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

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.

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

        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

   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

        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

        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".

   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".

   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".

   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

   (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

   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.

          +------------------------------------------------------+
          |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

   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

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

   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.

   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.

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,

   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.

   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.

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.

   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_.}.

   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

   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.

   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.

   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

   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:

   (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.

    .  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.

   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.

   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

   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

   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).

   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

    . 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).

   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"

   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

      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

   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.

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

       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).

   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

              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.

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.

   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

   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.

   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.

   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

   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]

   [,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.

   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:

   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

   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

   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

        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.

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

        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.

       +----------------------------------------------------------+
       | 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

   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.

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.

   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

   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

   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

      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

   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

   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

   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

   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.

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.

   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

   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).

   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

       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.

    .  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

         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.

   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.

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.

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.

   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

   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
   {

        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,
        ...
   }

   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)

   -- Context NULL Value: 0
   -- Context CHOOSE Value: 429467294 (0xFFFFFFFE)
   -- Context ALL Value: 4294967295 (0xFFFFFFFF)

   ActionRequest ::= SEQUENCE
   {
        contextId               ContextID,
        contextRequest          ContextRequest OPTIONAL,
        contextAttrAuditReq     ContextAttrAuditRequest OPTIONAL,
        commandRequests         SEQUENCE OF CommandRequest
   }

   ActionReply ::= SEQUENCE
   {
        contextId               ContextID,
        errorDescriptor         ErrorDescriptor OPTIONAL,
        contextReply            ContextRequest OPTIONAL,

        commandReply            SEQUENCE OF CommandReply
   }

   ContextRequest ::= SEQUENCE
   {
        priority                INTEGER(0..15) OPTIONAL,
        emergency               BOOLEAN OPTIONAL,
        topologyReq             SEQUENCE OF TopologyRequest OPTIONAL,
        ...
   }

   ContextAttrAuditRequest ::= SEQUENCE
   {
   topology     NULL OPTIONAL,
        emergency       NULL OPTIONAL,
        priority        NULL OPTIONAL,
        ...
   }

   CommandRequest ::= SEQUENCE
   {
        command                 Command,
        optional                NULL OPTIONAL,
        wildcardReturn          NULL OPTIONAL,
        ...
   }

   Command ::= CHOICE
   {
        addReq                  AmmRequest,
        moveReq                 AmmRequest,
        modReq                  AmmRequest,
        -- Add, Move, Modify requests have the same parameters
        subtractReq             SubtractRequest,
        auditCapRequest         AuditRequest,
        auditValueRequest       AuditRequest,
        notifyReq               NotifyRequest,
        serviceChangeReq        ServiceChangeRequest,
        ...
   }

   CommandReply ::= CHOICE
   {
        addReply                AmmsReply,
        moveReply               AmmsReply,
        modReply                AmmsReply,
        subtractReply           AmmsReply,
        -- Add, Move, Modify, Subtract replies have the same parameters

        auditCapReply           AuditReply,
        auditValueReply         AuditReply,
        notifyReply             NotifyReply,
        serviceChangeReply      ServiceChangeReply,
        ...
   }

   TopologyRequest ::= SEQUENCE
   {
        terminationFrom         TerminationID,
        terminationTo           TerminationID,
        topologyDirection       ENUMERATED
        {
                bothway(0),
                isolate(1),
                oneway(2)
        }
   }

   AmmRequest ::= SEQUENCE
   {
        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
   {

        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,
        ...
   }

   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,

        ...
   }

   -- For ServiceChangeResult, no parameters are mandatory.  Hence the
   -- 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,
        ...
   }

   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),
                ...
   }

   -- In PropertyParm, value is a SEQUENCE OF octet string.  When sent
   -- by an MGC the interpretation is as follows:
   -- empty sequence means CHOOSE
   -- one element sequence specifies value
   -- longer sequence means "choose one of the values"
   -- The relation field may only be selected if the value sequence
   -- has length 1.  It indicates that the MG has to choose a value
   -- for the property. E.g., x > 3 (using the greaterThan
   -- value for relation) instructs the MG to choose any value larger
   -- than 3 for property x.
   -- The range field may only be selected if the value sequence
   -- has length 2.  It indicates that the MG has to choose a value
   -- in the range between the first octet in the value sequence and
   -- the trailing octet in the value sequence, including the
   -- boundary values.
   -- When sent by the MG, only responses to an AuditCapability request
   -- 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

   }

   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),
         ...
   }

   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
   }

   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
   }

   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

   {
        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),

        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
        ...
   }

   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

   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

   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 )

   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

   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

   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 )

   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 ]

   ; 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

   ;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)

   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)

   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           ; "/"

   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")

   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")

   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

   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

   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

      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

   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)

   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

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

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

      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

      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

      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

      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

      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)

   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)

      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

      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

      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

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.

   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

   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

   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

       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

   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

   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.

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.

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.

   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

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)

   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

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

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

        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

   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

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.

                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.

                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)

        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.

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)

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

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

   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

        -------
        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.

   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.

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.

   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)

        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

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)

   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.

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

E.13.4 Statistics

None

E.13.5 Procedures

None

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.

   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 $

   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}}

      }
   }

   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 {

            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
                     }
                }
             }
          }
       }
   }

   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
                    },

                    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 {

         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 {

      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
   }}

}
}

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 {

             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,

                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

   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

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.

Status of this Memo

Copyright Notice

Abstract

1. SCOPE

2. REFERENCES

2.1 Normative references

2.2 Informative references

3. DEFINITIONS

4. ABBREVIATIONS

5. CONVENTIONS

6. CONNECTION MODEL

6.1 Contexts

6.1.1 Context Attributes and Descriptors

6.1.2 Creating, Deleting and Modifying Contexts

6.2 Terminations

6.2.1 Termination Dynamics

6.2.2 TerminationIDs

6.2.3 Packages

6.2.4 Termination Properties and Descriptors

6.2.5 Root Termination

7. COMMANDS

7.1 Descriptors

7.1.1 Specifying Parameters

7.1.2 Modem Descriptor

7.1.3 Multiplex Descriptor

7.1.4 Media Descriptor

7.1.5 Termination State Descriptor

7.1.6 Stream Descriptor

7.1.7 LocalControl Descriptor

7.1.8 Local and Remote Descriptors

7.1.9 Events Descriptor

7.1.10 EventBuffer Descriptor

7.1.11 Signals Descriptor

7.1.12 Audit Descriptor

7.1.13 ServiceChange Descriptor

7.1.14 DigitMap Descriptor

7.1.15 Statistics Descriptor

7.1.16 Packages Descriptor

7.1.17 ObservedEvents Descriptor

7.1.18 Topology Descriptor

7.2 Command Application Programming Interface

7.2.1 Add

7.2.2 Modify

7.2.3 Subtract

7.2.4 Move

7.2.5 AuditValue

7.2.6 AuditCapabilities

7.2.7 Notify

7.2.8 ServiceChange

912 Mux Capability Failure 913 Signal Capability Failure 914 Event Capability Failure 915 State Loss

7.2.9 Manipulating and Auditing Context Attributes

7.2.10 Generic Command Syntax

7.3 Command Error Codes

8. TRANSACTIONS

8.1 Common Parameters

8.1.1 Transaction Identifiers

8.1.2 Context Identifiers

8.2 Transaction Application Programming Interface

8.2.1 TransactionRequest

8.2.2 TransactionReply

8.2.3 TransactionPending

8.3 Messages

9. TRANSPORT

9.1 Ordering of Commands

9.2 Protection against Restart Avalanche

10. SECURITY CONSIDERATIONS

10.1 Protection of Protocol Connections

10.2 Interim AH scheme

10.3 Protection of Media Connections

11. MG-MGC CONTROL INTERFACE

11.1 Multiple Virtual MGs

11.2 Cold Start

11.3 Negotiation of Protocol Version

11.4 Failure of an MG

11.5 Failure of an MGC

12. PACKAGE DEFINITION

12.1 Guidelines for defining packages

12.1.1 Package

12.1.2 Properties

12.1.3 Events

912 Mux Capability Failure
913 Signal Capability Failure
914 Event Capability Failure
915 State Loss

12.2 Guidelines to defining Properties, Statistics and Parameters to
Events and Signals.

H.221 2001 Octet Ref.: rec. H.245,
string H222LogicalChannelParameters

0 - unspecified
1 - 8kbit/s
2 - 16kbit/s
3 - 32kbit/s

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)