational [Page 30] RFC 2805 MG Control Protocol Requirements April 2000

 The Protocol must support:
 a.   The ability to provide a scaled down version of the protocol.
      When features of the protocol are not supported, an appropriate
      error message must be sent. Appropriate default action must be
      defined.  Where this is defined may be outside the scope of the
      protocol.
 b.   The ability to provide device capability information to the MGC
      with respect to the use of the protocol.

11.2.7. Multimedia Gateway

 The protocol must have sufficient capability to support a multimedia
 gateway. H.320 and H.324 are characterized by a single data stream
 with multiple media streams multiplexed on it.
 If the mapping is from H.320 or H.324 on the circuit side, and H.323
 on the packet side, it is assumed that the MG knows how to map
 respective subchannels from H.320/H.324 side to streams on packet
 side. If extra information is required when connecting two
 terminations, then it must be supplied so that the connections are
 not ambiguous.
 The Multimedia Gateway:
 1)   should support Bonding Bearer channel aggregation,
 2)   must support 2xB (and possibly higher rates) aggregation via
      H.221,
 3)   must be able to dynamically change the size of audio, video and
      data channels within the h.320 multiplex,
 4)   must react to changes in the H.320 multiplex on 20 msec
      boundaries,
 5)   must support TCS4/IIS BAS commands,
 6)   must support detection and creation of DTMF tones,
 7)   should support SNMP MIBS as specified in H.341 [3]
 a.   If some of the above cannot be handled by the MGC to MG protocol
      due to timing constraints, then it is likely that the H.245 to
      H.242 processing must take place in the MG. Otherwise, support
      for this functionality in the multimedia gateway are protocol
      requirements.

Greene, et al. Informational [Page 31] RFC 2805 MG Control Protocol Requirements April 2000

 b.   It must be possible on a call by call basis for the protocol to
      specify different applications. Thus, one call might be PSTN to
      PSTN under SS7 control, while the next might be ISDN/H.320 under
      SS7 control to H.323.  This is only one example; the key
      requirement is that the protocol not prevent such applications.

11.2.8. Audio Resource Function

 An Audio Resource Function (ARF) consists of one or more functional
 modules which can be deployed on an stand alone media gateway server
 IVR, Intelligent Peripheral, speech/speaker recognition unit, etc. or
 a traditional media gateway.  Such a media gateway is known as an
 Audio Enabled Gateway (AEG) if it performs tasks defined in one or
 more of the following ARF functional modules:
                 Play Audio,
                 DTMF Collect,
                 Record Audio,
                 Speech Recognition,
                 Speaker Verification/Identification,
                 Auditory Feature Extraction/Recognition, or
                 Audio Conferencing.
 Additional ARF function modules that support human to machine
 communications through the use of telephony tones (e.g., DTMF) or
 auditory means (e.g.  speech) may be appended to the AEG definition
 in future versions of these requirements.
 Generic scripting packages for any module must support all the
 requirements for that module. Any package extension for a given
 module must include, by inheritance or explicit reference, the
 requirements for that given module.
 The protocol requirements for each of the ARF modules are provided in
 the following subsections.

11.2.8.1. Play Audio Module

 a.   Be able to provide the following basic operation:
  1. request an ARF MG to play an announcement.
 b.   Be able to specify these play characteristics:
  1. Play volume
  1. Play speed

Greene, et al. Informational [Page 32] RFC 2805 MG Control Protocol Requirements April 2000

  1. Play iterations
  1. Interval between play iterations
  1. Play duration
 c.   Permit the specification of voice variables such as DN, number,
      date, time, etc.  The protocol must allow specification of both
      the value (eg 234-3456), and well as the type (Directory
      number).
 d.   Using the terminology that a segment is a unit of playable
      speech, or is an abstraction that is resolvable to a unit of
      playable speech, permit specification of the following segment
      types:
  1. A provisioned recording.
  1. A block of text to be converted to speech.
  1. A block of text to be displayed on a device.
  1. A length of silence qualified by duration.
  1. An algorithmically generated tone.
  1. A voice variable, specified by type and value. Given a variable

type and value, the IVR/ARF unit would dynamically assemble the

      phrases required for its playback.
  1. An abstraction that represents a sequence of audio segments.

Nesting of these abstractions must also be permitted.

 An example of this abstraction is a sequence of audio segments, the
 first of which is a recording of the words "The number you have
 dialed", followed by a Directory Number variable, followed by a
 recording of the words "is no longer in service".
  1. An abstraction that represents a set of audio segments and which

is resolved to a single segment by a qualifier. Nesting of

      these abstractions must be permitted.
 For example take a set of audio segments recorded in different
 languages all of which express the semantic concept "The number you
 have dialed is no longer in service".  The set is resolved by a
 language qualifier. If the qualifier is "French", the set resolves to
 the French version of this announcement.

Greene, et al. Informational [Page 33] RFC 2805 MG Control Protocol Requirements April 2000

 In the case of a nested abstraction consisting of a set qualified by
 language at one level and and a set qualified by gender at another
 level,  it would be possible to specify that an announcement be
 played in French  and spoken by a female voice.
 e.   Provide two different methods of audio specification:
  1. Direct specification of the audio components to be played by

specifying the sequence of segments in the command itself.

  1. Indirect specification of the audio components to be played by

reference to a single identifier that resolves to a provisioned

      sequence of audio segments.

11.2.8.2. DTMF Collect Module

 The DTMF Collect Module must support all of the requirements in the
 Play Module in addition to the following requirements:
 a.   Be able to provide the following basic operation:
  1. request an AEG to play an announcement, which may optionally

terminated by DTMF, and then collect DTMF

 b.   Be able to specify these event collection characteristics:
  1. The number of attempts to give the user to enter a valid DTMF

pattern.

 c.   With respect to digit timers, allow the specification of:
  1. Time allowed to enter the first digit.
  1. Time allowed for user to enter each digit subsequent to the

first digit.

  1. Time allowed for user to enter a digit once the maximum expected

number of digits has been entered.

 d.   To be able to allow multiple prompt operations DTMF digit
      collection, voice recording (if supported), and/or speech
      recognition analysis (if supported) provide the following types
      of prompts:
  1. Initial Prompt
  1. Reprompt

Greene, et al. Informational [Page 34] RFC 2805 MG Control Protocol Requirements April 2000

  1. Error prompt
  1. Failure announcement
  1. Success announcement.
 e.   To allow digit pattern matching, allow the specification of:
  1. maximum number of digits to collect.
  1. minimum number of digits to collect.
  1. a digit pattern using a regular expression.
 f.   To allow digit buffer control, allow the specification of:
  1. Ability to clear digit buffer prior to playing initial prompt

(default is not to clear buffer).

  1. Default clearing of buffer following playing of un-interruptible

announcement segment.

  1. Default clearing of buffer before playing a re-prompt in

response to previous invalid input.

 g.   Provide a method to specify DTMF interruptibility on a per audio
      segment basis.
 h.   Allow the specification of definable key sequences for DTMF
      digit collection to:
  1. Discard collected digits in progress, replay the prompt, and

resume DTMF digit collection.

  1. Discard collected digits in progress and resume DTMF digit

collection.

  1. Terminate the current operation and return the terminating key

sequence to the MGC.

 i.   Provide a way to ask the ARF MG to support the following
      definable keys for digit collection and recording. These keys
      would then be able to be acted upon by the ARF MG:
  1. A key to terminate playing of an announcement in progress.
  1. A set of one or more keys that can be accepted as the first

digit to be collected.

Greene, et al. Informational [Page 35] RFC 2805 MG Control Protocol Requirements April 2000

  1. A key that signals the end of user input. The key may or may

not be returned to the MGC along with the input already

      collected.
  1. Keys to stop playing the current announcement and resume playing

at the beginning of the first segment of the announcement, last

      segment of the announcement, previous segment of the
      announcement, next segment of the announcement, or the current
      announcement segment.

11.2.8.3. Record Audio Module

 The Record Module must support all of the requirements in the Play
 Module as in addition to the following requirements:
 a.   Be able to provide the following basic operation:
  1. request an AEG to play an announcement and then record voice.
 b.   Be able to specify these event collection characteristics:
  1. The number of attempts to give the user to make a recording.
 c.   With respect to recording timers, allow the specification of:
  1. Time to wait for the user to initially speak.
  1. The amount of silence necessary following the last speech

segment for the recording to be considered complete.

  1. The maximum allowable length of the recording (not including

pre- and post- speech silence).

 d.   To be able to allow multiple prompt operations for DTMF digit
      collection (if supported), voice recording (if supported),
      speech recognition analysis (if supported) and/or speech
      verification/identification (if supported) and then to provide
      the following types of prompts:
  1. Initial Prompt
  1. Reprompt
  1. Error prompt
  1. Failure announcement
  1. Success announcement.

Greene, et al. Informational [Page 36] RFC 2805 MG Control Protocol Requirements April 2000

 e.   Allow the specification of definable key sequences for digit
      recording or speech recognition analysis (if supported) to:
  1. Discard recording in progress, replay the prompt, and resume

recording.

  1. Discard recording in progress and resume recording.
  1. Terminate the current operation and return the terminating key

sequence to the MGC.

 f.   Provide a way to ask the ARF MG to support the following
      definable keys for recording. These keys would then be able to
      be acted upon by the ARF MG:
  1. A key to terminate playing of an announcement in progress.
  1. A key that signals the end of user input. The key may or may

not be returned to the MGC along with the input already

      collected.
  1. Keys to stop playing the current announcement and resume playing

at the beginning of the first segment of the announcement, last

      segment of the announcement, previous segment of the
      announcement, next segment of the announcement, or the current
      announcement segment.
 g.   While audio prompts are usually provisioned in IVR/ARF MGs,
      support changing the provisioned prompts in a voice session
      rather than a data session.  In particular, with respect to
      audio management:
  1. A method to replace provisioned audio with audio recorded during

a call. The newly recorded audio must be accessible using the

      identifier of the audio it replaces.
  1. A method to revert from replaced audio to the original

provisioned audio.

  1. A method to take audio recorded during a call and store it such

that it is accessible to the current call only through its own

      newly created unique identifier.
  1. A method to take audio recorded during a call and store it such

that it is accessible to any subsequent call through its own

      newly created identifier.

Greene, et al. Informational [Page 37] RFC 2805 MG Control Protocol Requirements April 2000

11.2.8.4. Speech Recognition Module

 The speech recognition module can be used for a number of speech
 recognition applications, such as:
  1. Limited Vocabulary Isolated Speech Recognition (e.g., "yes",

"no", the number "four"),

  1. Limited Vocabulary Continuous Speech Feature Recognition (e.g.,

the utterance "four hundred twenty-three dollars"),and/or

  1. Continuous Speech Recognition (e.g., unconstrained speech

recognition tasks).

 The Speech Recognition Module must support all of the requirements in
 the Play Module as in addition to the following requirements:
 a.   Be able to provide the following basic operation: request an AEG
      to play an announcement and then perform speech recognition
      analysis.
 b.   Be able to specify these event collection characteristics:
  1. The number of attempts to give to perform speech recognition

task.

 c.   With respect to speech recognition analysis timers, allow the
      specification of:
  1. Time to wait for the user to initially speak.
  1. The amount of silence necessary following the last speech

segment for the speech recognition analysis segment to be

      considered complete.
  1. The maximum allowable length of the speech recognition analysis

(not including pre- and post- speech silence).

 d.   To be able to allow multiple prompt operations for DTMF digit
      collection  (if supported), voice recording (if supported),
      and/or speech recognition analysis and then to provide the
      following types of prompts:
  1. Initial Prompt
  1. Reprompt
  1. Error prompt

Greene, et al. Informational [Page 38] RFC 2805 MG Control Protocol Requirements April 2000

  1. Failure announcement
  1. Success announcement.
 e.   Allow the specification of definable key sequences for digit
      recording (if supported) or speech recognition analysis to:
  1. Discard in process analysis, replay the prompt, and resume

analysis.

  1. Discard recording in progress and resume analysis.
  1. Terminate the current operation and return the terminating key

sequence to the MGC.

 f.   Provide a way to ask the ARF MG to support the following
      definable keys for speech recognition analysis. These keys would
      then be able to be acted upon by the ARF MG:
  1. A key to terminate playing of an announcement in progress.
  1. A key that signals the end of user input. The key may or may

not be returned to the MGC along with the input already

      collected.
  1. Keys to stop playing the current announcement and resume playing

at the beginning of the first segment of the announcement, last

      segment of the announcement, previous segment of the
      announcement, next segment of the announcement, or the current
      announcement segment.

11.2.8.5. Speaker Verification/Identification Module

 The speech verification/identification module returns parameters that
 indicate either the likelihood of the speaker to be the person that
 they claim to be (verification task) or the likelihood of the speaker
 being one of the persons contained in a set of previously
 characterized speakers (identification task).
 The Speaker Verification/Identification Module must support all of
 the requirements in the Play Module in addition to the following
 requirements:
 a.   Be able to download parameters, such as speaker templates
      (verification task) or sets of potential speaker templates
      (identification task), either prior to the session or in mid-
      session.

Greene, et al. Informational [Page 39] RFC 2805 MG Control Protocol Requirements April 2000

 b.   Be able to download application specific software to the ARF
      either prior to the session or in mid-session.
 c.   Be able to return parameters indicating either the likelihood of
      the speaker to be the person that they claim to be (verification
      task) or the likelihood of the speaker being one of the persons
      contained in a set of previously characterized speakers
      (identification task).
 d.   Be able to provide the following basic operation: request an AEG
      to play an announcement and then perform speech
      verification/identification analysis.
 e.   Be able to specify these event collection characteristics: The
      number of attempts to give to perform speech
      verification/identification task.
 f.   With respect to speech verification/identification analysis
      timers, allow the specification of:
  1. Time to wait for the user to initially speak.
  1. The amount of silence necessary following the last speech

segment for the speech verification/identification analysis

      segment to be considered complete.
  1. The maximum allowable length of the speech

verification/identification analysis (not including pre- and

      post- speech silence).
 g.   To be able to allow multiple prompt operations for DTMF digit
      collection (if supported), voice recording, (if supported),
      speech recognition analysis (if supported) and/or speech
      verification/identification and provide the following types of
      prompts:
  1. Initial Prompt
  1. Reprompt
  1. Error prompt
  1. Failure announcement
  1. Success announcement.

Greene, et al. Informational [Page 40] RFC 2805 MG Control Protocol Requirements April 2000

 h.   Allow the specification of definable key sequences for digit
      recording (if supported) or speech recognition (if supported) in
      the speech verification/identification analysis to:
  1. Discard speech verification/identification in analysis, replay

the prompt, and resume analysis.

  1. Discard speech verification/identification analysis in progress

and resume analysis.

  1. Terminate the current operation and return the terminating key

sequence to the MGC.

 i.   Provide a way to ask the ARF MG to support the following
      definable keys for speech verification/identification analysis.
      These keys would then be able to be acted upon by the ARF MG:
  1. A key to terminate playing of an announcement in progress.
  1. A key that signals the end of user input. The key may or may

not be returned to the MGC along with the input already

      collected.
  1. Keys to stop playing the current announcement and resume speech

verification/identification at the beginning of the first

      segment of the announcement, last segment of the announcement,
      previous segment of the announcement, next segment of the
      announcement, or the current announcement segment.

11.2.8.6. Auditory Feature Extraction/Recognition Module

 The auditory feature extraction/recognition module is engineered to
 continuously monitor the auditory stream for the appearance of
 particular auditory signals or speech utterances of interest and to
 report these events (and optionally a signal feature representation
 of these events) to network servers or MGCs.
 The Auditory Feature Extraction/Recognition Module must support the
 following requirements:
 a.   Be able to download application specific software to the ARF
      either prior to the session or in mid-session.
 b.   Be able to download parameters, such as a representation of the
      auditory feature to extract/recognize, for prior to the session
      or in mid-session.

Greene, et al. Informational [Page 41] RFC 2805 MG Control Protocol Requirements April 2000

 c.   Be able to return parameters indicating the auditory event found
      or a representation of the feature found (i.e., auditory
      feature).

11.2.8.7. Audio Conferencing Module

 The protocol must support:
 a.   a mechanism to create multi-point conferences of audio only and
      multimedia conferences in the MG.
 b.   audio mixing; mixing multiple audio streams into a new composite
      audio stream
 c.   audio switching; selection of incoming audio stream to be sent
      out to all conference participants.

11.2.9. Multipoint Control Units

 The protocol must support:
 a.   a mechanism to create multi-point conferences of audio only and
      multimedia conferences in the MG.
 b.   audio mixing; mixing multiple audio streams into a new composite
      audio stream
 c.   audio switching; selection of incoming audio stream to be sent
      out to all conference participants.
 d.   video switching; selection of video stream to be sent out to all
      conference participants
 e.   lecture video mode; a video selection option where on video
      source is sent out to all conference users
 f.   multi-point of T.120 data conferencing.
 g.   The ability for the MG to function as an H.323 MP, and for the
      MGC to function as an H.323 MC, connected by this protocol
      (MEGACOP/H.248).  It should be possible for audio, data, and
      video MG/MPs to be physically separate while being under the
      control of a single MGC/H.323 MC.

Greene, et al. Informational [Page 42] RFC 2805 MG Control Protocol Requirements April 2000

12. References

 [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [2]  ITU-T Recommendation Q.2630.1, AAL type 2 Signalling Protocol
      (Capability Set 1), December 1999.
 [3]  ITU-T Recommendation H.341, Line Transmission of Non-Telephone
      Signals, May 1999.
 [4]  ATM Forum Technical Committee, af-vtoa-0083.001, Voice and
      Telephony Over ATM to the Desktop Specification, March 1999.
 [5]  ITU-T Recommendation H.323v3, Packet-based Multimedia
      Communications Systems (includes Annex C - H.323 on ATM),
      September 1999.
 [6]  ATM Forum Technical Committee, af-saa-0124.000, Gateway for
      H.323 Media Transport Over ATM, May 1999.
 [7]  ITU-T Recommendation T.140, Protocol for Multimedia Application
      Text Conversation, February 1998.
 [8]  ITU-T Recommendation V.18, Operational and Interworking
      Requirements for DCEs Operating in Text Telephone Mode, February
      1998.
 [9]  ITU-T Recommendation Q.931, Digital Subscriber Signalling System
      No. 1 (DSS 1) - ISDN User - Network Interface Layer 3
      Specification for Basic Call Control, May 1998.

14. Acknowledgements

 The authors would like to acknowledge the many contributors who
 debated the Media Gateway Control Architecture and Requirements on
 the IETF Megaco and Sigtran mailing lists. Contributions to this
 document have also been made through internet-drafts and discussion
 with members of ETSI Tiphon, ITU-T SG16, TIA TR41.3.4, the ATM Forum,
 and the Multiservice Switching Forum.

Greene, et al. Informational [Page 43] RFC 2805 MG Control Protocol Requirements April 2000

15. Authors' Addresses

 Nancy Greene
 Nortel Networks
 P.O. Box 3511 Stn C
 Ottawa, ON, Canada K1Y 4H7
 Phone: (514) 271-7221
 EMail: ngreene@nortelnetworks.com
 Michael A. Ramalho
 Cisco Systems
 1802 Rue de la Port
 Wall Township, NJ
 Phone: +1.732.449.5762
 EMail: mramalho@cisco.com
 Brian Rosen
 Marconi
 1000 FORE Drive, Warrendale, PA 15086
 Phone: (724) 742-6826
 EMail: brosen@eng.fore.com

Greene, et al. Informational [Page 44] RFC 2805 MG Control Protocol Requirements April 2000

16. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

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

Greene, et al. Informational [Page 45]

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