Network Working Group C. Groves
Request for Comments: 3525 M. Pantaleo
Obsoletes: 3015 LM EriCsson
Category: Standards Track T. Anderson
Consultant
T. Taylor
Nortel Networks
Editors
June 2003

Gateway Control Protocol Version 1

Status of this Memo

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

Copyright Notice

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

Abstract

This document defines the protocol used between elements of a
physically decomposed multimedia gateway, i.e., a Media Gateway and a
Media Gateway Controller. The protocol presented in this document
meets the requirements for a media gateway control protocol as
presented in RFC2805.

This document replaces RFC3015. It is the result of continued
cooperation between the IETF Megaco Working Group and ITU-T Study
Group 16. It incorporates the original text of RFC3015, modified by
corrections and clarifications discussed on the Megaco
E-mail list and incorporated into the Study Group 16 Implementor's
Guide for Recommendation H.248. The present version of this document
underwent ITU-T Last Call as Recommendation H.248 Amendment 1.
Because of ITU-T renumbering, it was published by the ITU-T as
Recommendation H.248.1 (03/2002), Gateway Control Protocol Version 1.

Users of this specification are advised to consult the H.248 Sub-
series Implementors' Guide at http://www.itu.int/itudoc/itu-
t/com16/implgd for additional corrections and clarifications.

Conventions used in this document

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

Table of Contents

1 Scope.........................................................5
1.1 Changes From RFC3015.....................................5
1.2 Differences From ITU-T Recommendation H.248.1 (03/2002)...5
2 References....................................................6
2.1 Normative references......................................6
2.2 Informative references....................................9
3 Definitions..................................................10
4 Abbreviations................................................11
5 Conventions..................................................12
6 Connection model.............................................13
6.1 Contexts.................................................16
6.2 Terminations.............................................17
6.2.1 Termination dynamics.................................21
6.2.2 TerminationIDs.......................................21
6.2.3 Packages.............................................22
6.2.4 Termination properties and descriptors...............23
6.2.5 Root Termination.....................................25
7 Commands.....................................................26
7.1 Descriptors..............................................27
7.1.1 Specifying parameters................................27
7.1.2 Modem descriptor.....................................28
7.1.3 Multiplex descriptor.................................28
7.1.4 Media descriptor.....................................29
7.1.5 TerminationState descriptor..........................29
7.1.6 Stream descriptor....................................30
7.1.7 LocalControl descriptor..............................31
7.1.8 Local and Remote descriptors.........................32
7.1.9 Events descriptor....................................35
7.1.10 EventBuffer descriptor..............................38
7.1.11 Signals descriptor..................................38
7.1.12 Audit descriptor....................................40
7.1.13 ServiceChange descriptor............................41
7.1.14 DigitMap descriptor.................................41
7.1.15 Statistics descriptor...............................46
7.1.16 Packages descriptor.................................47
7.1.17 ObservedEvents descriptor...........................47
7.1.18 Topology descriptor.................................47
7.1.19 Error Descriptor....................................50
7.2 Command Application Programming Interface................50
7.2.1 Add..................................................51

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

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

E.13 TDM Circuit Package....................................182
APPENDIX I EXAMPLE CALL FLOWS (INFORMATIVE)...................184
A.1 Residential Gateway to Residential Gateway Call.........184
A.1.1 Programming Residential GW Analog Line Terminations
for Idle Behavior...................................184
A.1.2 Collecting Originator Digits and Initiating
Termination.........................................186
APPENDIX II Changes From RFC3015............................195
Intellectual Property Rights..................................210
Acknowledgments...............................................211
Authors' Addresses............................................212
Full Copyright Statement......................................213

1 Scope

The present document, which is identical to the published version of
ITU-T Recommendation H.248.1 (03/2002) except as noted below, defines
the protocols used between elements of a physically decomposed
multimedia gateway. There are no functional differences from a
system view between a decomposed gateway, with distributed sub-
components potentially on more than one physical device, and a
monolithic gateway sUCh as described in ITU-T Recommendation H.246.
This document does not define how gateways, multipoint control units
or interactive voice response units (IVRs) work. Instead it creates
a general framework that is suitable for these applications.

Packet network interfaces may include IP, ATM or possibly others.
The interfaces will support a variety of Switched Circuit Network
(SCN) signalling systems, including tone signalling, ISDN, ISUP, QSIG
and GSM. National variants of these signalling systems will be
supported where applicable.

1.1 Changes From RFC3015

The differences between this document and RFC3015 are documented in
Appendix II.

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

This document differs from the corresponding ITU-T publication in the
following respects:

- Added IETF front matter in place of the corresponding ITU-T
material.

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

- The IETF conventions have been stated as governing this document.
As discussed in section 5 below, this gives slightly greater
strength to "should" requirements.

- The Scope section (just above) has been edited slightly to suit
its IETF context.

- Added normative references to RFCs 2026 and 2119.

- Figures 4, 5, and 6 show the centre of the context for greater
clarity. Also added Figure 6a showing an important additional
example.

- Added a paragraph in section 7.1.18 which was approved in the
Implementor's Guide but lost inadvertently in the ITU-T approved
version.

- This document incorporates corrections to the informative examples
in Appendix I which also appear in H.248.1 version 2, but which
were not picked up in H.248.1 (03/2002).

- This document includes a new Appendix II listing all the changes
from RFC3015.

- This document includes an Acknowledgements section listing the
authors of RFC3015 but also many other people who contributed to
the development of the Megaco/H.248.x protocol.

- Moved the Intellectual Property declaration to its usual place in
an IETF document and added a reference to declarations on the IETF
web site.

2 References

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

2.1 Normative references

- ITU-T Recommendation H.225.0 (1999), Call signalling protocols and
media stream packetization for packet-based multimedia
communication systems.

- ITU-T Recommendation H.235 (1998), 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.246 (1998), Interworking of H-series
multimedia terminals with H-series multimedia terminals and
voice/voiceband terminals on GSTN and ISDN.

- ITU-T Recommendation H.248.8 (2002), H.248 Error Codes and Service
Change Reasons.

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

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

- ITU-T Recommendation I.363.2 (1997), B-ISDN ATM adaptation layer
(AAL) specification: Type 2 AAL.

- ITU-T Recommendation I.363.5 (1996), B-ISDN ATM adaptation layer
(AAL) specification: Type 5 AAL.

- ITU-T Recommendation I.366.1 (1998), Segmentation and Reassembly
Service Specific Convergence Sublayer for the AAL type 2.

- ITU-T Recommendation I.366.2 (1999), AAL type 2 service specific
convergence sublayer for trunking.

- ITU-T Recommendation I.371 (2000), Traffic control and congestion
control in B-ISDN.

- ITU-T Recommendation Q.763 (1999), Signalling System No. 7 - ISDN
user part formats and codes.

- ITU-T Recommendation Q.765.5 (2001), Application transport
mechanism - Bearer independent call control (BICC).

- ITU-T Recommendation Q.931 (1998), 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 (1995), Digital Subscriber Signalling
System No. 2 (DSS2) - User-Network Interface (UNI) - Layer 3
specification for basic call/connection control.

- ITU-T Recommendation Q.2941.1 (1997), Digital Subscriber
Signalling System No. 2 - Generic identifier transport.

- ITU-T Recommendation Q.2961.1 (1995), Additional signalling
capabilities to support traffic parameters for the tagging option
and the sustainable call rate parameter set.

- ITU-T Recommendation Q.2961.2 (1997), Additional traffic
parameters: Support of ATM transfer capability in the broadband
bearer capability information element.

- ITU-T Recommendation Q.2965.1 (1999), Digital subscriber
signalling system No. 2 - Support of Quality of Service classes.

- ITU-T Recommendation Q.2965.2 (1999), Digital subscriber
signalling system No. 2 - Signalling of individual Quality of
Service parameters.

- ITU-T Recommendation V.76 (1996), Generic multiplexer using V.42
LAPM-based procedures.

- ITU-T Recommendation X.213 (1995), Information technology - Open
Systems Interconnection - Network service definition plus
Amendment 1 (1997), Addition of the Internet protocol address
format identifier.

- ITU-T Recommendation X.680 (1997), Information technology -
Abstract Syntax Notation One (ASN.1): Specification of basic
notation.

- ITU-T Recommendation X.690 (1997), Information Technology - ASN.1
Encoding Rules: Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished Encoding Rules
(DER).

- ATM Forum (1996), ATM User-Network Interface (UNI) Signalling
Specification - Version 4.0.

[RFC1006] Rose, M. and D. Cass, "ISO Transport Service on top of the
TCP, Version 3", STD 35, RFC1006, May 1987.

[RFC2026] Brander, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC2026, October 1996.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.

[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC2234, November 1997.

[RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC2327, April 1998.

[RFC2402] Kent, S. and R. Atkinson, "IP Authentication Header", RFC
2402, November 1998.

[RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating Security
Payload (ESP)", RFC2406, 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 (1999), 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 H.226 (1998), Channel aggregation protocol
for multilink operation on circuit-switched networks

- ITU-T Recommendation Q.724 (1998), Signalling procedures.

- ITU-T Recommendation Q.764 (1999), Signalling system No. 7 - ISDN
user part signalling procedures.

- ITU-T Recommendation Q.1902.4 (2001), Bearer independent call
control protocol - Basic call procedures.

[RFC768] Postel, J., "User Datagram Protocol", STD 6, RFC768,
August 1980.

[RFC791] Postel, J., "Internet Protocol", STD 5, RFC791, September
1981.

[RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.

[RFC1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD
51, RFC1661, July 1994.

[RFC1889] Schulzrinne, H., Casner, S., Frederick, R. and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", RFC1889, January 1996.

[RFC1890] Schulzrinne, H. and G. Fokus, "RTP Profile for Audio and
Video Conferences with Minimal Control", RFC1890,
January 1996.

[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC2401, November 1998.

[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC2460, December 1998.

[RFC2543] Handley, M., Schulzrinne, H., Schooler, E. and J.
Rosenberg, "SIP: Session Initiation Protocol", RFC2543,
March 1999.

[RFC2805] Greene, N., Ramalho, M. and B. Rosen, "Media Gateway
Control Protocol Architecture and Requirements", RFC2805,
April 2000.

3 Definitions

This document defines the following terms:

Access gateway:
A type of gateway that provides a User-Network Interface (UNI) such
as ISDN.

Descriptor:
A syntactic element of the protocol that groups related properties.
For instance, the properties of a media flow on the MG can be set by
the MGC by including the appropriate descriptor in a command.

Media Gateway (MG):
The media gateway converts media provided in one type of network to
the format required in another type of network. For example, a MG
could terminate bearer channels from a switched circuit network
(e.g., DS0s) and media streams from a packet network (e.g., RTP
streams in an IP network). This gateway may be capable of processing
audio, video and T.120 alone or in any combination, and will be
capable of full duplex media translations. The MG may also play
audio/video messages and perform other IVR functions, or may perform
media conferencing.

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 RFCdocument uses the following abbreviations:

ALF Application Layer Framing

ATM Asynchronous Transfer Mode

CAS Channel Associated Signalling

DTMF Dual Tone Multi-Frequency

FAS Facility Associated Signalling

GSM Global System for Mobile communications

GW GateWay

IANA Internet Assigned Numbers Authority (superseded by Internet
Corporation for Assigned Names and Numbers - ICANN)

IP Internet Protocol

ISUP ISDN User Part

IVR Interactive Voice Response

MG Media Gateway

MGC Media Gateway Controller

NFAS Non-Facility Associated Signalling

PRI Primary Rate Interface

PSTN Public Switched Telephone Network

QoS Quality of Service

RTP Real-time Transport Protocol

SCN Switched Circuit Network

SG Signalling Gateway

SS7 Signalling System No. 7

5 Conventions

In the H.248.1 Recommendation, "SHALL" refers to a mandatory
requirement, while "SHOULD" refers to a suggested but optional
feature or procedure. The term "MAY" refers to an optional course of
action without eXPressing a preference. Note that these definition
are overridden in the present document by the RFC2119 conventions
stated at the beginning of this document. RFC2119 has a more
precise definition of "should" than is provided by the ITU-T.

6 Connection model

The connection model for the protocol describes the logical entities,
or objects, within the Media Gateway that can be controlled by the
Media Gateway Controller. The main abstractions used in the
connection model are Terminations and Contexts.

A Termination sources and/or sinks one or more streams. In a
multimedia conference, a Termination can be multimedia and sources or
sinks multiple media streams. The media stream parameters, as well
as modem, and bearer parameters are encapsulated within the
Termination.

A Context is an association between a collection of Terminations.
There is a special type of Context, the null Context, which contains
all Terminations that are not associated to any other Termination.
For instance, in a decomposed access gateway, all idle lines are
represented by Terminations in the null Context.

Following is a graphical depiction of these concepts. The diagram of
Figure 1 gives several examples and is not meant to be an
all-inclusive illustration. The asterisk box in each of the Contexts
represents the logical association of Terminations implied by the
Context.

+------------------------------------------------------+
Media Gateway
+-------------------------------------------------+
Context +-------------+
Termination
-------------
+-------------+ +-> SCN Bearer <---+->
Termination +-----+ Channel
------------- ---+ +-------------+
<-+---> RTP Stream --- *
---+ +-------------+
+-------------+ +-----+ Termination
-------------
+-> SCN Bearer <---+->
Channel
+-------------+
+-------------------------------------------------+


+------------------------------+
(NULL Context) Context
+-------------+ +-------------+
Termination +-----+ Termination
------------- -------------
SCN Bearer * ------ SCN Bearer <---+->
Channel Channel
+-------------+ +-----+ +-------------+
+------------------------------+


+-------------------------------------------------+
Context
+-------------+ +-------------+
Termination +-----+ Termination
------------- -------------
<-+---> SCN Bearer --- * ------ SCN Bearer <---+->
Channel Channel
+-------------+ +-----+ +-------------+
+-------------------------------------------------+
___________________________________________________
+------------------------------------------------------+

Figure 1: Examples of Megaco/H.248 Connection Model

The example in Figure 2 shows an example of one way to accomplish a
call-waiting scenario in a decomposed access gateway, illustrating
the relocation of a Termination between Contexts. Terminations T1
and T2 belong to Context C1 in a two-way audio call. A second audio
call is waiting for T1 from Termination T3. T3 is alone in Context
C2. T1 accepts the call from T3, placing T2 on hold. This action
results in T1 moving into Context C2, as shown in Figure 3.

+------------------------------------------------------+
Media Gateway
+-------------------------------------------------+
Context C1
+-------------+ +-------------+
Term. T2 +-----+ Term. T1
------------- -------------
<-+---> RTP Stream --- * ------ SCN Bearer <---+->
Channel
+-------------+ +-----+ +-------------+
+-------------------------------------------------+

+-------------------------------------------------+
Context C2
+-------------+
+-----+ Term. T3
-------------
* ------ SCN Bearer <---+->
Channel
+-----+ +-------------+
+-------------------------------------------------+
+------------------------------------------------------+

Figure 2: Example Call Waiting Scenario / Alerting Applied to T1

+------------------------------------------------------+
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. Priority 0 is the lowest priority and a priority
of 15 is the highest priority.

- 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 (see 7.1.11).
Terminations may be programmed to detect Events, the occurrence of
which can trigger notification messages to the MGC, or action by the
MG. Statistics may be accumulated on a Termination. Statistics are
reported to the MGC upon request (by means of the AuditValue command,
see 7.2.5) and when the Termination is taken out of the call it is
in.

Multimedia gateways may process multiplexed media streams. For
example, Recommendation H.221 describes a frame structure for
multiple media streams multiplexed on a number of digital 64 kbit/s
channels. Such a case is handled in the connection model in the
following way. For every bearer channel that carries part of the
multiplexed streams, there is a physical or ephemeral "bearer
Termination". The bearer Terminations that source/sink the digital
channels are connected to a separate Termination called the
"multiplexing Termination". The multiplexing termination is an
ephemeral termination representing a frame-oriented session. The
MultiplexDescriptor for this Termination describes the multiplex used
(e.g., H.221 for an H.320 session) and indicates the order in which
the contained digital channels are assembled into a frame.

Multiplexing terminations may be cascades (e.g., H.226 multiplex of
digital channels feeding into a H.223 multiplex supporting an H.324
session).

The individual media streams carried in the session are described by
StreamDescriptors on the multiplexing Termination. These media
streams can be associated with streams sourced/sunk by Terminations
in the Context other than the bearer Terminations supporting the
multiplexing Termination. Each bearer Termination supports only a
single data stream. These data streams do not appear explicitly as
streams on the multiplexing Termination and they are hidden from the
rest of the context.

Figures 4, 5, 6, and 6a illustrate typical applications of the
multiplexing termination and Multiplex Descriptor.

+-----------------------------------+
Context +-------+
+----+
Circuit 1 --- TC1---------+ Tmux
+----+ (Str 1) Audio +-----+
+-----*-----+ -----
+----+ H.22x Stream 1
Circuit 2 --- TC2---------+ multi- TR1
+----+ (Str 1) plex (RTP)
Video
+----+ +-----*-----+ -----
Circuit 3 --- TC3---------+ Stream 2
/ +----+ (Str 1) +-----+
/ +-------+
/ +----------------------------------+
Audio, video, and control
signals are carried in frames Tmux is an ephemeral with two
spanning the circuits. explicit Stream Descriptors
and a Multiplex Descriptor.

Figure 4: Multiplexed Termination Scenario - Circuit to Packet
(Asterisks * denote the centre of the context)

Context
+--------------------------------------+
+-------+ +-------+
+----+ +----+
Circuit 1 ---- TC1---+ Tmux1 Audio Tmux2 +--- TC4---
+----+ +---*----+ +----+
Str 1
+----+ H.22x H.22x +----+
Circuit 2 ---- TC2---+ multi- multi-+--- TC5---
+----+ plex plex +----+
Video
+----+ +---*----+ +----+
Circuit 3 ---- TC3---+ Str 2 +--- TC6---
+----+ +----+
+-------+ +-------+
+----------------------/--------------+
/
Tmux1 and Tmux2 are ephemerals each with two
explicit Stream Descriptors and a Multiplex Descriptor.

Figure 5: Multiplexed Termination Scenario - Circuit to Circuit
(Asterisks * denote the centre of the context)

+-----------------------------------+
Context +-------+
+----+
Circuit 1 --- TC1---------+ Tmux
+----+ (Str 1) Audio +-----+
+-----*-----+ TR1 -----
+----+ H.22x Stream 1 (RTP)
Circuit 2 --- TC2---------+ multi- +-----+
+----+ (Str 1) plex
Video +-----+
+----+ +-----*-----+ TR2 -----
Circuit 3 --- TC3---------+ Stream 2 (RTP)
/ +----+ (Str 1) +-----+
/ +-------+
/ +----------------------------------+
Audio, video, and control Tmux is an ephemeral with two
signals are carried in frames explicit Stream Descriptors and
spanning the circuits. and a Multiplex Descriptor.

Figure 6: Multiplexed Termination Scenario - Single to Multiple
Terminations
(Asterisks * denote the centre of the context)

Context
+---------------------------------------------+
+-------+ +-------+
Cct 1 +----+ Audio +-----+
---- TC1---+ Tmux1 Tmux2 +-----*----- TR1 -----
+----+ Stream 1 (RTP)
Data +-----+
Cct 2 +----+ H.226 +-------+ H.223
---- TC2---+ multi-(Str 1) multi- Control +-----+
+----+ plex plex +-----*-----+ Tctl-----
Stream 3 +-----+
Cct 3 +----+
---- TC3---+ +-----+
+----+ +-----*-----+ TR2 -----
+-------+ Video (RTP)
+-------+ Stream 2 +-----+

+---------------------------------------------+
Tmux1 has a Multiplex Descriptor and a single data stream.
Tmux2 has a Multiplex Descriptor with a single bearer and
three explicit Stream Descriptors.

Figure 6a: Multiplexed Termination Scenario - Cascaded Multiplexes
(Asterisks * denote the centre of the context)
Note: this figure does not appear in Rec. H.248.1

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

6.2.1 Termination dynamics

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

6.2.2 TerminationIDs

Terminations are referenced by a TerminationID, which is an arbitrary
schema chosen by the MG.

TerminationIDs of physical Terminations are provisioned in the Media
Gateway. The TerminationIDs may be chosen to have structure. For
instance, a TerminationID may consist of trunk group and a trunk
within the group.

A wildcarding mechanism using two types of wildcards can be used with
TerminationIDs. The two wildcards are ALL and CHOOSE. The former is
used to address multiple Terminations at once, while the latter is
used to indicate to a media gateway that it must select a Termination
satisfying the partially specified TerminationID. This allows, for
instance, that a MGC instructs a MG to choose a circuit within a
trunk group.

When ALL is used in the TerminationID of a command, the effect is
identical to repeating the command with each of the matching
TerminationIDs. The use of ALL does not address the ROOT
termination. Since each of these commands may generate a response,
the size of the entire response may be large. If individual
responses are not required, a wildcard response may be requested. In
such a case, a single response is generated, which contains the UNION
of all of the individual responses which otherwise would have been
generated, with duplicate values suppressed. For instance, given a
Termination Ta with properties p1=a, p2=b and Termination Tb with

properties p2=c, p3=d, a UNION response would consist of a wildcarded
TerminationId and the sequence of properties p1=a, p2=b,c and p3=d.
Wildcard response may be particularly useful in the Audit commands.

The encoding of the wildcarding mechanism is detailed in Annexes A
and B.

6.2.3 Packages

Different types of gateways may implement Terminations that have
widely differing characteristics. Variations in Terminations are
accommodated in the protocol by allowing Terminations to have
optional Properties, Events, Signals and Statistics implemented by
MGs.

In order to achieve MG/MGC interoperability, such options are grouped
into Packages, and typically a Termination realizes a set of such
Packages. More information on definition of packages can be found in
clause 12. An MGC can audit a Termination to determine which
Packages it realizes.

Properties, Events, Signals and Statistics defined in Packages, as
well as parameters to them, are referenced by identifiers (Ids).
Identifiers are scoped. For each package, PropertyIds, EventIds,
SignalIds, StatisticsIds and ParameterIds have unique name spaces and
the same identifier may be used in each of them. Two PropertyIds in
different packages may also have the same identifier, etc.

To support a particular package the MG must support all properties,
signals, events and statistics defined in a package. It must also
support all Signal and Event parameters. The MG may support a subset
of the values listed in a package for a particular Property or
Parameter.

When packages are extended, the properties, events, signals and
statistics defined in the base package can be referred to using
either the extended package name or the base package name. For
example, if Package A defines event e1, and Package B extends Package
A, then B/e1 is an event for a termination implementing Package B. By
definition, the MG MUST also implement the base Package, but it is
optional to publish the base package as an allowed interface. If it
does publish A, then A would be reported on the Package Descriptor
in AuditValue as well as B, and event A/e1 would be available on a
termination. If the MG does not publish A, then only B/e1 would be
available. If published through AuditValue, A/e1 and B/e1 are the
same event.

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

6.2.4 Termination properties and descriptors

Terminations have properties. The properties have unique
PropertyIDs. Most properties have default values, which are
explicitly defined in this protocol specification or in a package
(see clause 12) or set by provisioning. If not provisioned
otherwise, the properties in all descriptors except TerminationState
and LocalControl default to empty/"no value" when a Termination is
first created or returned to the null Context. The default contents
of the two exceptions are described in 7.1.5 and 7.1.7.

The provisioning of a property value in the MG will override any
default value, be it supplied in this protocol specification or in a
package. Therefore if it is essential for the MGC to have full
control over the property values of a Termination, it should supply
explicit values when ADDing the Termination to a Context.
Alternatively, for a physical Termination the MGC can determine any
provisioned property values by auditing the Termination while it is
in the NULL Context.

There are a number of common properties for Terminations and
properties specific to media streams. The common properties are also
called the Termination state properties. For each media stream,
there are local properties and properties of the received and
transmitted flows.

Properties not included in the base protocol are defined in Packages.
These properties are referred to by a name consisting of the
PackageName and a PropertyId. Most properties have default values
described in the Package description. Properties may be read-only or
read/write. The possible values of a property may be audited, as can
their current values. For properties that are read/write, the MGC
can set their values. A property may be declared as "Global" which
has a single value shared by all Terminations realizing the package.
Related properties are grouped into descriptors for convenience.

When a Termination is added to a Context, the value of its read/write
properties can be set by including the appropriate descriptors as
parameters to the Add command. Similarly, a property of a
Termination in a Context may have its value changed by the Modify
command.

Properties may also have their values changed when a Termination is
moved from one Context to another as a result of a Move command. In
some cases, descriptors are returned as output from a command.

In general, if a Descriptor is completely omitted from one of the
aforementioned Commands, the properties in that Descriptor retain
their prior values for the Termination(s) upon which the Command
acts. On the other hand, if some read/write properties are omitted
from a Descriptor in a Command (i.e., the Descriptor is only
partially specified), those properties will be reset to their default
values for the Termination(s) upon which the Command acts, unless the
package specifies other behavior. For more details, see clause 7.1
dealing with the individual Descriptors.

The following table lists all of the possible descriptors and their
use. Not all descriptors are legal as input or output parameters to
every command.

Descriptor name Description

Modem Identifies modem type and properties when
applicable

Mux Describes multiplex type for multimedia
Terminations (e.g., H.221, H.223, H.225.0) and
Terminations forming the input mux

Media A list of media stream specifications (see 7.1.4)

TerminationState Properties of a Termination (which can be defined
in Packages) that are not stream specific

Stream A list of remote/local/localControl descriptors for
a single stream

Local Contains properties that specify the media flows
that the MG receives from the remote entity.

Remote Contains properties that specify the media flows
that the MG sends to the remote entity.

LocalControl Contains properties (which can be defined in
packages) that are of interest between the MG and
the MGC.

Events Describes events to be detected by the MG and what
to do when an event is detected.

EventBuffer Describes events to be detected by the MG when
Event Buffering is active.

Signals Describes signals (see 7.1.11) applied to
Terminations.

Audit In Audit commands, identifies which information is
desired.

Packages In AuditValue, returns a list of Packages realized
by Termination.

DigitMap Defines patterns against which sequences of a
specified set of events are to be matched so they
can be reported as a group rather than singly.

ServiceChange In ServiceChange, what, why service change
occurred, etc.

ObservedEvents In Notify or AuditValue, report of events observed.

Statistics In Subtract and Audit, report of Statistics kept on
a Termination.

Topology Specifies flow directions between Terminations in a
Context.

Error Contains an error code and optionally error text;
it may occur in command replies and in Notify
requests.

6.2.5 Root Termination

Occasionally, a command must refer to the entire gateway, rather than
a Termination within it. A special TerminationID, "Root" is reserved
for this purpose. Packages may be defined on Root. Root thus may
have properties, events and statistics (signals are not appropriate
for root). Accordingly, the root TerminationID may appear in:

- 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 and
statistics 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. Error code
410 - Incorrect identifier shall be returned in these cases.

7 Commands

The protocol provides commands for manipulating the logical entities
of the protocol connection model, Contexts and Terminations.
Commands provide control at the finest level of granularity supported
by the protocol. For example, Commands exist to add Terminations to
a Context, modify Terminations, subtract Terminations from a Context,
and audit properties of Contexts or Terminations. Commands provide
for complete control of the properties of Contexts and Terminations.
This includes specifying which events a Termination is to report,
which signals/actions are to be applied to a Termination and
specifying the topology of a Context (who hears/sees whom).

Most commands are for the specific use of the Media Gateway
Controller as command initiator in controlling Media Gateways as
command responders. The exceptions are the Notify and ServiceChange
commands: Notify is sent from Media Gateway to Media Gateway
Controller, and ServiceChange may be sent by either entity. Below is
an overview of the commands; they are explained in more detail in
7.2.

1) Add - The Add command adds a Termination to a Context. The Add
command on the first Termination in a Context is used to create a
Context.

2) Modify - The Modify command modifies the properties, events and
signals of a Termination.

3) Subtract - The Subtract command disconnects a Termination from its
Context and returns statistics on the Termination's participation
in the Context. The Subtract command on the last Termination in a
Context deletes the Context.

4) Move - The Move command atomically moves a Termination to another
Context.

5) AuditValue - The AuditValue command returns the current state of
properties, events, signals and statistics of Terminations.

6) AuditCapabilities - The AuditCapabilities command returns all the
possible values for Termination properties, events and signals
allowed by the Media Gateway.

7) Notify - The Notify command allows the Media Gateway to inform the
Media Gateway Controller of the occurrence of events in the Media
Gateway.

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

These commands are detailed in 7.2.1 through 7.2.8.

7.1 Descriptors

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

7.1.1 Specifying parameters

Command parameters are structured into a number of descriptors. In
general, the text format of descriptors is
DescriptorName=<someID>{parm=value, parm=value, ...}.

Parameters may be fully specified, overspecified or underspecified:

1) Fully specified parameters have a single, unambiguous value that
the command initiator is instructing the command responder to use
for the specified parameter.

2) Underspecified parameters, using the CHOOSE value, allow the
command responder to choose any value it can support.

3) Overspecified parameters have a list of potential values. The
list order specifies the command initiator's order of preference
of selection. The command responder chooses one value from
the offered list and returns that value to the command initiator.

If a required descriptor other than the Audit descriptor is
unspecified (i.e., entirely absent) from a command, the previous
values set in that descriptor for that Termination, if any, are
retained. In commands other than Subtract, a missing Audit
descriptor is equivalent to an empty Audit descriptor. The Behaviour
of the MG with respect to unspecified parameters within a descriptor
varies with the descriptor concerned, as indicated in succeeding
subclauses. Whenever a parameter is underspecified or overspecified,
the descriptor containing the value chosen by the responder is
included as output from the command.

Each command specifies the TerminationId the command operates on.
This TerminationId may be "wildcarded". When the TerminationId of a
command is wildcarded, the effect shall be as if the command was
repeated with each of the TerminationIds matched.

7.1.2 Modem descriptor

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

7.1.3 Multiplex descriptor

In multimedia calls, a number of media streams are carried on a
(possibly different) number of bearers. The multiplex descriptor
associates the media and the bearers. The descriptor includes the
multiplex type:

- H.221;

- H.223;

- H.226;

- V.76;

- possible extensions,

and a set of TerminationIDs representing the multiplexed bearers, in
order. For example:

Mux = H.221{ MyT3/1/2, MyT3/2/13, MyT3/3/6, MyT3/21/22}

7.1.4 Media descriptor

The Media descriptor specifies the parameters for all the media
streams. These parameters are structured into two descriptors: a
TerminationState descriptor, which specifies the properties of a
Termination that are not stream dependent, and one or more Stream
descriptors each of which describes a single media stream.

A stream is identified by a StreamID. The StreamID is used to link
the streams in a Context that belong together. Multiple streams
exiting a Termination shall be synchronized with each other. Within
the Stream descriptor, there are up to three subsidiary descriptors:
LocalControl, Local, and Remote. The relationship between these
descriptors is thus:

Media descriptor
TerminationState Descriptor
Stream descriptor
LocalControl descriptor
Local descriptor
Remote descriptor

As a convenience, LocalControl, Local, or Remote descriptors may be
included in the Media descriptor without an enclosing Stream
descriptor. In this case, the StreamID is assumed to be 1.

7.1.5 TerminationState descriptor

The TerminationState descriptor contains the ServiceStates property,
the EventBufferControl property and properties of a Termination
(defined in Packages) that are not stream specific.

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

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 7.1.9 for details.

7.1.6 Stream descriptor

A Stream descriptor specifies the parameters of a single
bidirectional stream. These parameters are structured into three
descriptors: one that contains Termination properties specific to a
stream and one each for local and remote flows. The Stream
Descriptor includes a StreamID which identifies the stream. Streams
are created by specifying a new StreamID on one of the Terminations
in a Context. A stream is deleted by setting empty Local and Remote
descriptors for the stream with ReserveGroup and ReserveValue in
LocalControl set to "false" on all Terminations in the Context that
previously supported that stream.

StreamIDs are of local significance between MGC and MG and they are
assigned by the MGC. Within a Context, StreamID is a means by which
to indicate which media flows are interconnected: streams with the
same StreamID are connected.

If a Termination is moved from one Context to another, the effect on
the Context to which the Termination is moved is the same as in the
case that a new Termination were added with the same StreamIDs as the
moved Termination.

7.1.7 LocalControl descriptor

The LocalControl descriptor contains the Mode property, the
ReserveGroup and ReserveValue properties and properties of a
Termination (defined in Packages) that are stream specific, and are
of interest between the MG and the MGC. Values of properties may be
underspecified as in 7.1.1.

The allowed values for the mode property are send-only, receive-only,
send/receive, inactive and loop-back. "Send" and "receive" are with
respect to the exterior of the Context, so that, for example, a
stream set to mode=sendOnly does not pass received media into the
Context. The default value for the mode property is "Inactive".
Signals and Events are not affected by mode.

The boolean-valued Reserve properties, ReserveValue and ReserveGroup,
of a Termination indicate what the MG is expected to do when it
receives a Local and/or Remote descriptor.

If the value of a Reserve property is True, the MG SHALL reserve
resources for all alternatives specified in the Local and/or Remote
descriptors for which it currently has resources available. It SHALL
respond with the alternatives for which it reserves resources. If it
cannot not support any of the alternatives, it SHALL respond with a
reply to the MGC that contains empty Local and/or Remote descriptors.
If media begins to flow while more than a single alternative is
reserved, media packets may be sent/received on any of the
alternatives and must be processed, although only a single
alternative may be active at any given time.

If the value of a Reserve property is False, the MG SHALL choose one
of the alternatives specified in the Local descriptor (if present)
and one of the alternatives specified in the Remote descriptor (if
present). If the MG has not yet reserved resources to support the
selected alternative, it SHALL reserve the resources. If, on the
other hand, it already reserved resources for the Termination
addressed (because of a prior exchange with ReserveValue and/or
ReserveGroup equal to True), it SHALL release any excess resources it
reserved previously. Finally, the MG shall send a reply to the MGC
containing the alternatives for the Local and/or Remote descriptor
that it selected. If the MG does not have sufficient resources to
support any of the alternatives specified, it SHALL respond with
error 510 (insufficient resources).

The default value of ReserveValue and ReserveGroup is False. More
information on the use of the two Reserve properties is provided in
7.1.8.

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 RFC2327 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.

A Stream Descriptor specifies a single bi-directional media stream
and so a single session description MUST NOT include more than one
media description ("m=" line). A Stream Descriptor may contain
additional session descriptions as alternatives. Each media stream
for a termination must appear in distinct Stream Descriptors. When
multiple session descriptions are provided in one descriptor, the
"v=" lines are required as delimiters; otherwise they are optional in
session descriptions sent to the MG. Implementations shall accept
session descriptions that are fully conformant to 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:

1) unspecified (i.e., absent);

2) empty;

3) underspecified through use of CHOOSE in a property value;

4) fully specified; or

5) overspecified through presentation of multiple groups of
properties and possibly multiple property values in one or more of
these groups.

Where the descriptors have been passed from the MGC to the MG, they
are interpreted according to the rules given in 7.1.1, with the
following additional comments for clarification:

a) An unspecified Local or Remote descriptor is considered to be a
missing mandatory parameter. It requires the MG to use whatever
was last specified for that descriptor. It is possible that there
was no previously specified value, in which case the descriptor
concerned is ignored in further processing of the command.

b) An empty Local (Remote) descriptor in a message from the MGC
signifies a request to release any resources reserved for the
media flow received (sent).

c) If multiple groups of properties are present in a Local or Remote
descriptor or multiple values within a group, the order of
preference is descending.

d) Underspecified or overspecified properties within a group of
properties sent by the MGC are requests for the MG to choose one
or more values which it can support for each of those properties.
In case of an overspecified property, the list of values is in
descending order of preference.

Subject to the above rules, subsequent action depends on the values
of the ReserveValue and ReserveGroup properties in LocalControl.

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,
SendRecv, or LoopBack, the MG must be prepared to receive media
encoded according to any of the alternatives included in its
response to the MGC.

If ReserveGroup is False and ReserveValue is False, then the MG
SHOULD apply the following rules to resolve Local and Remote to a
single alternative each:

- 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. The RequestIdentifier is omitted if the
EventsDescriptor is empty (i.e., no events are specified).

Each event in the descriptor contains the Event name, an optional
streamID, an optional KeepActive flag, and optional parameters. The
Event name consists of a Package Name (where the event is defined)
and an EventID. The ALL wildcard may be used for the EventID,
indicating that all events from the specified package have to be
detected. The default streamID is 0, indicating that the event to be
detected is not related to a particular media stream. Events can
have parameters. This allows a single event description to have some
variation in meaning without creating large numbers of individual
events. Further event parameters are defined in the package.

If a digit map completion event is present or implied in the
EventsDescriptor, the EventDM parameter is used to carry either the
name or the value of the associated digit map. See 7.1.14 for
further details.

When an event is processed against the contents of an active Events
Descriptor and found to be present in that descriptor ("recognized"),
the default action of the MG is to send a Notify command to the MGC.
Notification may be deferred if the event is absorbed into the
current dial string of an active digit map (see 7.1.14). Any other
action is for further study. Moreover, event recognition may cause
currently active signals to stop, or may cause the current Events
and/or Signals descriptor to be replaced, as described at the end of

this subclause. Unless the Events Descriptor is replaced by another
Events Descriptor, it remains active after an event has been
recognized.

If the value of the EventBufferControl property equals LockStep,
following detection of such an event, normal handling of events is
suspended. Any event which is subsequently detected and occurs in
the EventBuffer descriptor is added to the end of the EventBuffer (a
FIFO queue), along with the time that it was detected. The MG SHALL
wait for a new EventsDescriptor to be loaded. A new EventsDescriptor
can be loaded either as the result of receiving a command with a new
EventsDescriptor, or by activating an embedded EventsDescriptor.

If EventBufferControl equals Off, the MG continues processing based
on the active EventsDescriptor.

In the case of an embedded EventsDescriptor being activated, the MG
continues event processing based on the newly activated
EventsDescriptor.

NOTE 1 - For purposes of EventBuffer handling, activation of an
embedded EventsDescriptor is equivalent to receipt of a new
EventsDescriptor.

When the MG receives a command with a new EventsDescriptor, one or
more events may have been buffered in the EventBuffer in the MG. The
value of EventBufferControl then determines how the MG treats such
buffered events.

Case 1

If EventBufferControl equals LockStep and the MG receives a new
EventsDescriptor, it will check the FIFO EventBuffer and take the
following actions:

1) If the EventBuffer is empty, the MG waits for detection of events
based on the new EventsDescriptor.

2) If the EventBuffer is non-empty, the MG processes the FIFO queue
starting with the first event:

a) If the event in the queue is in the events listed in the new
EventsDescriptor, the MG acts on the event and removes the
event from the EventBuffer. The time stamp of the Notify shall
be the time the event was actually detected. The MG then waits
for a new EventsDescriptor. While waiting for a new
EventsDescriptor, any events detected that appear in the

EventsBufferDescriptor will be placed in the EventBuffer. When
a new EventsDescriptor is received, the event processing will
repeat from step 1.

b) If the event is not in the new EventsDescriptor, the MG SHALL
discard the event and repeat from step 1.

Case 2

If EventBufferControl equals Off and the MG receives a new
EventsDescriptor, it processes new events with the new
EventsDescriptor.

If the MG receives a command instructing it to set the value of
EventBufferControl to Off, all events in the EventBuffer SHALL be
discarded.

The MG may report several events in a single Transaction as long as
this does not unnecessarily delay the reporting of individual events.

For procedures regarding transmitting the Notify command, refer to
the appropriate annex or Recommendation of the H.248 sub-series for
specific transport considerations.

The default value of EventBufferControl is Off.

NOTE 2 - Since the EventBufferControl property is in the
TerminationStateDescriptor, the MG might receive a command that
changes the EventBufferControl property and does not include an
EventsDescriptor.

Normally, recognition of an event shall cause any active signals to
stop. When KeepActive is specified in the event, the MG shall not
interrupt any signals active on the Termination on which the event is
detected.

An event can include an Embedded Signals descriptor and/or an
Embedded Events descriptor which, if present, replaces the current
Signals/Events descriptor when the event is recognized. It is
possible, for example, to specify that the dial-tone Signal be
generated when an off-hook Event is recognized, or that the dial-tone
Signal be stopped when a digit is recognized. A media gateway
controller shall not send EventsDescriptors with an event both marked
KeepActive and containing an embedded SignalsDescriptor.

Only one level of embedding is permitted. An embedded
EventsDescriptor SHALL NOT contain another embedded EventsDescriptor;
an embedded EventsDescriptor MAY contain an embedded
SignalsDescriptor.

An EventsDescriptor received by a media gateway replaces any previous
Events descriptor. Event notification in process shall complete, and
events detected after the command containing the new EventsDescriptor
executes, shall be processed according to the new EventsDescriptor.

An empty Events Descriptor disables all event recognition and
reporting. An empty EventBuffer Descriptor clears the EventBuffer
and disables all event accumulation in LockStep mode: the only events
reported will be those occurring while an Events Descriptor is
active. If an empty Events Descriptor is activated while the
Termination is operating in LockStep mode, the events buffer is
immediately cleared.

7.1.10 EventBuffer descriptor

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

7.1.11 Signals descriptor

Signals are MG generated media such as tones and announcements as
well as bearer-related signals such as hookswitch. More complex
signals may include a sequence of such simple signals interspersed
with and conditioned upon the receipt and analysis of media or
bearer-related signals. Examples include echoing of received data as
in Continuity Test package. Signals may also request preparation of
media content for future signals.

A SignalsDescriptor is a parameter that contains the set of signals
that the Media Gateway is asked to apply to a Termination. A
SignalsDescriptor contains a number of signals and/or sequential
signal lists. A SignalsDescriptor may contain zero signals and
sequential signal lists. Support of sequential signal lists is
optional.

Signals are defined in packages. Signals shall be named with a
Package name (in which the signal is defined) and a SignalID. No
wildcard shall be used in the SignalID. Signals that occur in a
SignalsDescriptor have an optional StreamID parameter (default is 0,
to indicate that the signal is not related to a particular media
stream), an optional signal type (see below), an optional duration
and possibly parameters defined in the package that defines the

signal. This allows a single signal to have some variation in
meaning, obviating the need to create large numbers of individual
signals.

Finally, the optional parameter "notifyCompletion" allows a MGC to
indicate that it wishes to be notified when the signal finishes
playout. The possible cases are that the signal timed out (or
otherwise completed on its own), that it was interrupted by an event,
that it was halted when a Signals descriptor was replaced, or that it
stopped or never started for other reasons. If the notifyCompletion
parameter is not included in a Signals descriptor, notification is
generated only if the signal stopped or was never started for other
reasons. For reporting to occur, the signal completion event (see
E.1.2) must be enabled in the currently active Events descriptor.

The duration is an integer value that is expressed in hundredths of a
second.

There are three types of signals:

- 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 will stop on its own unless a new Signals
descriptor is applied that causes it to stop; no timeout value is
needed.

If a signal of default type other than TO has its type overridden to
type TO in the Signals descriptor, the duration parameter must be
present.

If the signal type is specified in a SignalsDescriptor, it overrides
the default signal type (see 12.1.4). If duration is specified for
an on/off signal, it SHALL be ignored.

A sequential signal list consists of a signal list identifier and a
sequence of signals to be played sequentially. Only the trailing
element of the sequence of signals in a sequential signal list may be
an on/off signal. The duration of a sequential signal list is the
sum of the durations of the signals it contains.

Multiple signals and sequential signal lists in the same
SignalsDescriptor shall be played simultaneously.

Signals are defined as proceeding from the Termination towards the
exterior of the Context unless otherwise specified in a package.

When the same Signal is applied to multiple Terminations within one
Transaction, the MG should consider using the same resource to
generate these Signals.

Production of a Signal on a Termination is stopped by application of
a new SignalsDescriptor, or detection of an Event on the Termination
(see 7.1.9).

A new SignalsDescriptor replaces any existing SignalsDescriptor. Any
signals applied to the Termination not in the replacement descriptor
shall be stopped, and new signals are applied, except as follows.
Signals present in the replacement descriptor and containing the
KeepActive flag shall be continued if they are currently playing and
have not already completed. If a replacement signal descriptor
contains a signal that is not currently playing and contains the
KeepActive flag, that signal SHALL be ignored. If the replacement
descriptor contains a sequential signal list with the same identifier
as the existing descriptor, then

- 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
any descriptor containing the current values of its properties,
events, signals and statistics even if that descriptor was not
present in the command, or had no underspecified parameters.
Possible items in the Audit descriptor are:

Modem
Mux
Events
Media
Signals
ObservedEvents
DigitMap
Statistics
Packages
EventBuffer

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

7.1.13 ServiceChange descriptor

The ServiceChangeDescriptor contains the following parameters:

. ServiceChangeMethod
. ServiceChangeReason
. ServiceChangeAddress
. ServiceChangeDelay
. ServiceChangeProfile
. ServiceChangeVersion
. ServiceChangeMGCId
. TimeStamp
. Extension

See 7.2.8.

7.1.14 DigitMap descriptor

7.1.14.1 DigitMap definition, creation, modification and deletion

A DigitMap is a dialing plan resident in the Media Gateway used for
detecting and reporting digit events received on a Termination. The
DigitMap descriptor contains a DigitMap name and the DigitMap to be
assigned. A digit map may be preloaded into the MG by management
action and referenced by name in an EventsDescriptor, may be defined
dynamically and subsequently referenced by name, or the actual
digitmap itself may be specified in the EventsDescriptor. It is
permissible for a digit map completion event within an Events
descriptor to refer by name to a DigitMap which is defined by a
DigitMap descriptor within the same command, regardless of the
transmitted order of the respective descriptors.

DigitMaps defined in a DigitMapDescriptor can occur in any of the
standard Termination manipulation Commands of the protocol. A
DigitMap, once defined, can be used on all Terminations specified by
the (possibly wildcarded) TerminationID in such a command. DigitMaps
defined on the root Termination are global and can be used on every
Termination in the MG, provided that a DigitMap with the same name
has not been defined on the given Termination. When a DigitMap is
defined dynamically in a DigitMap descriptor:

- 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.

7.1.14.2 DigitMap Timers

The collection of digits according to a DigitMap may be protected by
three timers, viz. a start timer (T), short timer (S), and long timer
(L).

1) The start timer (T) is used prior to any digits having been
dialed. If the start timer is overridden with the value set to
zero (T=0), then the start timer shall be disabled. This implies
that the MG will wait indefinitely for digits.

2) If the Media Gateway can determine that at least one more digit is
needed for a digit string to match any of the allowed patterns in
the digit map, then the interdigit timer value should be set to a
long (L) duration (e.g., 16 seconds).

3) If the digit string has matched one of the patterns in a digit
map, but it is possible that more digits could be received which
would cause a match with a different pattern, then instead of
reporting the match immediately, the MG must apply the short timer
(S) and wait for more digits.

The timers are configurable parameters to a DigitMap. Default values
of these timers should be provisioned on the MG, but can be
overridden by values specified within the DigitMap.

7.1.14.3 DigitMap Syntax

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

which has been designated in the Events descriptor on the Termination
to which the digit map is being applied. (The mapping between events
and digit map symbols is defined in the documentation for packages
associated with channel-associated signalling systems such as DTMF,
MF, or R2. Digits "0" through "9" MUST be mapped to the
corresponding digit events within the signalling system concerned.
Letters should be allocated in logical fashion, facilitating the use
of range notation for alternative events.)

The letter "x" is used as a wildcard, designating any event
corresponding to symbols in the range "0"-"9". The string may also
contain explicit ranges and, more generally, explicit sets of
symbols, designating alternative events any one of which satisfies
that position of the digit map. Finally, the dot symbol "." stands
for zero or more repetitions of the event selector (event, range of
events, set of alternative events, or wildcard) that precedes it. As
a consequence of the third timing rule above, inter-event timing
while matching a terminal dot symbol uses the short timer by default.

In addition to these event symbols, the string may contain "S" and
"L" inter-event timing specifiers and the "Z" duration modifier. "S"
and "L" respectively indicate that the MG should use the short (S)
timer or the long (L) timer for subsequent events, overriding the
timing rules described above. If an explicit timing specifier is in
effect in one alternative event sequence, but none is given in any
other candidate alternative, the timer value set by the explicit
timing specifier must be used. If all sequences with explicit timing
controls are dropped from the candidate set, timing reverts to the
default rules given above. Finally, if conflicting timing specifiers
are in effect in different alternative sequences, the long timer
shall be used.

A "Z" designates a long duration event: placed in front of the
symbol(s) designating the event(s) which satisfy a given digit
position, it indicates that that position is satisfied only if the
duration of the event exceeds the long-duration threshold. The value
of this threshold is assumed to be provisioned in the MG.

7.1.14.4 DigitMap Completion Event

A digit map is active while the Events descriptor which invoked it is
active and it has not completed. A digit map completes when:

- 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.

7.1.14.5 DigitMap Procedures

Pending completion, successive events shall be processed according to
the following rules:

1) The "current dial string", an internal variable, is initially
empty. The set of candidate alternative event sequences includes
all of the alternatives specified in the digit map.

2) At each step, a timer is set to wait for the next event, based
either on the default timing rules given above or on explicit
timing specified in one or more alternative event sequences. If
the timer expires and a member of the candidate set of
alternatives is fully satisfied, a timeout completion with full
match is reported. If the timer expires and part or none of any
candidate alternative is satisfied, a timeout completion with
partial match is reported.

3) If an event is detected before the timer expires, it is mapped to
a digit string symbol and provisionally added to the end of the
current dial string. The duration of the event (long or not long)
is noted if and only if this is relevant in the current symbol
position (because at least one of the candidate alternative event
sequences includes the "Z" modifier at this position in the
sequence).

4) The current dial string is compared to the candidate alternative
event sequences. If and only if a sequence expecting a
long-duration event at this position is matched (i.e., the event
had long duration and met the specification for this position),
then any alternative event sequences not specifying a long
duration event at this position are discarded, and the current
dial string is modified by inserting a "Z" in front of the symbol
representing the latest event. Any sequence expecting a long-
duration event at this position but not matching the observed
event is discarded from the candidate set. If alternative event
sequences not specifying a long duration event in the given

position remain in the candidate set after application of the
above rules, the observed event duration is treated as irrelevant
in assessing matches to them.

5) If exactly one candidate remains and it has been fully matched, a
completion event is generated indicating an unambiguous match. If
no candidates remain, the latest event is removed from the current
dial string and a completion event is generated indicating full
match if one of the candidates from the previous step was fully
satisfied before the latest event was detected, or partial match
otherwise. The event removed from the current dial string will
then be reported as per the currently active event processing
mechanisms.

6) If no completion event is reported out of step 5, processing
returns to step 2.

7.1.14.6 DigitMap Activation

A digit map is activated whenever a new Event descriptor is applied
to the Termination or embedded Event descriptor is activated, and
that Event descriptor contains a digit map completion event. The
digit map completion event contains an eventDM field in the requested
actions field. Each new activation of a digit map begins at step 1
of the above procedure, with a clear current dial string. Any
previous contents of the current dial string from an earlier
activation are lost.

A digit map completion event that does not contain an eventDM field
in its requested actions field is considered an error. Upon receipt
of such an event in an EventsDescriptor, a MG shall respond with an
error response, including Error 457 - Missing parameter in signal or
event.

7.1.14.7 Interaction Of DigitMap and Event Processing

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

- the events in the package containing the specified digit map
completion event other than the completion event itself are not
individually notified and have no side-effects unless separately
enabled; and

- an event that triggers a partial match completion event is not
recognized and therefore has no side effects until reprocessed
following the recognition of the digit map completion event.

7.1.14.8 Wildcards

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

7.1.14.9 Example

As an example, consider the following dial plan:

0 Local operator

00 Long-distance operator

xxxx Local extension number (starts with 1-7)

8xxxxxxx Local number

#xxxxxxx Off-site extension

*xx Star services

91xxxxxxxxxx Long-distance number

9011 + up to 15 digits International number

If the DTMF detection package described in E.6 is used to collect the
dialed digits, then the dialing plan shown above results in the
following digit map:

(0 00[1-7]xxx8xxxxxxxFxxxxxxxExx91xxxxxxxxxx9011x.)

7.1.15 Statistics descriptor

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

example). The particular statistical properties that are reported
for a given Termination are determined by the Packages realized by
the Termination. By default, statistics are reported when the
Termination is Subtracted from the Context. This behaviour can be
overridden by including an empty AuditDescriptor in the Subtract
command. Statistics may also be returned from the AuditValue
command, or any Add/Move/Modify command using the Audit descriptor.

Statistics are cumulative; reporting Statistics does not reset them.
Statistics are reset when a Termination is Subtracted from a Context.

7.1.16 Packages descriptor

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

7.1.17 ObservedEvents descriptor

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

7.1.18 Topology descriptor

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

The Topology descriptor occurs before the commands in an action. It
is possible to have an action containing only a Topology descriptor,
provided that the Context to which the action applies already exists.

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.

CHOOSE wildcards may be used in T1 and T2 as well, under the
following restrictions:

- the action (see clause 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.

If a termination is not mentioned within a Topology Descriptor, any
topology associated with it remains unchanged. If, however, a new
termination is added into a context its association with the other
terminations within the context defaults to bothway, unless a
Topology Descriptor is given to change this (e.g., if T3 is added to
a context with T1 and T2 with topology (T3, T1, oneway) it will be
connected bothway to T2).

Figure 7 and the table following it show some examples of the effect
of including topology descriptors in actions. In these examples it
is assumed that the topology descriptors are applied in sequence.

+------------------+ +------------------+ +------------------+
+----+ +----+ +----+
T2 T2 T2
+----+ +----+ +----+
^ ^ ^ ^

+--+ +--+ +---+ +--+

v v v
+----+ +----+ +----+ +----+ +----+ +----+
T1 <--> T3 T1 <--> T3 T1 <--> T3
+----+ +----+ +----+ +----+ +----+ +----+
+------------------+ +------------------+ +------------------+
1. No Topology Desc. 2. T1, T2, Isolate 3. T3, T2, Oneway

+------------------+ +------------------+ +------------------+
+----+ +----+ +----+
T2 T2 T2
+----+ +----+ +----+
^ ^ ^

+--+ +---+ +--+ +--+

v v v v
+----+ +----+ +----+ +----+ +----+ +----+
T1 <--> T3 T1 <--> T3 T1 <--> T3
+----+ +----+ +----+ +----+ +----+ +----+
+------------------+ +------------------+ +------------------+
4. T2, T3 oneway 5. T2, T3 bothway 6. T1, T2 bothway

Note: the direction of the arrow indicates the direction of flow.

Figure 7: Example topologies

Topology Description

1 No topology descriptors When no topology descriptors are
included, all Terminations have a
bothway connection to all other
Terminations.

2 T1, T2 Isolate Removes the connection between T1 and
T2. T3 has a bothway connection with
both T1 and T2. T1 and T2 have bothway
connection to T3.

3 T3, T2 oneway A oneway connection from T3 to T2 (i.e.,
T2 receives media flow from T3). A
bothway connection between T1 and T3.

4 T2, T3 oneway A oneway connection between T2 to T3.
T1 and T3 remain bothway connected.

5 T2, T3 bothway T2 is bothway connected to T3. This
results in the same as 2.

6 T1, T2 bothway (T2, T3 All Terminations have a bothway
bothway and T1, T3 connection to all other Terminations.
bothway may be implied or
explicit).

A oneway connection must be implemented in such a way that the other
Terminations in the Context are not aware of the change in topology.

7.1.19 Error Descriptor

If a responder encounters an error when processing a transaction
request, it must include an error descriptor in its response. A
Notify request may contain an error descriptor as well.

An error descriptor consists of an IANA-registered error code,
optionally accompanied by an error text. H.248.8 contains a list of
valid error codes and error descriptions.

An error descriptor shall be specified at the "deepest level" that is
semantically appropriate for the error being described and that is
possible given any parsing problems with the original request. An
error descriptor may refer to a syntactical construct other than
where it appears. For example, Error descriptor 422 - Syntax Error
in Action, could appear within a command even though it refers to the
larger construct - the action - and not the particular command within
which it appears.

7.2 Command Application Programming Interface

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

specified in later subclauses. The order of parameters to commands
is not fixed. Descriptors may appear as parameters to commands in
any order. The descriptors SHALL be processed in the order in which
they appear.

Any reply to a command may contain an error descriptor; the API does
not specifically show this.

All parameters enclosed by square brackets ([. . .]) are considered
optional.

7.2.1 Add

The Add Command adds a Termination to a Context.

TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Add( TerminationID
[, MediaDescriptor]
[, ModemDescriptor]
[, MuxDescriptor]
[, EventsDescriptor]
[, EventBufferDescriptor]
[, SignalsDescriptor]
[, DigitMapDescriptor]
[, AuditDescriptor]
)

The TerminationID specifies the Termination to be added to the
Context. The Termination is either created, or taken from the null
Context. If a CHOOSE wildcard is used in the TerminationID, the
selected TerminationID will be returned. Wildcards may be used in an
Add, but such usage would be unusual. If the wildcard matches more
than one TerminationID, all possible matches are attempted, with
results reported for each one. The order of attempts when multiple
TerminationIDs match is not specified.

The optional MediaDescriptor describes all media streams.

The optional ModemDescriptor and MuxDescriptor specify a modem and
multiplexer if applicable. For convenience, if a Multiplex
descriptor is present in an Add command and lists any Terminations
that are not currently in the Context, such Terminations are added to
the Context as if individual Add commands listing the Terminations
were invoked. If an error occurs on such an implied Add, error 471 -
Implied Add for Multiplex failure shall be returned and further
processing of the command shall cease.

The EventsDescriptor parameter is optional. If present, it provides
the list of events that should be detected on the Termination.

The EventBufferDescriptor parameter is optional. If present, it
provides the list of events that the MG is requested to detect and
buffer when EventBufferControl equals LockStep.

The SignalsDescriptor parameter is optional. If present, it provides
the list of signals that should be applied to the Termination.

The DigitMapDescriptor parameter is optional. If present, it defines
a DigitMap definition that may be used in an EventsDescriptor.

The AuditDescriptor is optional. If present, the command will return
descriptors as specified in the AuditDescriptor.

All descriptors that can be modified could be returned by MG if a
parameter was underspecified or overspecified. ObservedEvents,
Statistics, and Packages, and the EventBuffer descriptors are
returned only if requested in the AuditDescriptor.

Add SHALL NOT be used on a Termination with a serviceState of
"OutofService".

7.2.2 Modify

The Modify Command modifies the properties of a Termination.

TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]

Modify( TerminationID
[, MediaDescriptor]
[, ModemDescriptor]
[, MuxDescriptor]
[, EventsDescriptor]
[, EventBufferDescriptor]
[, SignalsDescriptor]
[, DigitMapDescriptor]
[, AuditDescriptor]
)

The TerminationID may be specific if a single Termination in the
Context is to be modified. Use of wildcards in the TerminationID may
be appropriate for some operations. If the wildcard matches more
than one TerminationID, all possible matches are attempted, with
results reported for each one. The order of attempts when multiple
TerminationIDs match is not specified. The CHOOSE option is an
error, as the Modify command may only be used on existing
Terminations.

For convenience, if a Multiplex Descriptor is present in a Modify
command, then:

- if the new Multiplex Descriptor lists any Terminations that are
not currently in the Context, such Terminations are added to the
context as if individual commands listing the Terminations were
invoked.

- if any Terminations listed previously in the Multiplex Descriptor
are no longer present in the new Multiplex Descriptor, they are
subtracted from the context as if individual Subtract commands
listing the Terminations were invoked.

The remaining parameters to Modify are the same as those to Add.
Possible return values are the same as those to Add.

7.2.3 Subtract

The Subtract Command disconnects a Termination from its Context and
returns statistics on the Termination's participation in the Context.

TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]

[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Subtract(TerminationID
[, AuditDescriptor]
)

TerminationID in the input parameters represents the Termination that
is being subtracted. The TerminationID may be specific or may be a
wildcard value indicating that all (or a set of related) Terminations
in the Context of the Subtract Command are to be subtracted. If the
wildcard matches more than one TerminationID, all possible matches
are attempted, with results reported for each one. The order of
attempts when multiple TerminationIDs match is not specified.

The use of CHOOSE in the TerminationID is an error, as the Subtract
command may only be used on existing Terminations.

ALL may be used as the ContextID as well as the TerminationId in a
Subtract, which would have the effect of deleting all Contexts,
deleting all ephemeral Terminations, and returning all physical
Terminations to Null Context. Subtract of a termination from the
Null Context is not allowed.

For convenience, if a multiplexing Termination is the object of a
Subtract command, then any bearer Terminations listed in its
Multiplex Descriptor are subtracted from the context as if individual
Subtract commands listing the Terminations were invoked.

By default, the Statistics parameter is returned to report
information collected on the Termination or Terminations specified in
the Command. The information reported applies to the Termination's
or Terminations' existence in the Context from which it or they are
being subtracted.

The AuditDescriptor is optional. If present, the command will return
only those descriptors as specified in the AuditDescriptor, which may
be empty. If omitted, the Statistics descriptor is returned, by
default. Possible return values are the same as those to Add.

When a provisioned Termination is Subtracted from a Context, its
property values shall revert to:

- 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]
[, EventBufferDescriptor]
[, SignalsDescriptor]
[, DigitMapDescriptor]
[, AuditDescriptor]
)

The TerminationID specifies the Termination to be moved. It may be
wildcarded, but CHOOSE shall not be used in the TerminationID. If
the wildcard matches more than one TerminationID, all possible
matches are attempted, with results reported for each one. The order
of attempts when multiple TerminationIDs match is not specified. The
Context to which the Termination is moved is indicated by the target
ContextId in the Action. If the last remaining Termination is moved
out of a Context, the Context is deleted.

The Move command does not affect the properties of the Termination on
which it operates, except those properties explicitly modified by
descriptors included in the Move command. The AuditDescriptor with
the Statistics option, for example, would return statistics on the
Termination just prior to the Move. Possible descriptors returned
from Move are the same as for Add.

For convenience, if a multiplexing Termination is the object of a
Move command, then any bearer Terminations listed in its Multiplex
Descriptor are also moved as if individual Move commands listing the
Terminations were invoked.

Move SHALL NOT be used on a Termination with a serviceState of
"OutofService".

7.2.5 AuditValue

The AuditValue Command returns the current values of properties,
events, signals and statistics associated with Terminations.

TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
AuditValue(TerminationID,
AuditDescriptor
)

TerminationID may be specific or wildcarded. If the wildcard matches
more than one TerminationID, all possible matches are attempted, with
results reported for each one. The order of attempts when multiple
TerminationIDs match is not specified. If a wildcarded response is
requested, only one command return is generated, with the contents
containing the union of the values of all Terminations matching the
wildcard. This convention may reduce the volume of data required to
audit a group of Terminations. Use of CHOOSE is an error.

The appropriate descriptors, with the current values for the
Termination, are returned from AuditValue. Values appearing in
multiple instances of a descriptor are defined to be alternate values
supported, with each parameter in a descriptor considered
independent.

ObservedEvents returns a list of events in the EventBuffer. If the
ObservedEventsDescriptor is audited while a DigitMap is active, the
returned ObservedEvents descriptor also includes a digit map
completion event that shows the current dial string but does not show
a Termination method.

EventBuffer returns the set of events and associated parameter values
currently enabled in the EventBufferDescriptor. PackagesDescriptor
returns a list of packages realized by the Termination.
DigitMapDescriptor returns the name or value of the current DigitMap
for the Termination. DigitMap requested in an AuditValue command
with TerminationID ALL returns all DigitMaps in the gateway.
Statistics returns the current values of all statistics being kept on
the Termination. Specifying an empty Audit descriptor results in
only the TerminationID being returned. This may be useful to get a
list of TerminationIDs when used with wildcard. Annexes A and B
provide a special syntax for presenting such a list in condensed
form, such that the AuditValue command tag does not have to be
repeated for each TerminationID.

AuditValue results depend on the Context, viz. specific, null, or
wildcarded. (Note that ContextID ALL does not include the null
Context.) The TerminationID may be specific, or wildcarded.

The following are examples of what is returned in case the context
and/or the termination is wildcarded and a wildcarded response has
been specified.

Assume that the gateway has 4 terminations: t1/1, t1/2, t2/1 and
t2/2. Assume that terminations t1/* have implemented packages aaa
and bbb and that terminations t2/* have implemented packages ccc and
ddd. Assume that Context 1 has t1/1 and t2/1 in it and that Context
2 has t1/2 and t2/2 in it.

The command:

Context=1{AuditValue=t1/1{Audit{Packages}}}

Returns:

Context=1{AuditValue=t1/1{Packages{aaa,bbb}}}

The command:

Context=*{AuditValue=t2/*{Audit{Packages}}}

Returns:

Context=1{AuditValue=t2/1{Packages{ccc,ddd}}},
Context=2{AuditValue=t2/2{Packages{ccc,ddd}}}

The command:

Context=*{W-AuditValue=t1/*{Audit{Packages}}}

Returns:

Context=*{W-AuditValue=t1/*{Packages{aaa,bbb}}}

Note: A wildcard response may also be used for other commands such as
Subtract.

The following illustrates other information that can be obtained with
the AuditValue Command:

ContextID TerminationID Information Obtained

Specific wildcard Audit of matching Terminations in a Context

Specific specific Audit of a single Termination in a Context

Null Root Audit of Media Gateway state and events

Null wildcard Audit of all matching Terminations in the
null Context

Null specific Audit of a single Termination outside of any
Context

All wildcard Audit of all matching Terminations and the
Context to which they are associated

All Root List of all ContextIds (the ContextID list
should be returned by using multiple action
replies, each containing a ContextID from
the list)

All Specific (Non-null) ContextID in which the
Termination currently exists

7.2.6 AuditCapabilities

The AuditCapabilities Command returns the possible values of
properties, events, signals and statistics associated with
Terminations.

TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
AuditCapabilities(TerminationID,
AuditDescriptor
)

The appropriate descriptors, with the possible values for the
Termination are returned from AuditCapabilities. Descriptors may be
repeated where there are multiple possible values. If a wildcarded
response is requested, only one command return is generated, with the
contents containing the union of the values of all Terminations
matching the wildcard. This convention may reduce the volume of data
required to audit a group of Terminations.

Interpretation of what capabilities are requested for various values
of ContextID and TerminationID is the same as in AuditValue.

The EventsDescriptor returns the list of possible events on the
Termination together with the list of all possible values for the
EventsDescriptor Parameters. EventBufferDescriptor returns the same
information as EventsDescriptor. The SignalsDescriptor returns the
list of possible signals that could be applied to the Termination
together with the list of all possible values for the Signals
Parameters. StatisticsDescriptor returns the names of the statistics
being kept on the termination. ObservedEventsDescriptor returns the
names of active events on the Termination. DigitMap and Packages are
not legal in AuditCapability.

The following illustrates other information that can be obtained with
the AuditCapabilties Command:

ContextID TerminationID Information Obtained

Specific wildcard Audit of matching Terminations in a Context

Specific specific Audit of a single Termination in a Context

Null Root Audit of MG state and events

Null wildcard Audit of all matching Terminations in the
Null Context

Null specific Audit of a single Termination outside of any
Context

All wildcard Audit of all matching Terminations and the
Context to which they are associated

All Root Same as for AuditValue

All Specific Same as for AuditValue

7.2.7 Notify

The Notify Command allows the Media Gateway to notify the Media
Gateway Controller of events occurring within the Media Gateway.

TerminationID
Notify(TerminationID,
ObservedEventsDescriptor,
[ErrorDescriptor]
)

The TerminationID parameter specifies the Termination issuing the
Notify Command. The TerminationID shall be a fully qualified name.

The ObservedEventsDescriptor contains the RequestID and a list of
events that the Media Gateway detected in the order that they were
detected. Each event in the list is accompanied by parameters
associated with the event and optionally an indication of the time
that the event was detected. Procedures for sending Notify commands
with RequestID equal to 0 are for further study.

Notify Commands with RequestID not equal to 0 shall occur only as the
result of detection of an event specified by an Events descriptor
which is active on the Termination concerned.

The RequestID returns the RequestID parameter of the EventsDescriptor
that triggered the Notify Command. It is used to correlate the
notification with the request that triggered it. The events in the
list must have been requested via the triggering EventsDescriptor or
embedded events descriptor unless the RequestID is 0 (which is for
further study).

The ErrorDescriptor may be sent in the Notify Command as a result of
Error 518 - Event buffer full.

7.2.8 ServiceChange

The ServiceChange Command allows the Media Gateway to notify the
Media Gateway Controller that a Termination or group of Terminations
is about to be taken out of service or has just been returned to
service. The Media Gateway Controller may indicate that
Termination(s) shall be taken out of or returned to service. The
Media Gateway may notify the MGC that the capability of a Termination
has changed. It also allows a MGC to hand over control of a MG to
another MGC.

TerminationID,

[ServiceChangeDescriptor]
ServiceChange ( TerminationID,
ServiceChangeDescriptor
)

The TerminationID parameter specifies the Termination(s) that are
taken out of or returned to service. Wildcarding of Termination
names is permitted, with the exception that the CHOOSE mechanism
shall not be used. Use of the "Root" TerminationID indicates a
ServiceChange affecting the entire Media Gateway.

The ServiceChangeDescriptor contains the following parameters as
required:

- 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 on the
Termination(s) affected by the serviceChange command. The MG
should set Termination serviceState at the expiry of
ServiceChangeDelay or the removal of the Termination from an
active Context (whichever is first), to "out of service".

2) Forced - indicates that the specified Terminations were taken
abruptly out of service and any established connections associated
with them may be lost. For non-Root terminations, the MGC is
responsible for cleaning up the Context (if any) with which the
failed Termination is associated. At a minimum the Termination
shall be subtracted from the Context. The Termination
serviceState should be "out of service". For the root
termination, the MGC can assume that all connections are lost on
the MG and thus can consider that all the terminations have been
subtracted.

3) Restart - indicates that service will be restored on the specified
Terminations after expiration of the ServiceChangeDelay. The
serviceState should be set to "inService" upon expiry of
ServiceChangeDelay.

4) Disconnected - always applied with the Root TerminationID,
indicates that the MG lost communication with the MGC, but it was
subsequently restored to the same MGC (possibly after trying other
MGCs on a pre-provisioned list). Since MG state may have changed,
the MGC may wish to use the Audit command to resynchronize its
state with the MG's.

5) Handoff - sent from the MGC to the MG, this reason indicates that
the MGC is going out of service and a new MGC association must be
established. Sent from the MG to the MGC, this indicates that the
MG is attempting to establish a new association in accordance with
a Handoff received from the MGC with which it was previously
associated.

6) Failover - sent from MG to MGC to indicate the primary MG is out
of service and a secondary MG is taking over. This serviceChange
method is also sent from the MG to the MGC when the MG detects
that MGC has failed.

7) Another value whose meaning is mutually understood between the MG
and the MGC.

The ServiceChangeReason parameter specifies the reason why the
ServiceChange has or will occur. It consists of an alphanumeric
token (IANA registered) and, optionally, an explanatory string.

The optional ServiceChangeAddress parameter specifies the address
(e.g., IP port number for IP networks) to be used for subsequent
communications. It can be specified in the input parameter
descriptor or the returned result descriptor. ServiceChangeAddress
and ServiceChangeMgcId parameters must not both be present in the
ServiceChangeDescriptor or the ServiceChangeResultDescriptor. The
ServiceChangeAddress provides an address to be used within the
Context of the association currently being negotiated, while the
ServiceChangeMgcId provides an alternate address where the MG should
seek to establish another association. Note that the use of
ServiceChangeAddress is not encouraged. MGCs and MGs must be able to
cope with the ServiceChangeAddress being either a full address or
just a port number in the case of TCP transports.

The optional ServiceChangeDelay parameter is expressed in seconds.
If the delay is absent or set to zero, the delay value should be
considered to be null. In the case of a "graceful"
ServiceChangeMethod, a null delay indicates that the Media Gateway
Controller should wait for the natural removal of existing
connections and should not establish new connections. For "graceful"
only, a null delay means the MG must not set serviceState "out of
service" until the Termination is in the null Context.

The optional ServiceChangeProfile parameter specifies the Profile (if
any) of the protocol supported. The ServiceChangeProfile includes
the version of the profile supported.

The optional ServiceChangeVersion parameter contains the protocol
version and is used if protocol version negotiation occurs (see
11.3).

The optional TimeStamp parameter specifies the actual time as kept by
the sender. As such, it is not necessarily absolute time according
to, for example, a local time zone - it merely establishes an
arbitrary starting time against which all future timestamps
transmitted by a sender during this association shall be compared.
It can be used by the responder to determine how its notion of time
differs from that of its correspondent. TimeStamp is sent with a
precision of hundredths of a second.

The optional Extension parameter may contain any value whose meaning
is mutually understood by the MG and MGC.

A ServiceChange Command specifying the "Root" for the TerminationID
and ServiceChangeMethod equal to Restart is a registration command by
which a Media Gateway announces its existence to the Media Gateway
Controller. The Media Gateway may also announce a registration
command by specifying the "Root" for the TerminationID and
ServiceChangeMethod equal to Failover when the MG detects MGC
failures. The Media Gateway is expected to be provisioned with the
name of one primary and optionally some number of alternate Media
Gateway Controllers. Acknowledgement of the ServiceChange Command
completes the registration process, except when the MGC has returned
an alternative ServiceChangeMgcId as described in the following
paragraph. The MG may specify the transport ServiceChangeAddress to
be used by the MGC for sending messages in the ServiceChangeAddress
parameter in the input ServiceChangeDescriptor. The MG may specify
an address in the ServiceChangeAddress parameter of the ServiceChange
request, and the MGC may also do so in the ServiceChange reply. In
either case, the recipient must use the supplied address as the
destination for all subsequent transaction requests within the
association. At the same time, as indicated in clause 9, transaction
replies and pending indications must be sent to the address from
which the corresponding requests originated. This must be done even
if it implies extra messaging because commands and responses cannot
be packed together. The TimeStamp parameter shall be sent with a
registration command and its response.

The Media Gateway Controller may return a ServiceChangeMgcId
parameter that describes the Media Gateway Controller that should
preferably be contacted for further service by the Media Gateway. In
this case the Media Gateway shall reissue the ServiceChange command
to the new Media Gateway Controller. The MGC specified in a
ServiceChangeMgcId, if provided, shall be contacted before any
further alternate MGCs. On a HandOff message from MGC to MG, the
ServiceChangeMgcId is the new MGC that will take over from the
current MGC.

The return from ServiceChange is empty except when the Root
terminationID is used. In that case it includes the following
parameters as required:

- ServiceChangeAddress, if the responding MGC wishes to specify a
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 13.3.

900 Service Restored
901 Cold Boot
902 Warm Boot
903 MGC Directed Change
904 Termination malfunctioning
905 Termination taken out of service
906 Loss of lower layer connectivity (e.g., downstream sync)
907 Transmission Failure
908 MG Impending Failure
909 MGC Impending Failure
910 Media Capability Failure
911 Modem Capability Failure
912 Mux Capability Failure
913 Signal Capability Failure
914 Event Capability Failure
915 State Loss

7.2.9 Manipulating and Auditing Context Attributes

The commands of the protocol as discussed in the preceding subclauses
apply to Terminations. This subclause specifies how Contexts are
manipulated and audited.

Commands are grouped into actions (see clause 8). An action applies
to one Context. In addition to commands, an action may contain
Context manipulation and auditing instructions.

An action request sent to a MG may include a request to audit
attributes of a Context. An action may also include a request to
change the attributes of a Context.

The Context properties that may be included in an action reply are
used to return information to a MGC. This can be information
requested by an audit of Context attributes or details of the effect
of manipulation of a Context.

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
7.1.8.

7.3 Command Error Codes

Errors consist of an IANA registered error code and an explanatory
string. Sending the explanatory string is optional. Implementations
are encouraged to append diagnostic information to the end of the
string.

When a MG reports an error to a MGC, it does so in an error
descriptor. An error descriptor consists of an error code and
optionally the associated explanatory string.

H.248.8 contains the error codes supported by Recommendations in the
H.248 sub-series.

8 Transactions

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

+----------------------------------------------------------+
Transaction x
+----------------------------------------------------+
Action 1
+---------+ +---------+ +---------+ +---------+
Command Command Command Command
1 2 3 4
+---------+ +---------+ +---------+ +---------+
+----------------------------------------------------+

+----------------------------------------------------+
Action 2
+---------+
Command
1
+---------+
+----------------------------------------------------+

+----------------------------------------------------+
Action 3
+---------+ +---------+ +---------+
Command Command Command
1 2 3
+---------+ +---------+ +---------+
+----------------------------------------------------+
+----------------------------------------------------------+

Figure 8: Transactions, Actions and Commands

Transactions are presented as TransactionRequests. Corresponding
responses to a TransactionRequest are received in a single reply,
possibly preceded by a number of TransactionPending messages (see
8.2.3).

Transactions guarantee ordered Command processing. That is, Commands
within a Transaction are executed sequentially. Ordering of
Transactions is NOT guaranteed - transactions may be executed in any
order, or simultaneously.

At the first failing Command in a Transaction, processing of the
remaining Commands in that Transaction stops. If a command contains
a wildcarded TerminationID, the command is attempted with each of the
actual TerminationIDs matching the wildcard. A response within the
TransactionReply is included for each matching TerminationID, even if
one or more instances generated an error. If any TerminationID
matching a wildcard results in an error when executed, any commands
following the wildcarded command are not attempted.

Commands may be marked as "Optional" which can override this
behaviour - if a command marked as Optional results in an error,
subsequent commands in the Transaction will be executed. If a
command fails, the MG shall as far as possible restore the state that
existed prior to the attempted execution of the command before
continuing with command processing.

A TransactionReply includes the results for all of the Commands in
the corresponding TransactionRequest. The TransactionReply includes
the return values for the Commands that were executed successfully,
and the Command and error descriptor for any Command that failed.

TransactionPending is used to periodically notify the receiver that a
Transaction has not completed yet, but is actively being processed.

Applications SHOULD implement an application level timer per
transaction. Expiration of the timer should cause a retransmission
of the request. Receipt of a Reply should cancel the timer. Receipt
of Pending should restart the timer.

8.1 Common parameters

8.1.1 Transaction Identifiers

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

8.1.2 Context Identifiers

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

The CHOOSE wildcard is used to request that the Media Gateway create
a new Context.

The MGC may use the ALL wildcard to address all Contexts on the MG.
The null Context is not included when the ALL wildcard is used.

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

8.2 Transaction Application Programming Interface

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

8.2.1 TransactionRequest

The TransactionRequest is invoked by the sender. There is one
Transaction per request invocation. A request contains one or more
Actions, each of which specifies its target Context and one or more
Commands per Context.

TransactionRequest(TransactionId {
ContextID {Command ... Command},
. . .
ContextID {Command ... Command } })

The TransactionID parameter must specify a value for later
correlation with the TransactionReply or TransactionPending response
from the receiver.

The ContextID parameter must specify a value to pertain to all
Commands that follow up to either the next specification of a
ContextID parameter or the end of the TransactionRequest, whichever
comes first.

The Command parameter represents one of the Commands mentioned in 7.2
(Command Application Programming Interface).

8.2.2 TransactionReply

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

A TransactionRequest has been processed:

- when all actions in that TransactionRequest have been processed;
or

- when an error is encountered in processing that
TransactionRequest, except when the error is in an optional
command.

A command has been processed when all descriptors in that command
have been processed.

A SignalsDescriptor is considered to have been processed when it has
been established that the descriptor is syntactically valid, the
requested signals are supported and they have been queued to be
applied.

An EventsDescriptor or EventBufferDescriptor is considered to have
been processed when it has been established that the descriptor is
syntactically valid, the requested events can be observed, any
embedded signals can be generated, any embedded events can be
detected, and the MG has been brought into a state in which the
events will be detected.

TransactionReply(TransactionID {
ContextID { Response ... Response },
. . .
ContextID { Response ... Response } })

The TransactionID parameter must be the same as that of the
corresponding TransactionRequest.

The ContextID parameter must specify a value to pertain to all
Responses for the action. The ContextID may be specific, all or
null.

Each of the Response parameters represents a return value as
mentioned in 7.2, or an error descriptor if the command execution
encountered an error. Commands after the point of failure are not
processed and, therefore, Responses are not issued for them.

An exception to this occurs if a command has been marked as optional
in the Transaction request. If the optional command generates an
error, the transaction still continues to execute, so the Reply
would, in this case, have Responses after an Error.

Section 7.1.19 Error Descriptor specifies the generation of error
descriptors. The text below discusses several individual cases.

If the receiver encounters an error in processing a ContextID, the
requested Action response will consist of the Context ID and a single
error descriptor, 422 - Syntax Error in Action.

If the receiver encounters an error such that it cannot determine a
legal Action, it will return a TransactionReply consisting of the
TransactionID and a single error descriptor, 422 - Syntax Error in
Action. If the end of an action cannot be reliably determined but
one or more commands can be parsed, it will process them and then
send 422 - Syntax Error in Action as the last action for the
transaction. If the receiver encounters an error such that is cannot
determine a legal Transaction, it will return a TransactionReply with
a null TransactionID and a single error descriptor (403 - Syntax
Error in TransactionRequest).

If the end of a transaction cannot be reliably determined and one or
more Actions can be parsed, it will process them and then return 403
- Syntax Error in Transaction as the last action reply for the
transaction. If no Actions can be parsed, it will return 403 -
Syntax Error in TransactionRequest as the only reply.

If the terminationID cannot be reliably determined, it will send 442
- Syntax Error in Command as the action reply.

If the end of a command cannot be reliably determined, it will return
442 - Syntax Error in Command as the reply to the last action it can
parse.

8.2.3 TransactionPending

The receiver invokes the TransactionPending. A TransactionPending
indicates that the Transaction is actively being processed, but has
not been completed. It is used to prevent the sender from assuming
the TransactionRequest was lost where the Transaction will take some
time to complete.

TransactionPending(TransactionID { } )

The TransactionID parameter must be the same as that of the
corresponding TransactionRequest. A property of root
(normalMGExecutionTime) is settable by the MGC to indicate the
interval within which the MGC expects a response to any transaction
from the MG. Another property (normalMGCExecutionTime) is settable
by the MGC to indicate the interval within which the MG should expect
a response to any transaction from the MGC. Senders may receive more
than one TransactionPending for a command. If a duplicate request is

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

8.3 Messages

Multiple Transactions can be concatenated into a Message. Messages
have a header, which includes the identity of the sender. The
Message Identifier (MID) of a message is set to a provisioned name
(e.g., domain address/domain name/device name) of the entity
transmitting the message. Domain name is a suggested default. An
H.248.1 entity (MG/MGC) must consistently use the same MID in all
messages it originates for the duration of control association with
the peer (MGC/MG).

Every Message contains a Version Number identifying the version of
the protocol the message conforms to. Versions consist of one or two
digits, beginning with version 1 for the present version of the
protocol.

The transactions in a message are treated independently. There is no
order implied; there is no application or protocol acknowledgement of
a message. A message is essentially a transport mechanism. For
example, message X containing transaction requests A, B, and C may be
responded to with message Y containing replies to A and C and message
Z containing the reply to B. Likewise, message L containing request
D and message M containing request E may be responded to with message
N containing replies to both D and E.

9 Transport

The transport mechanism for the protocol should allow the reliable
transport of transactions between a MGC and MG. The transport shall
remain independent of what particular commands are being sent and
shall be applicable to all application states. There are several
transports defined for the protocol, which are defined in Annexes to
this RFCand other Recommendations of the H.248
sub-series. Additional Transports may be defined as additional

Recommendations of the H.248 sub-series. For transport of the
protocol over IP, MGCs shall implement both TCP and UDP/ALF, a MG
shall implement TCP or UDP/ALF or both.

The MG is provisioned with a name or address (such as DNS name or IP
address) of a primary and zero or more secondary MGCs (see 7.2.8)
that is the address the MG uses to send messages to the MGC. If TCP
or UDP is used as the protocol transport and the port to which the
initial ServiceChange request is to be sent is not otherwise known,

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

9.1 Ordering of Commands

This RFCdoes 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
clause 8).

1) When a Media Gateway handles several Terminations, commands
pertaining to the different Terminations may be sent in parallel,
for example following a model where each Termination (or group of
Terminations) is controlled by its own process or its own thread.

2) On a Termination, there should normally be at most one outstanding
command (Add or Modify or Move), unless the outstanding commands
are in the same transaction. However, a Subtract command may be
issued at any time. In consequence, a Media Gateway may sometimes
receive a Modify command that applies to a previously subtracted
Termination. Such commands should be ignored, and an error code
should be returned.

3) For transports that do not guarantee in-sequence delivery of
messages (i.e., UDP), there should normally be on a given
Termination at most one outstanding Notify command at any time.

4) In some cases, an implicitly or explicitly wildcarded Subtract
command that applies to a group of Terminations may step in front
of a pending Add command. The Media Gateway Controller should
individually delete all Terminations for which an Add command was
pending at the time of the global Subtract command. Also, new Add
commands for Terminations named by the wildcarding (or implied in
a Multiplex descriptor) should not be sent until the wildcarded
Subtract command is acknowledged.

5) AuditValue and AuditCapability are not subject to any sequencing.

6) ServiceChange shall always be the first command sent by a MG as
defined by the restart procedure. Any other command or response
must be delivered after this ServiceChange command.

These rules do not affect the command responder, which should always
respond to commands.

9.2 Protection against Restart Avalanche

In the event that a large number of Media Gateways are powered on
simultaneously and they were to all initiate a ServiceChange
transaction, the Media Gateway Controller would very likely be
swamped, leading to message losses and network congestion during the
critical period of service restoration. In order to prevent such
avalanches, the following behaviour is suggested:

1) When a Media Gateway is powered on, it should initiate a restart
timer to a random value, uniformly distributed between 0 and a
maximum waiting delay (MWD). Care should be taken to avoid
synchronicity of the random number generation between multiple
Media Gateways that would use the same algorithm.

2) The Media Gateway should then wait for either the end of this
timer or the detection of a local user activity, such as for
example an off-hook transition on a residential Media Gateway.

3) When the timer elapses, or when an activity is detected, the Media
Gateway should initiate the restart procedure.

The restart procedure simply requires the MG to guarantee that the
first message that the Media Gateway Controller sees from this MG is
a ServiceChange message informing the Media Gateway Controller about
the restart.

NOTE - The value of MWD is a configuration parameter that depends
on the type of the Media Gateway. The following reasoning may be
used to determine the value of this delay on residential gateways.

Media Gateway Controllers are typically dimensioned to handle the
peak hour traffic load, during which, in average, 10% of the lines
will be busy, placing calls whose average duration is typically 3
minutes. The processing of a call typically involves 5 to 6 Media
Gateway Controller transactions between each Media Gateway and the
Media Gateway Controller. This simple calculation shows that the
Media Gateway Controller is expected to handle 5 to 6 transactions
for each Termination, every 30 minutes on average, or, to put it
otherwise, about one transaction per Termination every 5 to 6 minutes
on average. This suggests that a reasonable value of MWD for a
residential gateway would be 10 to 12 minutes. In the absence of
explicit configuration, residential gateways should adopt a value of
600 seconds for MWD.

The same reasoning suggests that the value of MWD should be much
shorter for trunking gateways or for business gateways, because they
handle a large number of Terminations, and also because the usage
rate of these Terminations is much higher than 10% during the peak
busy hour, a typical value being 60%. These Terminations, during the
peak hour, are this expected to contribute about one transaction per
minute to the Media Gateway Controller load. A reasonable algorithm
is to make the value of MWD per "trunk" Termination six times shorter
than the MWD per residential gateway, and also inversely proportional
to the number of Terminations that are being restarted. For example
MWD should be set to 2.5 seconds for a gateway that handles a T1
line, or to 60 milliseconds for a gateway that handles a T3 line.

10 Security Considerations

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

10.1 Protection of Protocol Connections

A security mechanism is clearly needed to prevent unauthorized
entities from using the protocol defined in this RFCfor 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 [RFC
2406] 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 RFCemploying 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 RFCwhere the underlying
network implementation does not support IPsec.

As an interim solution, an optional AH header is defined within the
H.248.1 protocol header. The header fields are exactly those of the
SPI, SEQUENCE NUMBER and DATA fields as defined in [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 all the transactions (concatenated) in the
message prepended by a synthesized IP header consisting of a 32-bit
source IP address, a 32-bit destination address and a 16-bit UDP
destination port encoded as 20 hex digits. When the interim AH
mechanism is employed when TCP is the transport Layer, the UDP Port
above becomes the TCP port, and all other operations are the same.

Implementations of the H.248.1 protocol SHALL implement IPsec where
the underlying operating system and the transport network supports
IPsec. Implementations of the protocol using IPv4 SHALL implement
the interim AH scheme. However, this interim scheme SHALL NOT be
used when the underlying network layer supports IPsec. IPv6
implementations are assumed to support IPsec and SHALL NOT use the
interim AH scheme.

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 round trip, and
leaves us with a dilemma: either allow the call to proceed without
waiting for the round trip to complete, and risk for example,
"clipping" a remote announcement, or wait for the full round trip
and settle for slower call-set up procedures.

- 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 sends
a Transaction Reply not including a ServiceChangeMgcId parameter. If
the MGC does not accept the MG's registration, it sends a Transaction
Reply, providing the address of an alternate MGC to be contacted by
including a ServiceChangeMgcId parameter.

If the MG receives a Transaction Reply that includes a
ServiceChangeMgcId parameter, it sends a ServiceChange to the MGC
specified in the ServiceChangeMgcId. It continues this process until
it gets a controlling MGC to accept its registration, or it fails to
get a reply. Upon failure to obtain a reply, either from the primary
MGC, or a designated successor, the MG tries its pre-provisioned
secondary MGCs, in order. If the MG is unable to establish a control
relationship with any MGC, it shall wait a random amount of time as
described in 9.2 and then start contacting its primary, and if
necessary, its secondary MGCs again.

It is possible that the reply to a ServiceChange with Restart will be
lost, and a command will be received by the MG prior to the receipt
of the ServiceChange response. The MG shall issue Error 505 -
Command Received before a ServiceChange Reply has been received.

11.3 Negotiation of protocol version

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

ServiceChangeReply with the lower version and thereafter all the
messages between MG and MGC shall conform to the lower version of the
protocol. If the MG is unable to comply and it has established a
transport connection to the MGC, it should close that connection. In
any event, it should reject all subsequent requests from the MGC with
error 406 - Version Not Supported.

If the MGC supports a higher version than the MG but is able to
support the lower version proposed by the MG, it shall send a
ServiceChangeReply with the lower version and thereafter all the
messages between MG and MGC shall conform to the lower version of the
protocol. If the MGC is unable to comply, it shall reject the
association, with error 406 - Version Not Supported.

Protocol version negotiation may also occur at "handoff" and
"failover" ServiceChanges.

When extending the protocol with new versions, the following rules
should be followed:

1) Existing protocol elements, i.e., procedures, parameters,
descriptor, property, values, should not be changed unless a
protocol error needs to be corrected or it becomes necessary to
change the operation of the service that is being supported by the
protocol.

2) The semantics of a command, a parameter, a descriptor, a property,
or a value should not be changed.

3) Established rules for formatting and encoding messages and
parameters should not be modified.

4) When information elements are found to be obsolete they can be
marked as not used. However, the identifier for that information
element will be marked as reserved. In that way it can not be
used in future versions.

11.4 Failure of a MG

If a MG fails, but is capable of sending a message to the MGC, it
sends a ServiceChange with an appropriate method (graceful or forced)
and specifies the Root TerminationID. When it returns to service, it
sends a ServiceChange with a "Restart" method.

Allowing the MGC to send duplicate messages to both MGs accommodates
pairs of MGs that are capable of redundant failover of one of the
MGs. Only the Working MG shall accept or reject transactions. Upon
failover, the primary MG sends a ServiceChange command with a

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

Note: Redundant failover MGs require a reliable transport, because
the protocol provides no means for a secondary MG running ALF to
acknowledge messages sent from the MGC.

11.5 Failure of an MGC

If the MG detects a failure of its controlling MGC, it attempts to
contact the next MGC on its pre-provisioned list. It starts its
attempts at the beginning (primary MGC), unless that was the MGC that
failed, in which case it starts at its first secondary MGC. It sends
a ServiceChange message with a "Failover" method and a "MGC Impending
Failure" reason. If the MG is unable to establish a control
relationship with any MGC, it shall wait a random amount of time as
described in section 9.2 and then start again contacting its primary,
and (if necessary) its secondary MGCs. When contacting its
previously controlling MGC, the MG sends the ServiceChange message
with "Disconnected" method.

In partial failure, or for manual maintenance reasons, an MGC may
wish to direct its controlled MGs to use a different MGC. To do so,
it sends a ServiceChange method to the MG with a "HandOff" method,
and its designated replacement in ServiceChangeMgcId. If "HandOff"
is supported, the MG shall send a ServiceChange message with a
"Handoff" method and a "MGC directed change" reason to the designated
MGC. If it fails to get a reply from the designated MGC, the MG
shall behave as if its MGC failed, and start contacting secondary
MGCs as specified in the previous paragraph. If the MG is unable to
establish a control relationship with any MGC, it shall wait a random
amount of time as described in 9.2 and then start contacting its
primary, and if necessary, its secondary MGCs again.

No recommendation is made on how the MGCs involved in the Handoff
maintain state information; this is considered to be out of scope of
this RFC. The MGC and MG may take the following steps when Handoff
occurs. When the MGC initiates a HandOff, the handover should be
transparent to Operations on the Media Gateway. Transactions can be
executed in any order, and could be in progress when the
ServiceChange is executed. Accordingly, commands in progress
continue and replies to all commands from the original MGC must be
sent to the transport address from which they were sent. If the
service relationship with the sending MGC has ended, the replies
should be discarded. The MG may receive outstanding transaction
replies from the new MGC. No new messages shall be sent to the new

MGC until the control association is established. Repeated
transaction requests shall be directed to the new MGC. The MG shall
maintain state on all Terminations and Contexts.

It is possible that the MGC could be implemented in such a way that a
failed MGC is replaced by a working MGC where the identity of the new
MGC is the same as the failed one. In such a case,
ServiceChangeMgcId would be specified with the previous value and the
MG shall behave as if the value was changed, and send a ServiceChange
message, as above.

Pairs of MGCs that are capable of redundant failover can notify the
controlled MGs of the failover by the above mechanism.

12 Package definition

The primary mechanism for extension is by means of Packages.
Packages define additional Properties, Events, Signals and Statistics
that may occur on Terminations.

Packages defined by IETF will appear in separate RFCs.

Packages defined by ITU-T may appear in the relevant Recommendations
(e.g., as Recommendations of the H.248 sub-series).

1) A public document or a standard forum document, which can be
referenced as the document that describes the package following
the guideline above, should be specified.

2) The document shall specify the version of the Package that it
describes.

3) The document should be available on a public web server and should
have a stable URL. The site should provide a mechanism to provide
comments and appropriate responses should be returned.

12.1 Guidelines for defining packages

Packages define Properties, Events, Signals, and Statistics.

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

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

A Package will contain the following sections:

12.1.1 Package

Overall description of the package, specifying:

Package Name: only descriptive

PackageID: is an identifier

Description:

Version:

A new version of a package can only add additional Properties,
Events, Signals, Statistics and new possible values for an
existing parameter described in the original package. No
deletions or modifications shall be allowed. A version is an
integer in the range from 1 to 99.

Designed to be extended only (Optional):

This indicates that the package has been expressly designed to
be extended by others, not to be directly referenced. For
example, the package may not have any function on its own or be
nonsensical on its own. The MG SHOULD NOT publish this
PackageID when reporting packages.

Extends (Optional): existing package Descriptor

A package may extend an existing package. The version of the
original package must be specified. When a package extends
another package it shall only add additional Properties,
Events, Signals, Statistics and new possible values for an
existing parameter described in the original package. An
extended package shall not redefine or overload an identifier
defined in the original package and packages it may have
extended (multiple levels of extension). Hence, if package B
version 1 extends package A version 1, version 2 of B will not
be able to extend the A version 2 if A version 2 defines a name
already in B version 1.

12.1.2 Properties

Properties defined by the package, specifying:

Property Name: only descriptive

PropertyID: is an identifier

Description:

Type: One of:

Boolean

String: UTF-8 string

Octet String: A number of octets. See Annex A and Annex B.3
for encoding

Integer: 4 byte signed integer

Double: 8 byte signed integer

Character: unicode UTF-8 encoding of a single letter. Could be
more than one octet.

Enumeration: one of a list of possible unique values (see 12.3)

Sub-list: a list of several values from a list. The type of
sub-list SHALL also be specified. The type shall be chosen
from the types specified in this section (with the exception of
sub-list). For example, Type: sub-list of enumeration. The
encoding of sub-lists is specified in Annexes A and B.3.

Possible values:

A package MUST specify either a specific set of values or a
description of how values are determined. A package MUST also
specify a default value or the default behaviour when the value
is omitted from its descriptor. For example, a package may
specify that procedures related to the property are suspended
when its value is omitted. A default value (but not
procedures)
may be specified as provisionable.

Defined in:

Which H.248.1 descriptor the property is defined in.

LocalControl is for stream dependent properties.
TerminationState is for stream independent properties. These
are expected to be the most common cases, but it is possible
for properties to be defined in other descriptors.

Characteristics: Read/Write or both, and (optionally), global:

Indicates whether a property is read-only, or read-write, and
if it is global. If Global is omitted, the property is not
global. If a property is declared as global, the value of the
property is shared by all Terminations realizing the package.

12.1.3 Events

Events defined by the package, specifying:

Event name: only descriptive

EventID: is an identifier

Description:

EventsDescriptor Parameters:

Parameters used by the MGC to configure the event, and found in
the EventsDescriptor. See 12.2.

ObservedEventsDescriptor Parameters:

Parameters returned to the MGC in Notify requests and in
replies to command requests from the MGC that audit
ObservedEventsDescriptor, and found in the
ObservedEventsDescriptor. See 12.2.

12.1.4 Signals

Signals defined by the package, specifying:

Signal Name: only descriptive

SignalID: is an identifier. SignalID is used in a
SignalsDescriptor

Description

SignalType: one of:

OO (On/Off)

TO (TimeOut)

BR (Brief)

NOTE - SignalType may be defined such that it is dependent on the
value of one or more parameters. The package MUST specify a
default signal type. If the default type is TO, the package MUST
specify a default duration which may be provisioned. A default
duration is meaningless for BR.

Duration: in hundredths of seconds

Additional Parameters: see 12.2

12.1.5 Statistics

Statistics defined by the package, specifying:

Statistic name: only descriptive

StatisticID: is an identifier

StatisticID is used in a StatisticsDescriptor

Description:

Units: unit of measure, e.g., milliseconds, packets

12.1.6 Procedures

Additional guidance on the use of the package.

12.2 Guidelines to defining Parameters to Events and Signals

Parameter Name: only descriptive

ParameterID: is an identifier. The textual ParameterID of parameters
to Events and Signals shall not start with "EPA" and "SPA",
respectively. The textual ParameterID shall also not be "ST",
"Stream", "SY", "SignalType", "DR", "Duration", "NC",
"NotifyCompletion", "KA", "Keepactive", "EB", "Embed", "DM" or
"DigitMap".

Type: One of:

Boolean

String: UTF-8 octet string

Octet String: A number of octets. See Annex A and Annex B.3 for
encoding

Integer: 4-octet signed integer

Double: 8-octet signed integer

Character: unicode UTF-8 encoding of a single letter. Could be
more than one octet.

Enumeration: one of a list of possible unique values (see 12.3)

Sub-list: a list of several values from a list (not supported for
statistics). The type of sub-list SHALL also be specified. The
type shall be chosen from the types specified in this section
(with the exception of sub-list). For example, Type: sub-list of
enumeration. The encoding of sub-lists is specified in Annexes A
and B.3.

Possible values:

A package MUST specify either a specific set of values or a
description of how values are determined. A package MUST also
specify a default value or the default behavior when the value is
omitted from its descriptor. For example, a package may specify
that procedures related to the parameter are suspended when it
value is omitted. A default value (but not procedures) may be
specified as provisionable.

Description:

12.3 Lists

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

12.4 Identifiers

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

Identifiers in binary encoding are 2 octets long.

Both text and binary values shall be specified for each identifier,
including identifiers used as values in enumerated types.

12.5 Package registration

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

13 IANA Considerations

13.1 Packages

The following considerations SHALL be met to register a package with
IANA:

1) A unique string name, unique serial number and version number is
registered for each package. The string name is used with text
encoding. The serial number shall be used with binary encoding.
Serial Numbers 0x8000 to 0xFFFF are reserved for private use.
Serial number 0 is reserved.

2) A contact name, email and postal addresses for that contact shall
be specified. The contact information shall be updated by the
defining organization as necessary.

3) A reference to a document that describes the package, which should
be public:

The document shall specify the version of the Package that it
describes.

If the document is public, it should be located on a public web
server and should have a stable URL. The site should provide a
mechanism to provide comments and appropriate responses should be
returned.

4) Packages registered by other than recognized standards bodies
shall have a minimum package name length of 8 characters.

5) All other package names are first come-first served if all other
conditions are met.

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

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

A.1 Coding of wildcards

The use of wildcards ALL and CHOOSE is allowed in the protocol. This
allows a MGC to partially specify Termination IDs and to let the MG
choose from the values that conform to the partial specification.
Termination IDs may encode a hierarchy of names. This hierarchy is
provisioned. For instance, a TerminationID may consist of a trunk
group, a trunk within the group and a circuit. Wildcarding must be
possible at all levels. The following paragraphs explain how this is
achieved.

The ASN.1 description uses octet strings of up to 8 octets in length
for Termination IDs. This means that Termination IDs consist of at
most 64 bits. A fully specified Termination ID may be preceded by a
sequence of wildcarding fields. A wildcarding field is one octet in
length. Bit 7 (the most significant bit) of this octet specifies
what type of wildcarding is invoked: if the bit value equals 1, then
the ALL wildcard is used; if the bit value if 0, then the CHOOSE
wildcard is used. Bit 6 of the wildcarding field specifies whether
the wildcarding pertains to one level in the hierarchical naming
scheme (bit value 0) or to the level of the hierarchy specified in
the wildcarding field plus all lower levels (bit value 1). Bits 0
through 5 of the wildcarding field specify the bit position in the
Termination ID at which the wildcarding starts.

We illustrate this scheme with some examples. In these examples, the
most significant bit in a string of bits appears on the left hand
side.

Assume that Termination IDs are three octets long and that each octet
represents a level in a hierarchical naming scheme. A valid
Termination ID is:

00000001 00011110 01010101.

Addressing ALL names with prefix 00000001 00011110 is done as
follows:

wildcarding field: 10000111

Termination ID: 00000001 00011110 xxxxxxxx.

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

Indicating to the receiver that it must choose a name with 00011110
as the second octet is done as follows:

wildcarding fields: 00010111 followed by 00000111

Termination ID: xxxxxxxx 00011110 xxxxxxxx.

The first wildcard field indicates a CHOOSE wildcard for the level in
the naming hierarchy starting at bit 23, the highest level in our
assumed naming scheme. The second wildcard field indicates a CHOOSE
wildcard for the level in the naming hierarchy starting at bit 7, the
lowest level in our assumed naming scheme.

Finally, a CHOOSE-wildcarded name with the highest level of the name
equal to 00000001 is specified as follows:

wildcard field: 01001111

Termination ID: 0000001 xxxxxxxx xxxxxxxx .

Bit value 1 at bit position 6 of the first octet of the wildcard
field indicates that the wildcarding pertains to the specified level
in the naming hierarchy and all lower levels.

Context IDs may also be wildcarded. In the case of Context IDs,
however, specifying partial names is not allowed. Context ID 0x0
SHALL be used to indicate the NULL Context, Context ID 0xFFFFFFFE
SHALL be used to indicate a CHOOSE wildcard, and Context ID
0xFFFFFFFF SHALL be used to indicate an ALL wildcard.

TerminationID 0xFFFFFFFFFFFFFFFF SHALL be used to indicate the ROOT
Termination.

A.2 ASN.1 syntax specification

This subclause contains the ASN.1 specification of the H.248.1
protocol syntax.

NOTE 1 - In case a transport mechanism is used that employs
application level framing, the definition of Transaction below
changes. Refer to the annex or to the Recommendation of the H.248
sub-series defining the transport mechanism for the definition that
applies in that case.

NOTE 2 - The ASN.1 specification below contains a clause defining
TerminationIDList as a sequence of TerminationIDs. The length of
this sequence SHALL be one, except possibly when used in
contextAuditResult.

NOTE 3 - This syntax specification does not enforce all
restrictions on element inclusions and values. Some additional
restrictions are stated in comments and other restrictions appear
in the text of this RFC. These additional restrictions
are part of the protocol even though not enforced by this
specification.

NOTE 4 - The ASN.1 module in this Annex uses octet string types to
encode values for property parameter, signal parameter and event
parameter values and statistics. The actual types of these values
vary and are specified in Annex C or the relevant package
definition.

A value is first BER-encoded based on its type using the table below.
The result of this BER-encoding is then encoded as an ASN.1 octet
string, "double wrapping" the value. The format specified in Annex C
or the package relates to BER encoding according to the following
table:

Type Specified in Package ASN.1 BER Type

String IA5String or UTF8String (Note 4)

Integer (4 Octet) INTEGER

Double (8 octet signed int) INTEGER (Note 3)

Character (UTF-8, Note 1) IA5String

Enumeration ENUMERATED

Boolean BOOLEAN

Unsigned Integer (Note 2) INTEGER (Note 3)

Octet (String) OCTET STRING

Note 1: Can be more than one byte

Note 2: Unsigned integer is referenced in Annex C

Note 3: The BER encoding of INTEGER does not imply the use of 4
bytes.

Note 4: String should be encoded as IA5String when the contents
are all ASCII characters, but as UTF8String if it contains any
Non-ASCII characters.

See ITU-T Rec. X.690, 8.7, for the definition of the encoding of an
octet string value.

MEDIA-GATEWAY-CONTROL DEFINITIONS AUTOMATIC TAGS::=
BEGIN

MegacoMessage ::= SEQUENCE
{
authHeader AuthenticationHeader OPTIONAL,
mess Message
}

AuthenticationHeader ::= SEQUENCE
{
secParmIndex SecurityParmIndex,
seqNum SequenceNum,
ad AuthData
}

SecurityParmIndex ::= OCTET STRING(SIZE(4))

SequenceNum ::= OCTET STRING(SIZE(4))

AuthData ::= OCTET STRING (SIZE (12..32))

Message ::= SEQUENCE
{
version INTEGER(0..99),
-- The version of the protocol defined here is equal to 1.
mId MId, -- Name/address of message originator
messageBody CHOICE
{
messageError ErrorDescriptor,

transactions SEQUENCE OF Transaction
},
...
}

MId ::= CHOICE
{
ip4Address IP4Address,
ip6Address IP6Address,
domainName DomainName,
deviceName PathName,
mtpAddress OCTET STRING(SIZE(2..4)),
-- Addressing structure of mtpAddress:
-- 25 - 15 0
-- PC NI
-- 24 - 14 bits 2 bits
-- Note: 14 bits are defined for international use.
-- Two national options exist where the point code is 16 or 24
-- bits.
-- To octet align the mtpAddress, the MSBs shall be encoded as 0s.
...
}

DomainName ::= SEQUENCE
{
name IA5String,
-- The name starts with an alphanumeric digit followed by a
-- sequence of alphanumeric digits, hyphens and dots. No two
-- dots shall occur consecutively.
portNumber INTEGER(0..65535) OPTIONAL
}

IP4Address ::= SEQUENCE
{
address OCTET STRING (SIZE(4)),
portNumber INTEGER(0..65535) OPTIONAL
}

IP6Address ::= SEQUENCE
{
address OCTET STRING (SIZE(16)),
portNumber INTEGER(0..65535) OPTIONAL
}

PathName ::= IA5String(SIZE (1..64))
-- See A.3

Transaction ::= CHOICE

{
transactionRequest TransactionRequest,
transactionPending TransactionPending,
transactionReply TransactionReply,
transactionResponseAck TransactionResponseAck,
-- use of response acks is dependent on underlying transport
...
}

TransactionId ::= INTEGER(0..4294967295) -- 32-bit unsigned integer

TransactionRequest ::= SEQUENCE
{
transactionId TransactionId,
actions SEQUENCE OF ActionRequest,
...
}

TransactionPending ::= SEQUENCE
{
transactionId TransactionId,
...
}

TransactionReply ::= SEQUENCE
{
transactionId TransactionId,
immAckRequired NULL OPTIONAL,
transactionResult CHOICE
{
transactionError ErrorDescriptor,
actionReplies SEQUENCE OF ActionReply
},
...
}

TransactionResponseAck ::= SEQUENCE OF TransactionAck
TransactionAck ::= SEQUENCE
{
firstAck TransactionId,
lastAck TransactionId OPTIONAL
}

ErrorDescriptor ::= SEQUENCE
{
errorCode ErrorCode,
errorText ErrorText OPTIONAL
}

ErrorCode ::= INTEGER(0..65535)
-- See clause 13 for IANA Considerations with respect to error codes

ErrorText ::= IA5String

ContextID ::= INTEGER(0..4294967295)

-- Context NULL Value: 0
-- Context CHOOSE Value: 4294967294 (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,
descriptors SEQUENCE OF AmmDescriptor,
-- At most one descriptor of each type (see AmmDescriptor)
-- allowed in the sequence.
...
}

AmmDescriptor ::= CHOICE
{
mediaDescriptor MediaDescriptor,
modemDescriptor ModemDescriptor,
muxDescriptor MuxDescriptor,
eventsDescriptor EventsDescriptor,
eventBufferDescriptor EventBufferDescriptor,
signalsDescriptor SignalsDescriptor,
digitMapDescriptor DigitMapDescriptor,
auditDescriptor AuditDescriptor,
...
}

AmmsReply ::= SEQUENCE
{
terminationID TerminationIDList,
terminationAudit TerminationAudit OPTIONAL,
...
}

SubtractRequest ::= SEQUENCE
{
terminationID TerminationIDList,
auditDescriptor AuditDescriptor OPTIONAL,
...
}

AuditRequest ::= SEQUENCE
{
terminationID TerminationID,
auditDescriptor AuditDescriptor,
...
}

AuditReply ::= CHOICE
{
contextAuditResult TerminationIDList,
error ErrorDescriptor,
auditResult AuditResult,
...
}

AuditResult ::= SEQUENCE
{

terminationID TerminationID,
terminationAuditResult TerminationAudit
}

TerminationAudit ::= SEQUENCE OF AuditReturnParameter

AuditReturnParameter ::= CHOICE
{
errorDescriptor ErrorDescriptor,
mediaDescriptor MediaDescriptor,
modemDescriptor ModemDescriptor,
muxDescriptor MuxDescriptor,
eventsDescriptor EventsDescriptor,
eventBufferDescriptor EventBufferDescriptor,
signalsDescriptor SignalsDescriptor,
digitMapDescriptor DigitMapDescriptor,
observedEventsDescriptor ObservedEventsDescriptor,
statisticsDescriptor StatisticsDescriptor,
packagesDescriptor PackagesDescriptor,
emptyDescriptors AuditDescriptor,
...
}

AuditDescriptor ::= SEQUENCE
{
auditToken BIT STRING
{
muxToken(0), modemToken(1), mediaToken(2),
eventsToken(3), signalsToken(4),
digitMapToken(5), statsToken(6),
observedEventsToken(7),
packagesToken(8), eventBufferToken(9)
} OPTIONAL,
...
}

NotifyRequest ::= SEQUENCE
{
terminationID TerminationIDList,
observedEventsDescriptor ObservedEventsDescriptor,
errorDescriptor ErrorDescriptor OPTIONAL,
...
}

NotifyReply ::= SEQUENCE
{
terminationID TerminationIDList,
errorDescriptor ErrorDescriptor OPTIONAL,
...
}

ObservedEventsDescriptor ::= SEQUENCE
{
requestId RequestID,
observedEventLst SEQUENCE OF ObservedEvent
}

ObservedEvent ::= SEQUENCE
{
eventName EventName,
streamID StreamID OPTIONAL,
eventParList SEQUENCE OF EventParameter,
timeNotation TimeNotation OPTIONAL,
...
}

EventName ::= PkgdName

EventParameter ::= SEQUENCE
{
eventParameterName Name,
value Value,
-- For use of extraInfo see the comment related to PropertyParm
extraInfo CHOICE
{
relation Relation,
range BOOLEAN,
sublist BOOLEAN
} OPTIONAL,
...
}

ServiceChangeRequest ::= SEQUENCE
{
terminationID TerminationIDList,
serviceChangeParms ServiceChangeParm,
...
}

ServiceChangeReply ::= SEQUENCE
{
terminationID TerminationIDList,

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 A.1 for explanation of wildcarding mechanism.
-- Termination ID 0xFFFFFFFFFFFFFFFF indicates the ROOT Termination.

TerminationIDList ::= SEQUENCE OF TerminationID

MediaDescriptor ::= SEQUENCE
{

termStateDescr TerminationStateDescriptor OPTIONAL,
streams CHOICE
{
oneStream StreamParms,
multiStream SEQUENCE OF StreamDescriptor
} OPTIONAL,
...
}

StreamDescriptor ::= SEQUENCE
{
streamID StreamID,
streamParms StreamParms
}

StreamParms ::= SEQUENCE
{
localControlDescriptor LocalControlDescriptor OPTIONAL,
localDescriptor LocalRemoteDescriptor OPTIONAL,

remoteDescriptor LocalRemoteDescriptor OPTIONAL,
...
}

LocalControlDescriptor ::= SEQUENCE
{

streamMode StreamMode OPTIONAL,
reserveValue BOOLEAN OPTIONAL,
reserveGroup BOOLEAN OPTIONAL,
propertyParms SEQUENCE OF PropertyParm,
...
}

StreamMode ::= ENUMERATED
{
sendOnly(0),
recvOnly(1),
sendRecv(2),
inactive(3),
loopBack(4),
...
}

-- 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
-- If the sublist field is not selected, a longer sequence means
-- "choose one of the values" (i.e., value1 OR value2 OR ...)
-- If the sublist field is selected,
-- a sequence with more than one element encodes the value of a
-- list-valued property (i.e., value1 AND value2 AND ...).
-- 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,
sublist BOOLEAN
} OPTIONAL,
...
}

Name ::= OCTET STRING(SIZE(2))

PkgdName ::= OCTET STRING(SIZE(4))
-- represents Package Name (2 octets) plus Property, Event,
-- Signal Names or Statistics ID. (2 octets)
-- To wildcard a package use 0xFFFF for first two octets, choose
-- is not allowed. To reference native property tag specified in
-- Annex C, use 0x0000 as first two octets.
-- To wildcard a Property, Event, Signal, or Statistics ID, use
-- 0xFFFF for last two octets, choose is not allowed.
-- Wildcarding of Package Name is permitted only if Property,
-- Event, Signal, or Statistics ID are
-- also wildcarded.

Relation ::= ENUMERATED
{
greaterThan(0),
smallerThan(1),
unequalTo(2),
...
}

LocalRemoteDescriptor ::= SEQUENCE
{
propGrps SEQUENCE OF PropertyGroup,
...
}

PropertyGroup ::= SEQUENCE OF PropertyParm

TerminationStateDescriptor ::= SEQUENCE
{
propertyParms SEQUENCE OF PropertyParm,
eventBufferControl EventBufferControl OPTIONAL,
serviceState ServiceState OPTIONAL,
...
}

EventBufferControl ::= ENUMERATED
{
off(0),
lockStep(1),
...
}

ServiceState ::= ENUMERATED

{
test(0),
outOfSvc(1),
inSvc(2),
...
}

MuxDescriptor ::= SEQUENCE
{
muxType MuxType,
termList SEQUENCE OF TerminationID,
nonStandardData NonStandardData OPTIONAL,
...
}

MuxType ::= ENUMERATED
{
h221(0),
h223(1),
h226(2),
v76(3),
...
}

StreamID ::= INTEGER(0..65535) -- 16-bit unsigned integer

EventsDescriptor ::= SEQUENCE
{
requestID RequestID OPTIONAL,
-- RequestID must be present if eventList
-- is non empty
eventList SEQUENCE OF RequestedEvent,
...
}

RequestedEvent ::= SEQUENCE
{
pkgdName PkgdName,

streamID StreamID OPTIONAL,
eventAction RequestedActions OPTIONAL,
evParList SEQUENCE OF EventParameter,
...
}

RequestedActions ::= SEQUENCE
{
keepActive BOOLEAN OPTIONAL,
eventDM EventDM OPTIONAL,
secondEvent SecondEventsDescriptor OPTIONAL,
signalsDescriptor SignalsDescriptor OPTIONAL,
...
}

EventDM ::= CHOICE
{ digitMapName DigitMapName,
digitMapValue DigitMapValue
}

SecondEventsDescriptor ::= SEQUENCE
{
requestID RequestID OPTIONAL,
eventList SEQUENCE OF SecondRequestedEvent,
...
}

SecondRequestedEvent ::= SEQUENCE
{
pkgdName PkgdName,
streamID StreamID OPTIONAL,
eventAction SecondRequestedActions OPTIONAL,
evParList SEQUENCE OF EventParameter,
...
}

SecondRequestedActions ::= SEQUENCE
{
keepActive BOOLEAN OPTIONAL,
eventDM EventDM OPTIONAL,
signalsDescriptor SignalsDescriptor OPTIONAL,
...
}

EventBufferDescriptor ::= SEQUENCE OF EventSpec

EventSpec ::= SEQUENCE
{

eventName EventName,
streamID StreamID OPTIONAL,
eventParList SEQUENCE OF EventParameter,
...
}

SignalsDescriptor ::= SEQUENCE OF SignalRequest

SignalRequest ::=CHOICE
{
signal Signal,
seqSigList SeqSigList,
...
}

SeqSigList ::= SEQUENCE
{
id INTEGER(0..65535),
signalList SEQUENCE OF Signal
}

Signal ::= SEQUENCE
{
signalName SignalName,
streamID StreamID OPTIONAL,
sigType SignalType OPTIONAL,
duration INTEGER (0..65535) OPTIONAL,
notifyCompletion NotifyCompletion OPTIONAL,
keepActive BOOLEAN OPTIONAL,
sigParList SEQUENCE OF SigParameter,
...
}

SignalType ::= ENUMERATED
{
brief(0),
onOff(1),
timeOut(2),
...
}

SignalName ::= PkgdName

NotifyCompletion ::= BIT STRING
{
onTimeOut(0), onInterruptByEvent(1),
onInterruptByNewSignalDescr(2), otherReason(3)
}

SigParameter ::= SEQUENCE
{
sigParameterName Name,
value Value,
-- For use of extraInfo see the comment related to PropertyParm
extraInfo CHOICE
{
relation Relation,
range BOOLEAN,
sublist BOOLEAN

} OPTIONAL,
...
}

-- For an AuditCapReply with all events, the RequestID SHALL be ALL.
-- ALL is represented by 0xffffffff.

RequestID ::= INTEGER(0..4294967295) -- 32-bit unsigned integer

ModemDescriptor ::= SEQUENCE
{
mtl SEQUENCE OF ModemType,
mpl SEQUENCE OF PropertyParm,
nonStandardData NonStandardData OPTIONAL
}

ModemType ::= ENUMERATED
{
v18(0),
v22(1),
v22bis(2),
v32(3),
v32bis(4),
v34(5),
v90(6),
v91(7),
synchISDN(8),
...
}

DigitMapDescriptor ::= SEQUENCE
{
digitMapName DigitMapName OPTIONAL,
digitMapValue DigitMapValue OPTIONAL
}

DigitMapName ::= Name

DigitMapValue ::= SEQUENCE
{
startTimer INTEGER(0..99) OPTIONAL,
shortTimer INTEGER(0..99) OPTIONAL,
longTimer INTEGER(0..99) OPTIONAL,
digitMapBody IA5String,
-- Units are seconds for start, short and long timers, and
-- hundreds of milliseconds for duration timer. Thus start,
-- short, and long range from 1 to 99 seconds and duration
-- from 100 ms to 9.9 s
-- See A.3 for explanation of digit map syntax
...
}

ServiceChangeParm ::= SEQUENCE
{
serviceChangeMethod ServiceChangeMethod,
serviceChangeAddress ServiceChangeAddress OPTIONAL,
serviceChangeVersion INTEGER(0..99) OPTIONAL,
serviceChangeProfile ServiceChangeProfile OPTIONAL,
serviceChangeReason Value,
-- A serviceChangeReason consists of a numeric reason code
-- and an optional text description.
-- The serviceChangeReason SHALL be a string consisting of
-- a decimal reason code, optionally followed by a single
-- space character and a textual description string.
-- This string is first BER-encoded as an IA5String.
-- The result of this BER-encoding is then encoded as
-- an ASN.1 OCTET STRING type, "double wrapping" the
-- value as was done for package elements.
serviceChangeDelay INTEGER(0..4294967295) OPTIONAL,
-- 32-bit unsigned integer
serviceChangeMgcId MId OPTIONAL,
timeStamp TimeNotation OPTIONAL,
nonStandardData NonStandardData OPTIONAL,
...
}

ServiceChangeAddress ::= CHOICE
{
portNumber INTEGER(0..65535), -- TCP/UDP port number
ip4Address IP4Address,
ip6Address IP6Address,
domainName DomainName,
deviceName PathName,
mtpAddress OCTET STRING(SIZE(2..4)),

...
}

ServiceChangeResParm ::= SEQUENCE
{
serviceChangeMgcId MId OPTIONAL,
serviceChangeAddress ServiceChangeAddress OPTIONAL,
serviceChangeVersion INTEGER(0..99) OPTIONAL,
serviceChangeProfile ServiceChangeProfile OPTIONAL,
timestamp TimeNotation OPTIONAL,
...
}

ServiceChangeMethod ::= ENUMERATED

{
failover(0),
forced(1),
graceful(2),
restart(3),
disconnected(4),
handOff(5),
...
}

ServiceChangeProfile ::= SEQUENCE
{
profileName IA5String(SIZE (1..67))
-- 64 characters for name, 1 for "/", 2 for version to match ABNF
}

PackagesDescriptor ::= SEQUENCE OF PackagesItem

PackagesItem ::= SEQUENCE
{
packageName Name,
packageVersion INTEGER(0..99),
...
}

StatisticsDescriptor ::= SEQUENCE OF StatisticsParameter

StatisticsParameter ::= SEQUENCE
{
statName PkgdName,
statValue Value OPTIONAL
}

NonStandardData ::= SEQUENCE
{
nonStandardIdentifier NonStandardIdentifier,
data OCTET STRING
}

NonStandardIdentifier ::= CHOICE
{
object OBJECT IDENTIFIER,
h221NonStandard H221NonStandard,
experimental IA5String(SIZE(8)),
-- first two characters should be "X-" or "X+"
...
}

H221NonStandard ::= SEQUENCE
{ t35CountryCode1 INTEGER(0..255),
t35CountryCode2 INTEGER(0..255), -- country, as per T.35
t35Extension INTEGER(0..255), -- assigned nationally
manufacturerCode INTEGER(0..65535), -- assigned nationally
...
}

TimeNotation ::= SEQUENCE
{
date IA5String(SIZE(8)), -- yyyymmdd format
time IA5String(SIZE(8)) -- hhmmssss format
-- per ISO 8601:1988
}

Value ::= SEQUENCE OF OCTET STRING

END

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 [RFC2234]. The syntax for digit maps presented in
this subclause is for illustrative purposes only. The definition of
digitMap in Annex B takes precedence in the case of differences
between the two.

digitMap = (digitString / LWSP "(" LWSP digitStringList LWSP ")"
LWSP)

digitStringList = digitString *( LWSP "" LWSP digitString )
digitString = 1*(digitStringElement)
digitStringElement = digitPosition [DOT]
digitPosition = digitMapLetter / digitMapRange
digitMapRange = ("x" / (LWSP "[" LWSP digitLetter LWSP "]" LWSP))
digitLetter = *((DIGIT "-" DIGIT) /digitMapLetter)
digitMapLetter = DIGIT ;digits 0-9
/ %x41-4B / %x61-6B ;a-k and A-K
/ "L"/ "S" ;Inter-event timers
;(long, short)
/ "Z" ;Long duration event
DOT = %x2E ; "."
LWSP = *(WSP / COMMENT / EOL)
WSP = SP / HTAB
COMMENT = ";" *(SafeChar / RestChar / WSP) EOL
EOL = (CR [LF]) / LF
SP = %x20
HTAB = %x09
CR = %x0D
LF = %x0A
SafeChar = DIGIT / ALPHA / "+" / "-" / "&" / "!" / "_" / "/" /
"'" / "?" / "@" / "^" / "`" / "~" / "*" / "$" / "" /
"(" / ")" / "%" / "."
RestChar = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#" /
"<" / ">" / "=" / %x22
DIGIT = %x30-39 ; digits 0 through 9
ALPHA = %x41-5A / %x61-7A; A-Z, a-z

A path name is also a string with syntactic restrictions imposed upon
it. The ABNF production defining it is copied from Annex B.

; Total length of pathNAME must not exceed 64 chars.
pathNAME = ["*"] NAME *("/" / "*"/ ALPHA / DIGIT /"_" / "$" )
["@" pathDomainName ]

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

ANNEX B - Text encoding of the protocol

B.1 Coding of wildcards

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

B.2 ABNF specification

The protocol syntax is presented in ABNF according to RFC2234.

Note 1 - This syntax specification does not enforce all
restrictions on element inclusions and values. Some additional
restrictions are stated in comments and other restrictions appear
in the text of this RFC. These additional restrictions are part
of the protocol even though not enforced by this specification.

Note 2 - The syntax is context-dependent. For example, "Add" can
be the AddToken or a NAME depending on the context in which it
occurs.

Everything in the ABNF and text encoding is case insensitive. This
includes TerminationIDs, digitmap Ids etc. SDP is case sensitive as
per RFC2327.

; NOTE -- The ABNF in this section uses the VALUE construct (or lists
; of VALUE constructs) to encode various package element values
; (properties, signal parameters, etc.). The types of these values
; vary and are specified the relevant package definition. Several
; such types are described in section 12.2.
;
; The ABNF specification for VALUE allows a quotedString form or a
; collection of SafeChars. The encoding of package element values
; into ABNF VALUES is specified below. If a type's encoding allows
; characters other than SafeChars, the quotedString form MUST be used
; for all values of that type, even for specific values that consist
; only of SafeChars.
;

; String: A string MUST use the quotedString form of VALUE and can
; contain anything allowable in the quotedString form.
;
; Integer, Double, and Unsigned Integer: Decimal values can be
; encoded using characters 0-9. Hexadecimal values must be prefixed
; with '0x' and can use characters 0-9,a-f,A-F. An octal format is
; not supported. Negative integers start with '-' and MUST be
; Decimal. The SafeChar form of VALUE MUST be used.
;
; Character: A UTF-8 encoding of a single letter surrounded by
; double quotes.
;
; Enumeration: An enumeration MUST use the SafeChar form of VALUE
; and can contain anything allowable in the SafeChar form.
;
; Boolean: Boolean values are encoded as "on" and "off" and are
; case insensitive. The SafeChar form of VALUE MUST be used.
;
; Future types: Any defined types MUST fit within
; the ABNF specification of VALUE. Specifically, if a type's
; encoding allows characters other than SafeChars, the quotedString
; form MUST be used for all values of that type, even for specific
; values that consist only of SafeChars.
;
; Note that there is no way to use the double quote character within
; a value.
;
; Note that SDP disallows whitespace at the beginning of a line,
; Megaco ABNF allows whitespace before the beginning of the SDP in
; the Local/Remote descriptor. Parsers should accept whitespace
; between the LBRKT following the Local/Remote token and the
; beginning of the SDP.

megacoMessage = LWSP [authenticationHeader SEP ] message

authenticationHeader = AuthToken EQUAL SecurityParmIndex COLON
SequenceNum COLON AuthData

SecurityParmIndex = "0x" 8(HEXDIG)
SequenceNum = "0x" 8(HEXDIG)
AuthData = "0x" 24*64(HEXDIG)

message = MegacopToken SLASH Version SEP mId SEP
messageBody
; The version of the protocol defined here is equal to 1.

messageBody = ( errorDescriptor / transactionList )

transactionList = 1*( transactionRequest / transactionReply /
transactionPending / transactionResponseAck )
;Use of response acks is dependent on underlying transport

transactionPending = PendingToken EQUAL TransactionID LBRKT
RBRKT

transactionResponseAck = ResponseAckToken LBRKT transactionAck
*(COMMA transactionAck) RBRKT
transactionAck = transactionID / (transactionID "-" transactionID)

transactionRequest = TransToken EQUAL TransactionID LBRKT
actionRequest *(COMMA actionRequest) RBRKT

actionRequest = CtxToken EQUAL ContextID LBRKT ((
contextRequest [COMMA commandRequestList])
/ commandRequestList) RBRKT

contextRequest = ((contextProperties [COMMA contextAudit])
/ contextAudit)

contextProperties = contextProperty *(COMMA contextProperty)

; at-most-once
contextProperty = (topologyDescriptor / priority / EmergencyToken)

contextAudit = ContextAuditToken LBRKT contextAuditProperties
*(COMMA contextAuditProperties) RBRKT

; at-most-once
contextAuditProperties = ( TopologyToken / EmergencyToken /
PriorityToken )

; "O-" indicates an optional command
; "W-" indicates a wildcarded response to a command
commandRequestList = ["O-"] ["W-"] commandRequest
*(COMMA ["O-"] ["W-"]commandRequest)

commandRequest = ( ammRequest / subtractRequest / auditRequest /
notifyRequest / serviceChangeRequest)

transactionReply = ReplyToken EQUAL TransactionID LBRKT
[ ImmAckRequiredToken COMMA]
( errorDescriptor / actionReplyList ) RBRKT

actionReplyList = actionReply *(COMMA actionReply )

actionReply = CtxToken EQUAL ContextID LBRKT
( errorDescriptor / commandReply ) /
(commandReply COMMA errorDescriptor) ) RBRKT

commandReply = (( contextProperties [COMMA commandReplyList] ) /
commandReplyList )

commandReplyList = commandReplys *(COMMA commandReplys )

commandReplys = (serviceChangeReply / auditReply / ammsReply /
notifyReply )

;Add Move and Modify have the same request parameters
ammRequest = (AddToken / MoveToken / ModifyToken ) EQUAL
TerminationID [LBRKT ammParameter *(COMMA
ammParameter) RBRKT]

;at-most-once
ammParameter = (mediaDescriptor / modemDescriptor /
muxDescriptor / eventsDescriptor /
signalsDescriptor / digitMapDescriptor /
eventBufferDescriptor / auditDescriptor)

ammsReply = (AddToken / MoveToken / ModifyToken /
SubtractToken ) EQUAL TerminationID [ LBRKT
terminationAudit RBRKT ]

subtractRequest = SubtractToken EQUAL TerminationID
[ LBRKT auditDescriptor RBRKT]

auditRequest = (AuditValueToken / AuditCapToken ) EQUAL
TerminationID LBRKT auditDescriptor RBRKT

auditReply = (AuditValueToken / AuditCapToken )
( contextTerminationAudit / auditOther)

auditOther = EQUAL TerminationID [LBRKT
terminationAudit RBRKT]

terminationAudit = auditReturnParameter *(COMMA auditReturnParameter)

contextTerminationAudit = EQUAL CtxToken ( terminationIDList /
LBRKT errorDescriptor RBRKT )

auditReturnParameter = (mediaDescriptor / modemDescriptor /
muxDescriptor / eventsDescriptor /
signalsDescriptor / digitMapDescriptor /

observedEventsDescriptor / eventBufferDescriptor /
statisticsDescriptor / packagesDescriptor /
errorDescriptor / auditItem)

auditDescriptor = AuditToken LBRKT [ auditItem
*(COMMA auditItem) ] RBRKT

notifyRequest = NotifyToken EQUAL TerminationID
LBRKT ( observedEventsDescriptor
[ COMMA errorDescriptor ] ) RBRKT

notifyReply = NotifyToken EQUAL TerminationID
[ LBRKT errorDescriptor RBRKT ]

serviceChangeRequest = ServiceChangeToken EQUAL TerminationID
LBRKT serviceChangeDescriptor RBRKT

serviceChangeReply = ServiceChangeToken EQUAL TerminationID
[LBRKT (errorDescriptor /
serviceChangeReplyDescriptor) RBRKT]

errorDescriptor = ErrorToken EQUAL ErrorCode
LBRKT [quotedString] RBRKT

ErrorCode = 1*4(DIGIT) ; could be extended

TransactionID = UINT32

mId = (( domainAddress / domainName )
[":" portNumber]) / mtpAddress / deviceName

; ABNF allows two or more consecutive "." although it is meaningless
; in a domain name.
domainName = "<" (ALPHA / DIGIT) *63(ALPHA / DIGIT / "-" /
".") ">"
deviceName = pathNAME

;The values 0x0, 0xFFFFFFFE and 0xFFFFFFFF are reserved.
ContextID = (UINT32 / "*" / "-" / "$")

domainAddress = "[" (IPv4address / IPv6address) "]"
;RFC2373 contains the definition of IP6Addresses.
IPv6address = hexpart [ ":" IPv4address ]
IPv4address = V4hex DOT V4hex DOT V4hex DOT V4hex
V4hex = 1*3(DIGIT) ; "0".."255"
; this production, while occurring in RFC2373, is not referenced
; IPv6prefix = hexpart SLASH 1*2DIGIT
hexpart = hexseq "::" [ hexseq ] / "::" [ hexseq ] / hexseq

hexseq = hex4 *( ":" hex4)
hex4 = 1*4HEXDIG

portNumber = UINT16

; Addressing structure of mtpAddress:
; 25 - 15 0
; PC NI
; 24 - 14 bits 2 bits
; Note: 14 bits are defined for international use.
; Two national options exist where the point code is 16 or 24 bits.
; To octet align the mtpAddress the MSBs shall be encoded as 0s.
; An octet shall be represented by 2 hex digits.
mtpAddress = MTPToken LBRKT 4*8 (HEXDIG) RBRKT

terminationIDList = LBRKT TerminationID *(COMMA TerminationID) RBRKT

; Total length of pathNAME must not exceed 64 chars.
pathNAME = ["*"] NAME *("/" / "*"/ ALPHA / DIGIT /"_" / "$" )
["@" pathDomainName ]

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

TerminationID = "ROOT" / pathNAME / "$" / "*"

mediaDescriptor = MediaToken LBRKT mediaParm *(COMMA mediaParm) RBRKT

; at-most one terminationStateDescriptor
; and either streamParm(s) or streamDescriptor(s) but not both
mediaParm = (streamParm / streamDescriptor /
terminationStateDescriptor)

; at-most-once per item
streamParm = ( localDescriptor / remoteDescriptor /
localControlDescriptor )

streamDescriptor = StreamToken EQUAL StreamID LBRKT streamParm
*(COMMA streamParm) RBRKT

localControlDescriptor = LocalControlToken LBRKT localParm
*(COMMA localParm) RBRKT

; at-most-once per item except for propertyParm
localParm = ( streamMode / propertyParm / reservedValueMode
/ reservedGroupMode )

reservedValueMode = ReservedValueToken EQUAL ( "ON" / "OFF" )
reservedGroupMode = ReservedGroupToken EQUAL ( "ON" / "OFF" )

streamMode = ModeToken EQUAL streamModes

streamModes = (SendonlyToken / RecvonlyToken / SendrecvToken /
InactiveToken / LoopbackToken )

propertyParm = pkgdName parmValue
parmValue = (EQUAL alternativeValue/ INEQUAL VALUE)
alternativeValue = ( VALUE
/ LSBRKT VALUE *(COMMA VALUE) RSBRKT
; sublist (i.e., A AND B AND ...)
/ LBRKT VALUE *(COMMA VALUE) RBRKT
; alternatives (i.e., A OR B OR ...)
/ LSBRKT VALUE COLON VALUE RSBRKT )
; range

INEQUAL = LWSP (">" / "<" / "#" ) LWSP
LSBRKT = LWSP "[" LWSP
RSBRKT = LWSP "]" LWSP

; Note - The octet zero is not among the permitted characters in
; octet string. As the current definition is limited to SDP, and a
; zero octet would not be a legal character in SDP, this is not a
; concern.

localDescriptor = LocalToken LBRKT octetString RBRKT

remoteDescriptor = RemoteToken LBRKT octetString RBRKT

eventBufferDescriptor= EventBufferToken [ LBRKT eventSpec
*( COMMA eventSpec) RBRKT ]

eventSpec = pkgdName [ LBRKT eventSpecParameter
*(COMMA eventSpecParameter) RBRKT ]
eventSpecParameter = (eventStream / eventOther)

eventBufferControl = BufferToken EQUAL ( "OFF" / LockStepToken )

terminationStateDescriptor = TerminationStateToken LBRKT
terminationStateParm *( COMMA terminationStateParm ) RBRKT

; at-most-once per item except for propertyParm
terminationStateParm = (propertyParm / serviceStates /
eventBufferControl )

serviceStates = ServiceStatesToken EQUAL ( TestToken /
OutOfSvcToken / InSvcToken )

muxDescriptor = MuxToken EQUAL MuxType terminationIDList

MuxType = ( H221Token / H223Token / H226Token / V76Token
/ extensionParameter )

StreamID = UINT16
pkgdName = (PackageName SLASH ItemID) ;specific item
/ (PackageName SLASH "*") ;all items in package
/ ("*" SLASH "*") ; all items supported by the MG
PackageName = NAME
ItemID = NAME

eventsDescriptor = EventsToken [ EQUAL RequestID LBRKT
requestedEvent *( COMMA requestedEvent ) RBRKT ]

requestedEvent = pkgdName [ LBRKT eventParameter
*( COMMA eventParameter ) RBRKT ]

; at-most-once each of KeepActiveToken , eventDM and eventStream
;at most one of either embedWithSig or embedNoSig but not both
;KeepActiveToken and embedWithSig must not both be present
eventParameter = ( embedWithSig / embedNoSig / KeepActiveToken
/eventDM / eventStream / eventOther )

embedWithSig = EmbedToken LBRKT signalsDescriptor
[COMMA embedFirst ] RBRKT
embedNoSig = EmbedToken LBRKT embedFirst RBRKT

; at-most-once of each
embedFirst = EventsToken [ EQUAL RequestID LBRKT
secondRequestedEvent *(COMMA secondRequestedEvent) RBRKT ]

secondRequestedEvent = pkgdName [ LBRKT secondEventParameter
*( COMMA secondEventParameter ) RBRKT ]

; at-most-once each of embedSig , KeepActiveToken, eventDM or
; eventStream
; KeepActiveToken and embedSig must not both be present
secondEventParameter = ( embedSig / KeepActiveToken / eventDM /
eventStream / eventOther )

embedSig = EmbedToken LBRKT signalsDescriptor RBRKT

eventStream = StreamToken EQUAL StreamID

eventOther = eventParameterName parmValue

eventParameterName = NAME

eventDM = DigitMapToken EQUAL(( digitMapName ) /
(LBRKT digitMapValue RBRKT ))

signalsDescriptor = SignalsToken LBRKT [ signalParm
*(COMMA signalParm)] RBRKT

signalParm = signalList / signalRequest

signalRequest = signalName [ LBRKT sigParameter
*(COMMA sigParameter) RBRKT ]

signalList = SignalListToken EQUAL signalListId LBRKT
signalListParm *(COMMA signalListParm) RBRKT

signalListId = UINT16

;exactly once signalType, at most once duration and every signal
;parameter
signalListParm = signalRequest

signalName = pkgdName
;at-most-once sigStream, at-most-once sigSignalType,
;at-most-once sigDuration, every signalParameterName at most once
sigParameter = sigStream / sigSignalType / sigDuration / sigOther
/ notifyCompletion / KeepActiveToken
sigStream = StreamToken EQUAL StreamID
sigOther = sigParameterName parmValue
sigParameterName = NAME
sigSignalType = SignalTypeToken EQUAL signalType
signalType = (OnOffToken / TimeOutToken / BriefToken)
sigDuration = DurationToken EQUAL UINT16
notifyCompletion = NotifyCompletionToken EQUAL (LBRKT
notificationReason *(COMMA notificationReason) RBRKT)

notificationReason = ( TimeOutToken / InterruptByEventToken
/ InterruptByNewSignalsDescrToken
/ OtherReasonToken )
observedEventsDescriptor = ObservedEventsToken EQUAL RequestID
LBRKT observedEvent *(COMMA observedEvent) RBRKT

;time per event, because it might be buffered
observedEvent = [ TimeStamp LWSP COLON] LWSP
pkgdName [ LBRKT observedEventParameter
*(COMMA observedEventParameter) RBRKT ]

;at-most-once eventStream, every eventParameterName at most once
observedEventParameter = eventStream / eventOther

; For an AuditCapReply with all events, the RequestID should be ALL.
RequestID = ( UINT32 / "*" )

modemDescriptor = ModemToken (( EQUAL modemType) /
(LSBRKT modemType *(COMMA modemType) RSBRKT))
[ LBRKT propertyParm *(COMMA propertyParm) RBRKT ]

; at-most-once except for extensionParameter
modemType = (V32bisToken / V22bisToken / V18Token /
V22Token / V32Token / V34Token / V90Token /
V91Token / SynchISDNToken / extensionParameter)

digitMapDescriptor = DigitMapToken EQUAL
( ( LBRKT digitMapValue RBRKT ) /
(digitMapName [ LBRKT digitMapValue RBRKT ]) )
digitMapName = NAME
digitMapValue = ["T" COLON Timer COMMA] ["S" COLON Timer COMMA]
["L" COLON Timer COMMA] digitMap
Timer = 1*2DIGIT
; Units are seconds for T, S, and L timers, and hundreds of
; milliseconds for Z timer. Thus T, S, and L range from 1 to 99
; seconds and Z from 100 ms to 9.9 s
digitMap = (digitString /
LWSP "(" LWSP digitStringList LWSP ")" LWSP)
digitStringList = digitString *( LWSP "" LWSP digitString )
digitString = 1*(digitStringElement)
digitStringElement = digitPosition [DOT]
digitPosition = digitMapLetter / digitMapRange
digitMapRange = ("x" / (LWSP "[" LWSP digitLetter LWSP "]" LWSP))
digitLetter = *((DIGIT "-" DIGIT ) / digitMapLetter)
digitMapLetter = DIGIT ;Basic event symbols
/ %x41-4B / %x61-6B ; a-k, A-K
/ "L" / "S" ;Inter-event timers (long, short)
/ "Z" ;Long duration modifier

;at-most-once, and DigitMapToken and PackagesToken are not allowed
;in AuditCapabilities command
auditItem = ( MuxToken / ModemToken / MediaToken /
SignalsToken / EventBufferToken /
DigitMapToken / StatsToken / EventsToken /
ObservedEventsToken / PackagesToken )

serviceChangeDescriptor = ServicesToken LBRKT serviceChangeParm
*(COMMA serviceChangeParm) RBRKT

; each parameter at-most-once
; at most one of either serviceChangeAddress or serviceChangeMgcId
; but not both
; serviceChangeMethod and serviceChangeReason are REQUIRED
serviceChangeParm = (serviceChangeMethod / serviceChangeReason /
serviceChangeDelay / serviceChangeAddress /
serviceChangeProfile / extension / TimeStamp /
serviceChangeMgcId / serviceChangeVersion )

serviceChangeReplyDescriptor = ServicesToken LBRKT
servChgReplyParm *(COMMA servChgReplyParm) RBRKT

; at-most-once. Version is REQUIRED on first ServiceChange response
; at most one of either serviceChangeAddress or serviceChangeMgcId
; but not both
servChgReplyParm = (serviceChangeAddress / serviceChangeMgcId /
serviceChangeProfile / serviceChangeVersion /
TimeStamp)
serviceChangeMethod = MethodToken EQUAL (FailoverToken /
ForcedToken / GracefulToken / RestartToken /
DisconnectedToken / HandOffToken /
extensionParameter)
; A serviceChangeReason consists of a numeric reason code
; and an optional text description.
; A serviceChangeReason MUST be encoded using the quotedString
; form of VALUE.
; The quotedString SHALL contain a decimal reason code,
; optionally followed by a single space character and a
; textual description string.

serviceChangeReason = ReasonToken EQUAL VALUE
serviceChangeDelay = DelayToken EQUAL UINT32
serviceChangeAddress = ServiceChangeAddressToken EQUAL ( mId /
portNumber )
serviceChangeMgcId = MgcIdToken EQUAL mId
serviceChangeProfile = ProfileToken EQUAL NAME SLASH Version
serviceChangeVersion = VersionToken EQUAL Version
extension = extensionParameter parmValue

packagesDescriptor = PackagesToken LBRKT packagesItem
*(COMMA packagesItem) RBRKT

Version = 1*2(DIGIT)
packagesItem = NAME "-" UINT16

TimeStamp = Date "T" Time ; per ISO 8601:1988
; Date = yyyymmdd
Date = 8(DIGIT)
; Time = hhmmssss
Time = 8(DIGIT)
statisticsDescriptor = StatsToken LBRKT statisticsParameter
*(COMMA statisticsParameter ) RBRKT

;at-most-once per item
statisticsParameter = pkgdName [EQUAL VALUE]

topologyDescriptor = TopologyToken LBRKT topologyTriple
*(COMMA topologyTriple) RBRKT
topologyTriple = terminationA COMMA
terminationB COMMA topologyDirection
terminationA = TerminationID
terminationB = TerminationID
topologyDirection = BothwayToken / IsolateToken / OnewayToken

priority = PriorityToken EQUAL UINT16

extensionParameter = "X" ("-" / "+") 1*6(ALPHA / DIGIT)

; octetString is used to describe SDP defined in RFC2327.
; Caution should be taken if CRLF in RFC2327 is used.
; To be safe, use EOL in this ABNF.
; Whenever "}" appears in SDP, it is escaped by "", e.g., "}"
octetString = *(nonEscapeChar)
nonEscapeChar = ( "}" / %x01-7C / %x7E-FF )
; Note - The double-quote character is not allowed in quotedString.
quotedString = DQUOTE *(SafeChar / RestChar/ WSP) DQUOTE

UINT16 = 1*5(DIGIT) ; %x0-FFFF
UINT32 = 1*10(DIGIT) ; %x0-FFFFFFFF

NAME = ALPHA *63(ALPHA / DIGIT / "_" )
VALUE = quotedString / 1*(SafeChar)
SafeChar = DIGIT / ALPHA / "+" / "-" / "&" /
"!" / "_" / "/" / "'" / "?" / "@" /
"^" / "`" / "~" / "*" / "$" / "" /
"(" / ")" / "%" / "" / "."

EQUAL = LWSP %x3D LWSP ; "="
COLON = %x3A ; ":"
LBRKT = LWSP %x7B LWSP ; "{"
RBRKT = LWSP %x7D LWSP ; "}"
COMMA = LWSP %x2C LWSP ; ","

DOT = %x2E ; "."
SLASH = %x2F ; "/"
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
DIGIT = %x30-39 ; 0-9
DQUOTE = %x22 ; " (Double Quote)
HEXDIG = ( DIGIT / "A" / "B" / "C" / "D" / "E" / "F" )
SP = %x20 ; space
HTAB = %x09 ; horizontal tab
CR = %x0D ; Carriage return
LF = %x0A ; linefeed
LWSP = *( WSP / COMMENT / EOL )
EOL = (CR [LF] / LF )
WSP = SP / HTAB ; white space
SEP = ( WSP / EOL / COMMENT) LWSP
COMMENT = ";" *(SafeChar/ RestChar / WSP / %x22) EOL
RestChar = ";" / "[" / "]" / "{" / "}" / ":" / "," / "#" /
"<" / ">" / "="

; New Tokens added to sigParameter must take the format of SPA*
; * may be of any form i.e., SPAM
; New Tokens added to eventParameter must take the form of EPA*
; * may be of any form i.e., EPAD

AddToken = ("Add" / "A")
AuditToken = ("Audit" / "AT")
AuditCapToken = ("AuditCapability" / "AC")
AuditValueToken = ("AuditValue" / "AV")
AuthToken = ("Authentication" / "AU")
BothwayToken = ("Bothway" / "BW")
BriefToken = ("Brief" / "BR")
BufferToken = ("Buffer" / "BF")
CtxToken = ("Context" / "C")
ContextAuditToken = ("ContextAudit" / "CA")
DigitMapToken = ("DigitMap" / "DM")
DisconnectedToken = ("Disconnected" / "DC")
DelayToken = ("Delay" / "DL")
DurationToken = ("Duration" / "DR")
EmbedToken = ("Embed" / "EM")
EmergencyToken = ("Emergency" / "EG")
ErrorToken = ("Error" / "ER")
EventBufferToken = ("EventBuffer" / "EB")
EventsToken = ("Events" / "E")
FailoverToken = ("Failover" / "FL")
ForcedToken = ("Forced" / "FO")
GracefulToken = ("Graceful" / "GR")
H221Token = ("H221" )
H223Token = ("H223" )
H226Token = ("H226" )

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

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

B.3 Hexadecimal octet coding

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

Octet bit pattern Hexadecimal coding
00011011 D8
11100100 27
10000011 10100010 11001000 00001001 C1451390

B.4 Hexadecimal octet sequence

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

ANNEX C - Tags for media stream properties

Parameters for Local, Remote and LocalControl descriptors are
specified as tag-value pairs if binary encoding is used for the
protocol. This annex contains the property names (PropertyID), the
tags (Property tag), type of the property (Type) and the values
(Value). Values presented in the Value field when the field contains
references shall be regarded as "information". The reference
contains the normative values. If a value field does not contain a
reference, then the values in that field can be considered as
"normative".

Tags are given as hexadecimal numbers in this annex. When setting
the value of a property, a MGC may underspecify the value according
to one of the mechanisms specified in 7.1.1.

It is optional to support the properties in this Annex or any of its
sub-sections. For example, only three properties from C.3 and only
five properties from C.8 might be implemented.

For type "enumeration" the value is represented by the value in
brackets, e.g., Send(0), Receive(1). Annex C properties with the
types "N bits" or "M Octets" should be treated as octet strings when
encoding the protocol. Properties with "N bit integer" shall be
treated as an integers. "String" shall be treated as an IA5String
when encoding the protocol.

When a type is smaller than one octet, the value shall be stored in
the low-order bits of an octet string of size 1.

C.1 General media attributes

PropertyID Property Type Value
tag

Media 1001 Enumeration Audio(0), Video(1), Data(2)

Transmission 1002 Enumeration Send(0), Receive(1),
mode Send&Receive(2)

Number of 1003 Unsigned 0-255
Channels integer

Sampling 1004 Unsigned 0-2^32
rate integer

Bitrate 1005 Integer (0..4294967295)NOTE - Units of
100 bit/s.

ACodec 1006 Octet string Audio Codec Type:
Ref.: ITU-T Q.765
Non-ITU-T codecs are defined
with the appropriate standards
organization under a defined
Organizational Identifier.

Samplepp 1007 Unsigned Maximum samples or frames per
integer packet: 0..65535

Silencesupp 1008 Boolean Silence Suppression: True/False

Encrypttype 1009 Octet string Ref.: ITU-T H.245

Encryptkey 100A Octet string Encryption key
size Ref.: ITU-T H.235
(0..65535)

Echocanc 100B Not Used. See H.248.1 E.13 for
an example of possible Echo
Control properties.

Gain 100C Unsigned Gain in dB: 0..65535
integer

Jitterbuff 100D Unsigned Jitter buffer size in ms:
integer 0..65535

PropDelay 100E Unsigned Propagation Delay: 0..65535
integer Maximum propagation delay in
milliseconds for the bearer
connection between two media
gateways. The maximum delay
will be dependent on the bearer
technology.

RTPpayload 100F Integer Payload type in RTP Profile for
Audio and Video Conferences
with Minimal Control
Ref.: RFC1890

C.2 Mux properties

PropertyID Property tag Type Value

H222 2001 Octet string H222LogicalChannelParameters
Ref.: ITU-T H.245

H223 2002 Octet string H223LogicalChannelParameters
Ref.: ITU-T H.245

V76 2003 Octet string V76LogicalChannelParameters
Ref.: ITU-T H.245

H2250 2004 Octet string H2250LogicalChannelParameters
Ref.: ITU-T H.245

C.3 General bearer properties

PropertyID Property Type Value
tag

Mediatx 3001 Enumeration Media Transport TypeTDM
Circuit(0), ATM(1), FR(2),
Ipv4(3), Ipv6(4), ...

BIR 3002 4 octets Value depends on transport
technology

NSAP 3003 1-20 octets See NSAP.
Ref.: Annex A/X.213

C.4 General ATM properties

PropertyID Property Type Value
tag

AESA 4001 20 octets ATM End System Address

VPVC 4002 4 octets: VPCI VPCI/VCI
in first two
least Ref.: ITU-T Q.2931
significant
octets, VCI in
second two
octets

SC 4003 Enumeration Service Category: CBR(0),
nrt-VBR1(1), nrt VBR2(2),
nrt-VBR3(3), rt-VBR1(4),
rt VBR2(5), rt-VBR3(6),
UBR1(7), UBR2(8), ABR(9).
Ref.: ATM Forum UNI 4.0

BCOB 4004 5-bit integer Broadband Bearer Class
Ref.: ITU-T Q.2961.2

BBTC 4005 7-bit integer Broadband Transfer Capability
Ref.: ITU-T Q.2961.1

ATC 4006 Enumeration I.371 ATM Traffic
CapabilityDBR(0), SBR1(1),
SBR2(2), SBR3(3), ABT/IT(4),
ABT/DT(5), ABR(6)
Ref.: ITU-T I.371

STC 4007 2 bits Susceptibility to clipping:
Bits
2 1
---
0 0 not susceptible to
clipping
0 1 susceptible to
clipping
Ref.: ITU-T Q.2931

UPCC 4008 2 bits User Plane Connection
configuration:
Bits
2 1
---
0 0 point-to-point
0 1 point-to-multipoint
Ref.: ITU-T Q.2931

PCR0 4009 24-bit integer Peak Cell Rate (For CLP = 0)
Ref.: ITU-T Q.2931

SCR0 400A 24-bit integer Sustainable Cell Rate (For
CLP = 0)
Ref.: ITU-T Q.2961.1

MBS0 400B 24-bit integer Maximum Burst Size (For CLP =
0)
Ref.: ITU-T Q.2961.1

PCR1 400C 24-bit integer Peak Cell Rate (For CLP = 0 +
1)
Ref.: ITU-T Q.2931

SCR1 400D 24-bit integer Sustainable Cell Rate (For
CLP = 0 + 1)
Ref.: ITU-T Q.2961.1

MBS1 400E 24-bit integer Maximum Burst Size (For CLP =
0 + 1)
Ref.: ITU-T Q.2961.1

BEI 400F Boolean Best Effort Indicator
Value 1 indicates that BEI is
to be included in the ATM
signaling; value 0 indicates
that BEI is not to be
included in the ATM
signaling.
Ref.: ATM Forum UNI 4.0

TI 4010 Boolean Tagging Indicator
Value 0 indicates that
tagging is not allowed; value
1 indicates that tagging is
requested.
Ref.: ITU-T Q.2961.1

FD 4011 Boolean Frame Discard
Value 0 indicates that no
frame discard is allowed;
value 1 indicates that frame
discard is allowed.
Ref.: ATM Forum UNI 4.0

A2PCDV 4012 24-bit integer Acceptable 2-point CDV
Ref.: ITU-T Q.2965.2

C2PCDV 4013 24-bit integer Cumulative 2-point CDV
Ref.: ITU-T Q.2965.2

APPCDV 4014 24-bit integer Acceptable P-P CDV
Ref.: ATM Forum UNI 4.0

CPPCDV 4015 24-bit integer Cumulative P-P CDV
Ref.: ATM Forum UNI 4.0

ACLR 4016 8-bit integer Acceptable Cell Loss Ratio
Ref.: ITU-T Q.2965.2, ATM
Forum UNI 4.0

MEETD 4017 16-bit integer Maximum End-to-end transit
delay
Ref.: ITU-T Q.2965.2, ATM
Forum UNI 4.0

CEETD 4018 16-bit integer Cumulative End-to-end transit
delay
Ref.: ITU-T Q.2965.2, ATM
Forum UNI 4.0

QosClass 4019 Integer 0-5 QoS Class

QoS Class Meaning

0 Default QoS
associated
with the ATC
as defined
in ITU-T
Q.2961.2

1 Stringent

2 Tolerant

3 Bi-level

4 Unbounded

5 Stringent
Bi-level
Ref.: ITU-T Q.2965.1

AALtype 401A 1 octet AAL Type
Bits
8 7 6 5 4 3 2 1
---------------
0 0 0 0 0 0 0 0 AAL for
voice
0 0 0 0 0 0 0 1 AAL type 1
0 0 0 0 0 0 1 0 AAL type 2
0 0 0 0 0 0 1 1 AAL type
3/4
0 0 0 0 0 1 0 1 AAL type 5

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

C.5 Frame Relay

PropertyID Property Type Value
tag

DLCI 5001 Unsigned Data link connection
integer id

CID 5002 Unsigned sub-channel id
integer

SID/Noiselevel 5003 Unsigned silence insertion
integer descriptor

Primary Payload 5004 Unsigned Primary Payload Type
type integer Covers FAX and codecs

C.6 IP

PropertyID Property tag Type Value

IPv4 6001 32 bits Ipv4Address Ipv4Address
Ref.: IETF RFC791

IPv6 6002 128 bits IPv6 Address
Ref.: 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
the referenced
Recommendation.
ESEANSEA
Ref.: ITU-T Q.2630.1

BIR See C.3 4 octets Served user generated
reference as defined in
the referenced
Recommendation.
SUGR
Ref.: ITU-T Q.2630.1

ALC 7002 12 octets AAL2 link
characteristics as
defined in the
referenced
Recommendation.
Maximum/Average CPS-SDU
bit rate;
Maximum/Average CPS-SDU
size
Ref.: ITU-T Q.2630.1

SSCS 7003 I.366.2: Audio (8 Service specific
octets); Multirate (3 convergence sublayer
octets), or I.366.1: information as defined
SAR-assured (14 in:
octets);SAR-unassured - ITU-T Q.2630.1,and
(7 octets). used in:
- ITU-T I.366.2:
Audio/Multirate;
- ITU-T I.366.1: SAR-
assured/unassured.
Ref.: ITU-T Q.2630.1,
I.366.1 and I.366.2

SUT 7004 1..254 octets Served user transport
parameter as defined in
the referenced
Recommendation.
Ref.: ITU-T Q.2630.1

TCI 7005 Boolean Test connection
indicator as defined in
the referenced
Recommendation.
Ref.: ITU-T Q.2630.1

Timer_CU 7006 32-bit integer Timer-CU
Milliseconds to hold
partially filled cell
before sending.

MaxCPSSDU 7007 8-bit integer Maximum Common Part
Sublayer Service Data
Unit
Ref.: ITU-T Q.2630.1

CID 7008 8 bits subchannel id: 0-255
Ref.: ITU-T I.363.2
C.8 ATM AAL1

PropertyID Property Type Value
tag

BIR See table 4-29 octets GIT (Generic Identifier
in C.3 Transport)
Ref.: ITU-T Q.2941.1

AAL1ST 8001 1 octet AAL1 Subtype
Bits
8 7 6 5 4 3 2 1
---------------
0 0 0 0 0 0 0 0 null
0 0 0 0 0 0 0 1 voiceband
signal transport on 64 kbit/s
0 0 0 0 0 0 1 0 circuit
transport
0 0 0 0 0 1 0 0 high-quality
audio signal transport
0 0 0 0 0 1 0 1 video signal
transport
Ref.: ITU-T Q.2931

CBRR 8002 1 octet CBR Rate
Bits
8 7 6 5 4 3 2 1
---------------
0 0 0 0 0 0 0 1 64 kbit/s
0 0 0 0 0 1 0 0 1544 kbit/s
0 0 0 0 0 1 0 1 6312 kbit/s
0 0 0 0 0 1 1 0 32 064 kbit/s
0 0 0 0 0 1 1 1 44 736 kbit/s
0 0 0 0 1 0 0 0 97 728 kbit/s
0 0 0 1 0 0 0 0 2048 kbit/s
0 0 0 1 0 0 0 1 8448 kbit/s
0 0 0 1 0 0 1 0 34 368 kbit/s
0 0 0 1 0 0 1 1 139 264 kbit/s
0 1 0 0 0 0 0 0 n x 64 kbit/s
0 1 0 0 0 0 0 1 n x 8 kbit/s
Ref.: ITU-T Q.2931

MULT See table Multiplier, or n x 64k/8k/300
in C.9 Ref.: ITU-T Q.2931

SCRI 8003 1 octet Source Clock Frequency Recovery
Method
Bits
8 7 6 5 4 3 2 1
---------------
0 0 0 0 0 0 0 0 null
0 0 0 0 0 0 0 1 SRTS
0 0 0 0 0 0 1 0 ACM
Ref.: ITU-T Q.2931

ECM 8004 1 octet Error Correction Method
Bits
8 7 6 5 4 3 2 1
---------------
0 0 0 0 0 0 0 0 null
0 0 0 0 0 0 0 1 FEC - Loss
0 0 0 0 0 0 1 0 FEC - Delay
Ref.: ITU-T Q.2931

SDTB 8005 16-bit Structured Data Transfer
integer Blocksize
Block size of SDT CBR service
Ref.: ITU-T I.363.1

PFCI 8006 8-bit Partially filled cells identifier
integer 1-47
Ref.: ITU-T I.363.1

C.9 Bearer capabilities

The table entries referencing Recommendation Q.931 refer to the
encoding in the bearer capability information element of Q.931, not
to the low layer information element.

PropertyID Tag Type Value

TMR 9001 1 octet Transmission Medium
Requirement (Q.763)
Bits
87654321
--------
00000000 speech
00000001 spare
00000010 64 kbit/s
unrestricted

00000011 3.1 kHz audio
00000100 reserved for
alternate speech (service
2)/64 kbit/s unrestricted
(service 1)
00000101 reserved for
alternate 64 kbit/s
unrestricted (service
1)/speech (service 2)
00000110 64 kbit/s preferred

The assigned codepoints
listed below are all for
unrestricted service.
00000111 2 x 64 kbit/s
00001000 384 kbit/s
00001001 1536 kbit/s
00001010 1920 kbit/s
00001011
through
00001111 spare
00010000
through
00101010:
3 x 64 kbit/s through
29 x 64 kbit/s
except
00010011 spare
00100101 spare

00101011
through
11111111 spare
Ref.: ITU-T Q.763

TMRSR 9002 1 octet Transmission Medium
Requirement Subrate
0 unspecified
1 8 kbit/s
2 16 kbit/s
3 32 kbit/s

Contcheck 9003 Boolean Continuity Check
0 continuity check not
required on this circuit
1 continuity check
required on this circuit
Ref.: ITU-T Q.763

ITC 9004 5 bits Information Transfer
Capability
Bits
5 4 3 2 1
---------
0 0 0 0 0 Speech
0 1 0 0 0 Unrestricted
digital information
0 1 0 0 1 Restricted
digital information
1 0 0 0 0 3.1 kHz audio
1 0 0 0 1 Unrestricted
digital information with
tones/announcements
1 1 0 0 0 Video
All other values are
reserved.
Ref.: ITU-T Q.763

TransMode 9005 2 bits Transfer Mode
Bits
2 1
---
0 0 Circuit mode
1 0 Packet mode
Ref.: ITU-T Q.931

TransRate 9006 5 bits Transfer Rate
Bits
5 4 3 2 1
---------
0 0 0 0 0 This code shall
be used for packet mode calls
1 0 0 0 0 64 kbit/s
1 0 0 0 1 2 x 64 kbit/s
1 0 0 1 1 384 kbit/s
1 0 1 0 1 1536 kbit/s
1 0 1 1 1 1920 kbit/s
1 1 0 0 0 Multirate (64
kbit/s base rate)
Ref.: ITU-T Q.931

MULT 9007 7 bits Rate Multiplier
Any value from 2 to n
(maximum number of B-
channels)
Ref.: ITU-T Q.931

layer1prot 9008 5 bits User Information Layer 1
Protocol
Bits
5 4 3 2 1
---------
0 0 0 0 1 ITU-T
standardized rate adaption
V.110 and X.30.
0 0 0 1 0 Recommendation
G.711 m-law
0 0 0 1 1 Recommendation
G.711 A-law
0 0 1 0 0 Recommendation
G.721 32 kbit/s ADPCM and
Recommendation I.460
0 0 1 0 1 Recommendations
H.221 and H.242
0 0 1 1 0 Recommendations
H.223 and H.245
0 0 1 1 1 Non-ITU-T
standardized rate adaption.
0 1 0 0 0 ITU-T
standardized rate adaption
V.120.
0 1 0 0 1 ITU-T
standardized rate adaption
X.31 HDLC flag stuffing
All other values are
reserved.
Ref.: ITU Recommendation
Q.931

syncasync 9009 Boolean Synchronous/Asynchronous
0 Synchronous data
1 Asynchronous data
Ref.: ITU-T Q.931

negotiation 900A Boolean Negotiation
0 In-band negotiation
possible
1 In-band negotiation not
possible
Ref.: ITU-T Q.931

Userrate 900B 5 bits User Rate
Bits
5 4 3 2 1

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

1 1 0 0 0 1.2/0.075
kbit/s Recommendations V.6
and X.1
1 1 0 0 1 0.050 kbit/s
Recommendations V.6 and X.1
1 1 0 1 0 0.075 kbit/s
Recommendations V.6 and X.1
1 1 0 1 1 0.110 kbit/s
Recommendations V.6 and X.1
1 1 1 0 0 0.150 kbit/s
Recommendations V.6 and X.1
1 1 1 0 1 0.200 kbit/s
Recommendations V.6 and X.1
1 1 1 1 0 0.300 kbit/s
Recommendations V.6 and X.1
1 1 1 1 1 12 kbit/s
Recommendation V.6
All other values are
reserved.
Ref.: ITU-T Q.931
INTRATE 900C 2 bits Intermediate Rate
Bits
2 1
---
0 0 Not used
0 1 8 kbit/s
1 0 16 kbit/s
1 1 32 kbit/s
Ref.: ITU-T Q.931

nictx 900D Boolean Network Independent Clock
(NIC) on transmission
0 Not required to send
data with network independent
clock
1 Required to send data
with network independent
clock
Ref.: ITU-T Q.931

nicrx 900E Boolean Network independent clock
(NIC) on reception
0 Cannot accept data with
network independent clock
(i.e., sender does not support
this optional procedure)
1 Can accept data with
network independent clock

(i.e., sender does support
this optional procedure)
Ref.: ITU-T Q.931

flowconttx 900F Boolean Flow Control on transmission
(Tx)
0 Not required to send
data with flow control
mechanism
1 Required to send data
with flow control mechanism
Ref.: ITU-T Q.931

flowcontrx 9010 Boolean Flow control on reception
(Rx)
0 Cannot accept data with
flow control mechanism (i.e.,
sender does not support this
optional procedure)
1 Can accept data with
flow control mechanism (i.e.,
sender does support this
optional procedure)
Ref.: ITU-T Q.931

rateadapthdr 9011 Boolean Rate adaption header/no
header
0 Rate adaption header
not included
1 Rate adaption header
included
Ref.: ITU-T Q.931

multiframe 9012 Boolean Multiple frame establishment
support in data link
0 Multiple frame
establishment not supported.
Only UI frames allowed
1 Multiple frame
establishment supported
Ref.: ITU-T Q.931

OPMODE 9013 Boolean Mode of operation
0 Bit transparent mode of
operation
1 Protocol sensitive mode
of operation
Ref.: ITU-T Q.931

llidnegot 9014 Boolean Logical link identifier
negotiation
0 Default, LLI = 256 only
1 Full protocol
negotiation
Ref.: ITU-T Q.931

assign 9015 Boolean Assignor/assignee
0 Message originator is
"default assignee"
1 Message originator is
"assignor only"
Ref.: ITU-T Q.931

inbandneg 9016 Boolean In-band/out-band negotiation
0 Negotiation is done
with USER INFORMATION
messages on a temporary
signalling connection
1 Negotiation is done in-
band using logical link zero
Ref.: ITU-T Q.931

stopbits 9017 2 bits Number of stop bits
Bits
2 1
---
0 0 Not used
0 1 1 bit
1 0 1.5 bits
1 1 2 bits
Ref.: ITU-T Q.931

databits 9018 2 bits Number of data bits excluding
parity bit if present
Bits
2 1
---
0 0 Not used
0 1 5 bits
1 0 7 bits
1 1 8 bits
Ref.: ITU-T Q.931

parity 9019 3 bits Parity information
Bits
3 2 1

------
0 0 0 Odd
0 1 0 Even
0 1 1 None
1 0 0 Forced to 0
1 0 1 Forced to 1
All other values are
reserved.
Ref.: ITU-T Q.931

duplexmode 901A Boolean Mode duplex
0 Half duplex
1 Full duplex
Ref.: ITU-T Q.931

modem 901B 6 bits Modem Type
Bits
6 5 4 3 2 1
-----------
0 0 0 0 0 0 through
0 0 0 1 0 1 National use
0 1 0 0 0 1 Rec. V.21
0 1 0 0 1 0 Rec. V.22
0 1 0 0 1 1 Rec. V.22 bis
0 1 0 1 0 0 Rec. V.23
0 1 0 1 0 1 Rec. V.26
0 1 1 0 0 1 Rec. V.26 bis
0 1 0 1 1 1 Rec. V.26 ter
0 1 1 0 0 0 Rec. V.27
0 1 1 0 0 1 Rec. V.27 bis
0 1 1 0 1 0 Rec. V.27 ter
0 1 1 0 1 1 Rec. V.29
0 1 1 1 0 1 Rec. V.32
0 1 1 1 1 0 Rec. V.34
1 0 0 0 0 0 through
1 0 1 1 1 1 National use
1 1 0 0 0 0 through
1 1 1 1 1 1 User specified
Ref.: ITU-T Q.931

layer2prot 901C 5 bits User information layer 2
protocol
Bits
5 4 3 2 1
---------
0 0 0 1 0 Rec. Q.921/I.441
0 0 1 1 0 Rec. X.25, link
layer

0 1 1 0 0 LAN logical link
control (ISO/IEC 8802 2)
All other values are
reserved.
Ref.: ITU-T Q.931

layer3prot 901D 5 bits User information layer 3
protocol
Bits
5 4 3 2 1
---------
0 0 0 1 0 ITU-T Q.931
0 0 1 1 0 ITU-T X.25,
packet layer
0 1 0 1 1 ISO/IEC TR 9577
(Protocol identification in
the network layer)
All other values are
reserved.
Ref.: ITU-T Q.931

addlayer3prot 901E Octet Additional User Information
layer 3 protocol
Bits Bits
4 3 2 1 4 3 2 1
------- -------
1 1 0 0 1 1 0 0
Internet Protocol (RFC791)
(ISO/IEC TR 9577)
1 1 0 0 1 1 1 1
Point-to-point Protocol (RFC
1661)
Ref.: ITU-T Q.931

DialledN 901F 30 Dialled Number
octets

DiallingN 9020 30 Dialling Number
octets

ECHOCI 9021 Not Used. See H.248.1 E.13
for an example of possible
Echo Control properties.

NCI 9022 1 octet Nature of Connection
Indicators
Bits
2 1 Satellite Indicator

---
0 0 no satellite circuit
in the connection
0 1 one satellite circuit
in the connection
1 0 two satellite
circuits in the connection
1 1 spare

Bits
4 3 Continuity check
--- indicator
0 0 continuity check not
required
0 1 continuity check
required on this circuit
1 0 continuity check
performed on a previous
circuit
1 1 spare

Bit
5 Echo control device
- indicator
0 outgoing echo control
device not included
1 outgoing echo control
device included

Bits
8 7 6 Spare
Ref.: ITU-T Q.763

USI 9023 Octet User Service Information
string Ref.: ITU-T Q.763 Clause 3.57

C.10 AAL5 properties

PropertyID Property Type Value
tag

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

BMSDU A002 32-bit Backwards Maximum CPCS-SDU Size:
integer Maximum CPCS-SDU size sent in the
direction from the called user to
the calling user.
Ref.: ITU-T Q.2931

SSCS See table See table See table in C.7
in C.7 in C.7 Additional values:
VPI/VCI

C.11 SDP equivalents

PropertyID Property Type Value
tag

SDP_V B001 String Protocol Version
Ref.: RFC2327

SDP_O B002 String Owner/creator and session ID
Ref.: RFC2327

SDP_S B003 String Session name
Ref.: RFC2327

SDP_I B004 String Session identifier
Ref.: RFC2327

SDP_U B005 String URI of descriptor
Ref.: RFC2327

SDC_E B006 String email address
Ref.: RFC2327

SDP_P B007 String phone number
Ref.: RFC2327

SDP_C B008 String Connection information
Ref.: RFC2327

SDP_B B009 String Bandwidth Information
Ref.: RFC2327

SDP_Z B00A String Time zone adjustment
Ref.: RFC2327

SDP_K B00B String Encryption Key
Ref.: RFC2327

SDP_A B00C String Zero or more session attributes
Ref.: RFC2327

SDP_T B00D String Active Session Time
Ref.: RFC2327

SDP_R B00E String Zero or more repeat times
Reference: RFC2327

SDP_M B00F String Media type, port, transport and format
Ref.: RFC2327

C.12 H.245

PropertyID Property Type Value
tag

OLC C001 Octet The value of H.245
OpenLogicalChannel structure.
string Ref.: ITU-T H.245

OLCack C002 Octet The value of H.245
string OpenLogicalChannelAck structure.
Ref.: ITU-T H.245

OLCcnf C003 Octet The value of H.245
string OpenLogicalChannelConfirm structure.
Ref.: ITU-T H.245

OLCrej C004 Octet The value of H.245
string OpenLogicalChannelReject structure.
Ref.: ITU-T H.245

CLC C005 Octet The value of H.245
string CloseLogicalChannel structure.
Ref.: ITU-T H.245

CLCack C006 Octet The value of H.245
string CloseLogicalChannelAck structure.
Ref.: ITU-T H.245

ANNEX D - Transport over IP

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

Protocol messages defined in this RFCmay be transmitted over UDP.
When no port is provided by the peer (see 7.2.8), commands should be
sent to the default port number: 2944 for text-encoded operation, or
2945 for binary-encoded operation. Responses must be sent to the
address and port from which the corresponding commands were sent.

ALF is a set of techniques that allows an application, as opposed to
a stack, to affect how messages are sent to the other side. A
typical ALF technique is to allow an application to change the order
of messages sent when there is a queue after it has queued them.
There is no formal specification for ALF. The procedures in Annex
D.1 contain a minimum suggested set of ALF behaviours

Implementors using IP/UDP with ALF should be aware of the
restrictions of the MTU on the maximum message size.

D.1.1 Providing At-Most-Once functionality

Messages, being carried over UDP, may be subject to losses. In the
absence of a timely response, commands are repeated. Most commands
are not idempotent. The state of the MG would become unpredictable
if, for example, Add commands were executed several times. The
transmission procedures shall thus provide an "At-Most-Once"
functionality.

Peer protocol entities are expected to keep in memory a list of the
responses that they sent to recent transactions and a list of the
transactions that are currently outstanding. The transaction
identifier of each incoming message is compared to the transaction
identifiers of the recent responses sent to the same MId. If a match
is found, the entity does not execute the transaction, but simply
repeats the response. If no match is found, the message will be
compared to the list of currently outstanding transactions. If a
match is found in that list, indicating a duplicate transaction, the
entity does not execute the transaction (see D.1.4 for procedures on
sending TransactionPending).

The procedure uses a long timer value, noted LONG-TIMER in the
following. The timer should be set larger than the maximum duration
of a transaction, which should take into account the maximum number

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" received for LONG-TIMER
seconds.

In the binary encoding, if only the firstAck is present in a response
acknowledgement (see A.2), only one transaction is acknowledged. If
both firstAck and lastAck are present, then the range of transactions
from firstAck to lastAck is acknowledged. In the text encoding, a
horizontal dash is used to indicate a range of transactions being
acknowledged (see B.2).

D.1.3 Computing retransmission timers

It is the responsibility of the requesting entity to provide suitable
timeouts for all outstanding transactions, and to retry transactions
when timeouts have been exceeded. Furthermore, when repeated
transactions fail to be acknowledged, it is the responsibility of the
requesting entity to seek redundant services and/or clear existing or
pending connections.

The specification purposely avoids specifying any value for the
retransmission timers. These values are typically network dependent.
The retransmission timers should normally estimate the timer value by
measuring the time spent between the sending of a command and the
return of a response. Implementations SHALL ensure that the
algorithm used to calculate retransmission timing performs an
exponentially increasing bacKOFf of the retransmission timeout for
each retransmission or repetition after the first one.

NOTE - One possibility is to use the algorithm implemented in
TCP-IP, which uses two variables:

- 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
RFC, in order to guarantee that no repeated packet
would be received by the gateways after LONG-TIMER seconds. A
suggested maximum value is 4 seconds.

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". They SHOULD send
this response if they receive a repetition of a transaction that is
still being executed.

Entities that receive a Transaction Pending shall switch to a
different repetition timer for repeating requests. The root
Termination has a property (ProvisionalResponseTimerValue), which can
be set to the requested maximum number of milliseconds between
receipt of a command and transmission of the TransactionPending
response. Upon receipt of a final response following receipt of
provisional responses, an immediate confirmation shall be sent, and
normal repetition timers shall be used thereafter. An entity that
sends a provisional response, SHALL include the immAckRequired field
in the ensuing final response, indicating that an immediate
confirmation is expected. Receipt of a Transaction Pending after
receipt of a reply shall be ignored.

D.1.5 Repeating Requests, Responses and Acknowledgements

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

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 becomes
unavailable.

The entities should be able to derive from the past history an
estimate of the packet loss rate due to transmission errors. In a
properly configured system, this loss rate should be kept very low,
typically less than 1%. If a Media Gateway Controller or a Media
Gateway has to repeat a message more than a few times, it is very
legitimate to assume that something else than a transmission error is
occurring. For example, given a loss rate of 1%, the probability
that five consecutive transmission attempts fail is 1 in 100 billion,
an event that should occur less than once every 10 days for a Media
Gateway Controller that processes 1000 transactions per second.
(Indeed, the number of repetition that is considered excessive should
be a function of the prevailing packet loss rate.) We should note
that the "suspicion threshold", which we will call "Max1", is
normally lower than the "disconnection threshold", which should be
set to a larger value.

A classic retransmission algorithm would simply count the number of
successive repetitions, and conclude that the association is broken
after retransmitting the packet an excessive number of times
(typically between 7 and 11 times.) In order to account for the
possibility of an undetected or in progress "failover", we modify
the classic algorithm so that if the Media Gateway receives a valid
ServiceChange message announcing a failover, it will start
transmitting outstanding commands to that new MGC. Responses to
commands are still transmitted to the source address of the command.

In order to automatically adapt to network load, this RFCspecifies
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 as described
in section 11.5. If the MG retries to connect to the current MGC it
shall use a ServiceChange with ServiceChangeMethod set to
Disconnected so that the new MGC will be aware that the MG lost one
or more transactions. The value T-MAX is related to the LONG-TIMER
value: the LONG-TIMER value is obtained by adding to T MAX the
maximum propagation delay in the network.

D.2 Using TCP

Protocol messages as defined in this RFCmay be transmitted over TCP.
When no port is specified by the other side (see 7.2.8), the commands
should be sent to the default port. The defined protocol has
messages as the unit of transfer, while TCP is a stream-oriented
protocol. TPKT, according to 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 D.1.1.

D.2.2 Transaction identifiers and three-way handshake

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

D.2.3 Computing retransmission timers

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

D.2.4 Provisional responses

As with UDP, executing some transactions may require a long time.
Entities that can predict that a transaction will require a long
execution time may send a provisional response, "Transaction
Pending". They should send this response if they receive a
repetition of a transaction that is still being executed.

Entities that receive a Transaction Pending shall switch to a longer
repetition timer for that transaction.

Entities shall retain Transactions and replies until they are
confirmed. The basic procedure of D.1.4 should be followed, but
simple timer values should be sufficient. There is no need to send
an immediate confirmation upon receipt of a final response.

D.2.5 Ordering of commands

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

ANNEX E - Basic packages

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

E.1 Generic

PackageID: g (0x0001)
Version: 1
Extends: None

Description:
Generic package for commonly encountered items.

E.1.1 Properties

None.

E.1.2 Events

Cause

EventID: cause (0x0001)
Generic error event

EventsDescriptor parameters: None

ObservedEvents Descriptor Parameters:

General Cause
ParameterID: Generalcause (0x0001)

This parameter groups the failures into six groups, which
the MGC may act upon.

Type: enumeration

Possible values:
"NR" Normal Release (0x0001)
"UR" Unavailable Resources (0x0002)
"FT" Failure, Temporary (0x0003)
"FP" Failure, Permanent (0x0004)
"IW" Interworking Error (0x0005)
"UN" Unsupported (0x0006)

Failure Cause
ParameterID: Failurecause (0x0002)

Possible values: OCTET STRING

Description: The Failure Cause is the value generated by the
Released equipment, i.e., a released network connection.
The concerned value is defined in the appropriate bearer
control protocol.

Signal Completion

EventID: sc (0x0002)

Indicates the termination of a signal for which the
notifyCompletion parameter was set to enable reporting of a
completion event. For further procedural description, see 7.1.1,
7.1.17 and 7.2.7.

EventsDescriptor parameters: None

ObservedEvents Descriptor parameters:

Signal Identity
ParameterID: SigID (0x0001)

This parameter identifies the signal which has terminated.
For a signal that is contained in a signal list, the signal
list identity parameter should also be returned indicating
the appropriate list.

Type: Binary: octet (string), Text: string

Possible values: a signal which has terminated. A signal
shall be identified using the pkgdName syntax without
wildcarding.

Termination Method
ParameterID: Meth (0x0002)

Indicates the means by which the signal terminated.

Type: enumeration

Possible values:
"TO" (0x0001) Signal timed out or otherwise completed on
its own
"EV" (0x0002) Interrupted by event
"SD" (0x0003) Halted by new Signals descriptor
"NC" (0x0004) Not completed, other cause

Signal List ID
ParameterID: SLID (0x0003)

Indicates to which signal list a signal belongs. The
SignalList ID is only returned in cases where the signal
resides in a signal list.

Type: integer

Possible values: any integer

E.1.3 Signals

None.

E.1.4 Statistics

None.

E.2 Base Root Package

PackageID: root (0x0002)
Version: 1
Extends: None

Description:
This package defines Gateway wide properties.

E.2.1 Properties

MaxNrOfContexts
PropertyID: maxNumberOfContexts (0x0001)

The value of this property gives the maximum number of contexts
that can exist at any time. The NULL context is not included in
this number.

Type: double

Possible values: 1 and up

Defined in: TerminationState

Characteristics: read only

MaxTerminationsPerContext
PropertyID: maxTerminationsPerContext (0x0002)

The maximum number of allowed terminations in a context, see 6.1

Type: integer

Possible values: any integer

Defined in: TerminationState

Characteristics: read only

normalMGExecutionTime
PropertyId: normalMGExecutionTime (0x0003)

Settable by the MGC to indicate the interval within which the MGC
expects a response to any transaction from the MG (exclusive of
network delay)

Type: integer

Possible values: any integer, represents milliseconds

Defined in: TerminationState

Characteristics: read / write

normalMGCExecutionTime
PropertyId: normalMGCExecutionTime (0x0004)

Settable by the MGC to indicate the interval within which the MG
should expects a response to any transaction from the MGC
(exclusive of network delay)

Type: integer

Possible values: any integer, represents milliseconds

Defined in: TerminationState

Characteristics: read / write

MGProvisionalResponseTimerValue
PropertyId: MGProvisionalResponseTimerValue (0x0005)

Indicates the time within which the MGC should expect a Pending
Response from the MG if a Transaction cannot be completed.

Initially set to normalMGExecutionTime plus network delay, but may
be lowered.

Type: Integer

Possible Values: any integer, represents milliseconds

Defined in: TerminationState

Characteristics: read / write

MGCProvisionalResponseTimerValue
PropertyId: MGCProvisionalResponseTimerValue (0x0006)

Indicates the time within which the MG should expect a Pending
Response from the MGC if a Transaction cannot be completed.
Initially set to normalMGCExecutionTime plus network delay, but
may be lowered.

Type: Integer

Possible Values: any integer, represents milliseconds

Defined in: TerminationState

Characteristics: read / write

E.2.2 Events

None.

E.2.3 Signals

None.

E.2.4 Statistics

None.

E.2.5 Procedures

None.

E.3 Tone Generator Package

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

Description:

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

Designed to be extended only.

E.3.1 Properties

None.

E.3.2 Events

None.

E.3.3 Signals

Play tone
SignalID: pt (0x0001)

Plays audio tone over an audio channel

Signal Type: Brief

Duration: Provisioned

Additional parameters:

Tone id list
ParameterID: tl (0x0001)

Type: list of tone ids

List of tones to be played in sequence. The list SHALL
contain one or more tone ids.

Inter signal duration
ParameterID: ind (0x0002)

Type: integer

Timeout between two consecutive tones in milliseconds

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

E.3.4 Statistics

None.

E.3.5 Procedures

None.

E.4 Tone Detection Package

PackageID: tonedet (0x0004)
Version: 1
Extends: None

This Package defines events for audio tone detection. Tones are
selected by name (tone id). MGs are expected to be provisioned with
the characteristics of appropriate tones for the country in which the
MG is located.

Designed to be extended only:
This package does not specify parameter values. It is intended to
be extendable.

E.4.1 Properties

None.

E.4.2 Events

Start tone detected
EventID: std, 0x0001

Detects the start of a tone. The characteristics of positive tone
detection are implementation dependent.

EventsDescriptor parameters:

Tone id list
ParameterID: tl (0x0001)

Type: list of tone ids

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)

Type: Enumeration

Possible values: No possible values are specified in this
package. Extensions to this package would add possible
values for tone id.

E.4.3 Signals

None.

E.4.4 Statistics

None.

E.4.5 Procedures

None.

E.5 Basic DTMF Generator Package

PackageID: dg (0x0005)
Version: 1
Extends: tonegen version 1

This package defines the basic DTMF tones as signals and extends the
allowed values of parameter tl of playtone in tonegen.

E.5.1 Properties

None.

E.5.2 Events

None.

E.5.3 Signals

DTMF character 0
SignalID: d0 (0x0010)

Generate DTMF 0 tone. The physical characteristic of DTMF 0 is
defined in the gateway.

Signal Type: Brief

Duration: Provisioned

Additional parameters:

None.

Additional values:

d0 (0x0010) is defined as a tone id for playtone

The other DTMF characters are specified in exactly the same way. A
table with all signal names and signal IDs is included. Note that
each DTMF character is defined as both a signal and a tone id, thus
extending the basic tone generation package. Also note that DTMF
SignalIds are different from the names used in a digit map.

Signal name Signal ID/Tone id

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

E.5.4 Statistics

None.

E.5.5 Procedures

None.

E.6 DTMF detection Package

PackageID: dd (0x0006)
Version: 1
Extends: tonedet version 1

This package defines the basic DTMF tones detection. This Package
extends the possible values of tone id in the "start tone detected"
"end tone detected" and "long tone detected" events.

Additional tone id values are all tone ids described in package dg
(basic DTMF generator package).

The following table maps DTMF events to digit map symbols as
described in 7.1.14.

DTMF Event Symbol

d0 "0"
d1 "1"
d2 "2"

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

E.6.1 Properties

None.

E.6.2 Events

DTMF digits

EventIds are defined with the same names as the SignalIds defined
in the table found in E.5.3.

DigitMap Completion Event
EventID: ce, 0x0004

Generated when a digit map completes as described in 7.1.14.

EventsDescriptor parameters: None.

ObservedEventsDescriptor parameters:

DigitString
ParameterID: ds (0x0001)

Type: string of digit map symbols (possibly empty) returned
as a quotedString

Possible values: a sequence of the characters "0" through
"9", "A" through "F", and the long duration modifier "Z".

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

Termination Method
ParameterID: Meth (0x0003)

Type: enumeration

Possible values:

"UM" (0x0001) Unambiguous match

"PM" (0x0002) Partial match, completion by timer expiry
or unmatched event

"FM" (0x0003) Full match, completion by timer expiry or
unmatched event

Description: indicates the reason for generation of the
event. See the procedures in 7.1.14.

E.6.3 Signals

None.

E.6.4 Statistics

None.

E.6.5 Procedures

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

E.7 Call Progress Tones Generator Package

PackageID: cg, 0x0007
Version: 1
Extends: tonegen version 1

This package defines the basic call progress tones as signals and
extends the allowed values of the tl parameter of playtone in
tonegen.

E.7.1 Properties

None.

E.7.2 Events

None.

E.7.3 Signals

Dial Tone
SignalID: dt (0x0030)

Generate dial tone. The physical characteristic of dial tone is
available in the gateway.

Signal Type: TimeOut

Duration: Provisioned

Additional parameters:

None.

Additional values:

dt (0x0030) is defined as a tone id for playtone

The other tones of this package are defined in exactly the same way.
A table with all signal names and signal IDs is included. Note that
each tone is defined as both a signal and a tone id, thus extending
the basic tone generation package.

Signal Name Signal ID/tone id

Dial Tone dt (0x0030)
Ringing Tone rt (0x0031)
Busy Tone bt (0x0032)
Congestion Tone ct (0x0033)
Special Information Tone sit(0x0034)
Warning Tone wt (0x0035)
Payphone Recognition Tone prt (0x0036)
Call Waiting Tone cw (0x0037)
Caller Waiting Tone cr (0x0038)

E.7.4 Statistics

None.

E.7.5 Procedures

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

E.8 Call Progress Tones Detection Package

PackageID: cd (0x0008)
Version: 1
Extends: tonedet version 1

This package defines the basic call progress detection tones. This
package extends the possible values of tone id in the "start tone
detected", "end tone detected" and "long tone detected" events.

Additional values

toneID values are defined for start tone detected, end tone
detected and long tone detected with the same values as those in
package cg (call progress tones generation package).

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

E.8.1 Properties

None.

E.8.2 Events

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

E.8.3 Signals

None.

E.8.4 Statistics

None.

E.8.5 Procedures

None.

E.9 Analog Line Supervision Package

PackageID: al, 0x0009
Version: 1
Extends: None

This package defines events and signals for an analog line.

E.9.1 Properties

None.

E.9.2 Events

onhook
EventID: on (0x0004)

Detects handset going on hook. Whenever an events descriptor is
activated that requests monitoring for an on-hook event and the
line is already on-hook, then the MG shall behave according to the
setting of the "strict" parameter.

EventDescriptor parameters:

Strict Transition
ParameterID: strict (0x0001)

Type: enumeration

Possible values: "exact" (0x00), "state" (0x01), "failWrong"
(0x02)

"exact" means that only an actual hook state transition to
on-hook is to be recognized;

"state" means that the event is to be recognized either if
the hook state transition is detected or if the hook state
is already on-hook;

"failWrong" means that if the hook state is already
on-hook, the command fails and an error is reported.

ObservedEventsDescriptor parameters:

Initial State
ParameterID: init (0x0002)

Type: Boolean

Possible values:

"True" means that the event was reported because the line
was already on-hook when the events descriptor containing
this event was activated;

"False" means that the event represents an actual state
transition to on-hook.

offhook
EventID: of (0x0005)

Detects handset going off hook. Whenever an events descriptor is
activated that requests monitoring for an off-hook event and the
line is already off-hook, then the MG shall behave according to
the setting of the "strict" parameter.

EventDescriptor parameters:

Strict Transition
ParameterID: strict (0x0001)

Type: enumeration

Possible values: "exact" (0x00), "state" (0x01), "failWrong"
(0x02)

"exact" means that only an actual hook state transition
to off-hook is to be recognized;

"state" means that the event is to be recognized either
if the hook state transition is detected or if the hook
state is already off-hook;

"failWrong" means that if the hook state is already off-
hook, the command fails and an error is reported.

ObservedEventsDescriptor parameters

Initial State
ParameterID: init (0x0002)

Type: Boolean

Possible values:

"True" means that the event was reported because the line
was already off-hook when the events descriptor
containing this event was activated;

"False" means that the event represents an actual state
transition to off-hook.

flashhook
EventID: fl, 0x0006

Detects handset flash. A flash occurs when an onhook is followed
by an offhook between a minimum and maximum duration.

EventDescriptor parameters:

Minimum duration
ParameterID: mindur (0x0004)

Type: integer in milliseconds

Default value is provisioned.

Maximum duration
ParameterID: maxdur (0x0005)

Type: integer in milliseconds

Default value is provisioned.

ObservedEventsDescriptor parameters:

None

E.9.3 Signals

ring
SignalID: ri, 0x0002

Applies ringing on the line

Signal Type: TimeOut

Duration: Provisioned

Additional parameters:

Cadence
ParameterID: cad (0x0006)

Type: list of integers representing durations of alternating
on and off segments, constituting a complete ringing cycle
starting with an on. Units in milliseconds

Default is fixed or provisioned. Restricted function MGs
may ignore cadence values they are incapable of generating.

Frequency
ParameterID: freq (0x0007)

Type: integer in Hz

Default is fixed or provisioned. Restricted function MGs
may ignore frequency values they are incapable of
generating.

E.9.4 Statistics

None.

E.9.5 Procedures

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

E.9.6 Error code

This package defines a new error code:

540 - Unexpected initial hook state

The procedure for use of this code is given in E.9.5.

E.10 Basic Continuity Package

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

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 E.10.5
for further explanation.

Signal Type: On/Off

Default duration is provisioned

Additional parameters:

None.

E.10.4 Statistics

None.

E.10.5 Procedures

When a MGC wants to initiate a continuity test, it sends a command to
the MG containing:

- 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 and any other required
conditions are satisfied before the signal times out, the cmp event
shall be generated with the value of the result parameter equal to
success. In all other cases, the cmp event shall be generated with
the value of the result parameter equal to failure.

When a MGC wants the MG to respond to a continuity test, it sends a
command to the MG containing a signals descriptor with the rsp
signal. Upon reception of a command with the rsp signal, the MG
either applies a loopback or (for 2-wire circuits) awaits reception
of a continuity test tone. In the loopback case, any incoming
information shall be reflected back as outgoing information. In the
2-wire case, any time the appropriate test tone is received, the
appropriate response tone should be sent. The MGC determines when to
remove the rsp signal.

When a continuity test is performed on a Termination, no echo devices
or codecs shall be active on that Termination.

Performing voice path assurance as part of continuity testing is
provisioned by bilateral agreement between network operators.

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

E.11 Network Package

PackageID: nt (0x000b)
Version: 1
Extends: None

This package defines properties of network terminations independent
of network type.

E.11.1 Properties

Maximum Jitter Buffer
PropertyID: jit (0x0007)

This property puts a maximum size on the jitter buffer.

Type: integer in milliseconds

Possible values: This property is specified in milliseconds.

Defined in: LocalControlDescriptor

Characteristics: read/write

E.11.2 Events

network failure
EventID: netfail, 0x0005

The termination generates this event upon detection of a failure
due to external or internal network reasons.

EventDescriptor parameters

None.

ObservedEventsDescriptor parameters

cause
ParameterID: cs (0x0001)

Type: string

Possible values: any text string

This parameter may be included with the failure event to
provide diagnostic information on the reason of failure.

quality alert
EventID: qualert, 0x0006

This property allows the MG to indicate a loss of quality of the
network connection. The MG may do this by measuring packet loss,
interarrival jitter, propagation delay and then indicating this
using a percentage of quality loss.

EventDescriptor parameters

Threshold
ParameterId: th (0x0001)

Type: integer

Possible values: 0 to 99

Description: threshold for percent of quality loss measured,
calculated based on a provisioned method, that could take
into consideration packet loss, jitter, and delay for
example. Event is triggered when calculation exceeds the
threshold.

ObservedEventsDescriptor parameters

Threshold
ParameterId: th (0x0001)

Type: integer

Possible values: 0 to 99

Description: percent of quality loss measured, calculated
based on a provisioned method, that could take into
consideration packet loss, jitter, and delay for example.

E.11.3 Signals

None.

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) [RFC1889].

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

ParameterName: rtppayload
ParameterID: rtppltype, 0x01

Type: list of enumerated types.

Possible values: The encoding method shall be specified by
using one or several valid encoding names, as defined in the
RTP AV Profile or registered with IANA.

E.12.3 Signals

None.

E.12.4 Statistics

Packets Sent
StatisticID: ps (0x0004)

Type: double

Possible values: any 64-bit integer

Packets Received
StatisticID: pr (0x0005)

Type: double

Possible values: any 64-bit integer

Packet Loss
StatisticID: pl (0x0006)

Describes the current rate of packet loss on an RTP stream, as
defined in IETF RFC1889. 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 RFC1889. Jitter measures the variation
in interarrival time for RTP data packets.

Delay
StatisticID:delay (0x0008)

Requests the current value of packet propagation delay expressed
in timestamp units. Same as average latency.

E.12.5 Procedures

None.

E.13 TDM Circuit Package

PackageID: tdmc (0x000d)
Version: 1
Extends: Network Package version 1

This package may be used by any termination that supports gain and
echo control. It was originally intended for use on TDM circuits
but may be more widely used.

New versions or extensions of this package should take non-TDM use
into account.

E.13.1 Properties

Echo Cancellation
PropertyID: ec (0x0008)

Type: boolean

Possible values:

"on" (when the echo cancellation is requested) and

"off" (when it is turned off.)

The default is provisioned.

Defined in: LocalControlDescriptor

Characteristics: read/write

Gain Control
PropertyID: gain (0x000a)

Gain control, or usage of of signal level adaptation and
noise level reduction is used to adapt the level of the signal.
However, it is necessary, for example for modem calls, to turn
off this function.

Type: integer

Possible values:

The gain control parameter may either be specified as
"automatic" (0xffffffff), or as an explicit number of decibels
of gain (any other integer value). The default is provisioned
in the MG.

Defined in: LocalControlDescriptor

Characteristics: read/write

E.13.2 Events

None.

E.13.3 Signals

None.

E.13.4 Statistics

None.

E.13.5 Procedures

None.

APPENDIX I EXAMPLE CALL FLOWS (INFORMATIVE)

All H.248.1 implementors must read the normative part of this RFC
carefully before implementing from it. The examples in this appendix
should not be used as stand-alone explanations of how to create
protocol messages.

The examples in this appendix use SDP for encoding of the Local and
and Remote stream descriptors. SDP is defined in RFC2327. If there
is is any discrepancy between the SDP in the examples, and RFC2327,
the the RFCshould be consulted for correctness. Audio profiles used
are are those defined in IETF RFC1890, and others registered with
IANA. For example, G.711 A-law is called PCMA in SDP, and is
assigned profile 0. G.723.1 is called G723 and is profile 4; H.263 is
called H263 and is profile 34. See also
http://www.iana.org/assignments/rtp-parameters.

A.1 Residential Gateway to Residential Gateway Call

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

A.1.1 Programming Residential GW Analog Line Terminations for Idle
Behavior

The following illustrates the API invocations from the Media Gateway
Controller and Media Gateways to get the Terminations in this
scenario programmed for idle behavior. Both the originating and
terminating Media Gateways have idle AnalogLine Terminations
programmed to look for call initiation events (i.e., -offhook) by
using the Modify Command with the appropriate parameters. The null
Context is used to indicate that the Terminations are not yet
involved in a Context. The ROOT termination is used to indicate the
entire MG instead of a termination within the MG.

In this example, MG1 has the IP address 124.124.124.222, MG2 is
125.125.125.111, and the MGC is 123.123.123.4. The default Megaco
port is 55555 for all three.

1. An MG registers with an MGC using the ServiceChange command:

MG1 to MGC:

MEGACO/1 [124.124.124.222] Transaction = 9998 {
Context = - {

ServiceChange = ROOT {Services {
Method=Restart,
ServiceChangeAddress=55555, Profile=ResGW/1}
}
} }

2. The MGC sends a reply:

MGC to MG1:

MEGACO/1 [123.123.123.4]:55555 Reply = 9998 {
Context = - {ServiceChange = ROOT {
Services {ServiceChangeAddress=55555, Profile=ResGW/1} } } }

3. The MGC programs a Termination in the NULL context. The
terminationId is A4444, the streamId is 1, the requestId in the
Events descriptor is 2222. The mId is the identifier of the sender
of this message, in this case, it is the IP address and port
[123.123.123.4]:55555. Mode for this stream is set to SendReceive.
"al" is the analog line supervision package. Local and Remote are
assumed to be provisioned.

MGC to MG1:

MEGACO/1 [123.123.123.4]:55555 Transaction = 9999 {
Context = - {
Modify = A4444 {
Media { Stream = 1 {
LocalControl {
Mode = SendReceive,
tdmc/gain=2, ; in dB,
tdmc/ec=on
},

}
},
Events = 2222 {al/of(strict=state)}
}
} }

The dialplan script could have been loaded into the MG previously.
Its function would be to wait for the OffHook, turn on dialtone and
start collecting DTMF digits. However in this example, we use the
digit map, which is put into place after the offhook is detected
(step 5 below).

Note that the embedded EventsDescriptor could have been used to
combine steps 3 and 4 with steps 8 and 9, eliminating steps 6 and 7.

4. The MG1 accepts the Modify with this reply:

MG1 to MGC:

MEGACO/1 [124.124.124.222]:55555

Reply = 9999 {
Context = - {Modify = A4444} }

5. A similar exchange happens between MG2 and the MGC, resulting in
an idle Termination called A5555.

A.1.2 Collecting Originator Digits and Initiating Termination

The following builds upon the previously shown conditions. It
illustrates the transactions from the Media Gateway Controller and
originating Media Gateway (MG1) to get the originating Termination
(A4444) through the stages of digit collection required to initiate a
connection to the terminating Media Gateway (MG2).

6. MG1 detects an offhook event from User 1 and reports it to the
Media Gateway Controller via the Notify Command.

MG1 to MGC:

MEGACO/1 [124.124.124.222]:55555 Transaction = 10000 {
Context = - {
Notify = A4444 {ObservedEvents =2222 {
19990729T22000000:al/of(init=false)}}
} }

7. And the Notify is acknowledged.

MGC to MG1:

MEGACO/1 [123.123.123.4]:55555 Reply = 10000 {

Context = - {Notify = A4444} }

8. The MGC Modifies the termination to play dial tone, to look for
digits according to Dialplan0 and to look for the on-hook event now.

MGC to MG1:

MEGACO/1 [123.123.123.4]:55555 Transaction = 10001 {
Context = - {
Modify = A4444 {
Events = 2223 {
al/on(strict=state), dd/ce {DigitMap=Dialplan0}
},
Signals {cg/dt},
DigitMap= Dialplan0{ (0 00[1-
7]xxx8xxxxxxxFxxxxxxxExx91xxxxxxxxxx9011x.)}
}
} }

9. And the Modify is acknowledged.

MG1 to MGC:

MEGACO/1 [124.124.124.222]:55555 Reply = 10001 {
Context = - {Modify = A4444} }

10. Next, digits are accumulated by MG1 as they are dialed by User
1. Dialtone is stopped upon detection of the first digit. When an
appropriate match is made of collected digits against the currently
programmed Dialplan for A4444, another Notify is sent to the Media
Gateway Controller.

MG1 to MGC:

MEGACO/1 [124.124.124.222]:55555 Transaction = 10002 {
Context = - {
Notify = A4444 {ObservedEvents =2223 {
19990729T22010001:dd/ce{ds="916135551212",Meth=UM}}}
} }

11. And the Notify is acknowledged.

MGC to MG1:

MEGACO/1 [123.123.123.4]:55555 Reply = 10002 {
Context = - {Notify = A4444} }

12. The controller then analyses the digits and determines that a
connection needs to be made from MG1 to MG2. Both the TDM

termination A4444, and an RTP termination are added to a new context
in MG1. Mode is ReceiveOnly since Remote descriptor values are not
yet specified. Preferred codecs are in the MGC's preferred order of
choice.

MGC to MG1:

MEGACO/1 [123.123.123.4]:55555 Transaction = 10003 {
Context = $ {
Add = A4444,
Add = $ {
Media {
Stream = 1 {
LocalControl {
Mode = ReceiveOnly,

nt/jit=40 ; in ms
},
Local { v=0 c=IN IP4 $ m=audio $ RTP/AVP 4
a=ptime:30 v=0 c=IN IP4 $ m=audio $ RTP/AVP 0
}
}
}
}
} }

NOTE - The MGC states its preferred parameter values as a series
of SDP blocks in Local. The MG fills in the Local Descriptor in
the Reply.

13. MG1 acknowledges the new Termination and fills in the Local IP
address and UDP port. It also makes a choice for the codec based on
the MGC preferences in Local. MG1 sets the RTP port to 2222.

MG1 -> MGC:

MEGACO/1 [124.124.124.222]:55555 Reply = 10003 {
Context = 2000 {
Add = A4444,
Add=A4445{
Media {
Stream = 1 {
Local { v=0 o=- 2890844526 2890842807 IN IP4
124.124.124.222 s=- t= 0 0 c=IN IP4 124.124.124.222 m=audio 2222
RTP/AVP 4 a=ptime:30 a=recvonly
} ; RTP profile for G.723.1 is 4
}

}
}
} }

14. The MGC will now associate A5555 with a new Context on MG2, and
establish an RTP Stream (i.e., A5556 will be assigned), SendReceive
connection through to the originating user, User 1. The MGC also
sets ring on A5555.

MGC to MG2:

MEGACO/1 [123.123.123.4]:55555 Transaction = 50003 {
Context = $ {
Add = A5555 { Media {
Stream = 1 {
LocalControl {Mode = SendReceive} }},
Events=1234{al/of(strict=state)},
Signals {al/ri}

},
Add = $ {Media {
Stream = 1 {
LocalControl {
Mode = SendReceive,
nt/jit=40 ; in ms
},
Local { v=0 c=IN IP4 $ m=audio $ RTP/AVP 4
a=ptime:30
},
Remote { v=0 c=IN IP4 124.124.124.222 m=audio 2222
RTP/AVP 4 a=ptime:30
} ; RTP profile for G.723.1 is 4
}
}
}
} }

15. This is acknowledged. The stream port number is different from
the control port number. In this case it is 1111 (in the SDP).

MG2 to MGC:

MEGACO/1 [125.125.125.111]:55555 Reply = 50003 {
Context = 5000 {
Add = A5555,
Add = A5556{
Media {
Stream = 1 {

Local { v=0 o=- 7736844526 7736842807 IN IP4
125.125.125.111 s=- t= 0 0 c=IN IP4 125.125.125.111 m=audio 1111
RTP/AVP 4 }
} ; RTP profile for G723.1 is 4
}
}

} }

16. The above IPAddr and UDPport need to be given to MG1 now.

MGC to MG1:

MEGACO/1 [123.123.123.4]:55555 Transaction = 10005 {
Context = 2000 {
Modify = A4444 {
Signals {cg/rt}
},
Modify = A4445 {
Media {
Stream = 1 {
Remote { v=0 o=- 7736844526 7736842807 IN IP4
125.125.125.111 s=- t= 0 0 c=IN IP4 125.125.125.111 m=audio 1111
RTP/AVP 4
}
} ; RTP profile for G723.1 is 4
}
}
} }

MG1 to MGC:

MEGACO/1 [124.124.124.222]:55555 Reply = 10005 {
Context = 2000 {Modify = A4444, Modify = A4445} }

17. The two gateways are now connected and User 1 hears the
RingBack. The MG2 now waits until User2 picks up the receiver and
then the two-way call is established.

From MG2 to MGC:

MEGACO/1 [125.125.125.111]:55555 Transaction = 50005 {
Context = 5000 {

Notify = A5555 {ObservedEvents =1234 {
19990729T22020002:al/of(init=false)}}
} }

From MGC to MG2:

MEGACO/1 [123.123.123.4]:55555 Reply = 50005 {
Context = - {Notify = A5555} }

From MGC to MG2:

MEGACO/1 [123.123.123.4]:55555 Transaction = 50006 {
Context = 5000 {
Modify = A5555 {
Events = 1235 {al/on(strict=state)},
Signals { } ; to turn off ringing
}
} }

From MG2 to MGC:

MEGACO/1 [125.125.125.111]:55555 Reply = 50006 {
Context = 5000 {Modify = A4445} }

18. Change mode on MG1 to SendReceive, and stop the ringback.

MGC to MG1:

MEGACO/1 [123.123.123.4]:55555 Transaction = 10006 {
Context = 2000 {
Modify = A4445 {
Media {
Stream = 1 {
LocalControl {
Mode=SendReceive

}
}
}
},
Modify = A4444 {
Signals { }
}

} }

from MG1 to MGC:

MEGACO/1 [124.124.124.222]:55555 Reply = 10006 {
Context = 2000 {Modify = A4445, Modify = A4444}}

19. The MGC decides to Audit the RTP termination on MG2.

MGC -> MG2:

MEGACO/1 [123.123.123.4]:55555 Transaction = 50007 {
Context = - {AuditValue = A5556{
Audit{Media, DigitMap, Events, Signals, Packages, Statistics }}
} }

20. The MG2 replies.

MG2 -> MGC:

MEGACO/1 [125.125.125.111]:55555 Reply = 50007 {
Context = - { AuditValue = A5556 {
Media {
TerminationState { ServiceStates = InService,
Buffer = OFF },
Stream = 1 {
LocalControl { Mode = SendReceive,
nt/jit=40 },
Local { v=0 o=- 7736844526 7736842807 IN IP4
125.125.125.111 s=- t= 0 0 c=IN IP4 125.125.125.111 m=audio 1111
RTP/AVP 4 a=ptime:30
},
Remote { v=0 o=- 2890844526 2890842807 IN IP4
124.124.124.222 s=- t= 0 0 c=IN IP4 124.124.124.222 m=audio 2222
RTP/AVP 4 a=ptime:30
} } },
Events,
Signals,
DigitMap,
Packages {nt-1, rtp-1},
Statistics { rtp/ps=1200, ; packets sent
nt/os=62300, ; octets sent
rtp/pr=700, ; packets received
nt/or=45100, ; octets received
rtp/pl=0.2, ; % packet loss
rtp/jit=20,
rtp/delay=40 } ; avg latency
}

} }

21. When the MGC receives an onhook signal from one of the MGs, it
brings down the call. In this example, the user at MG2 hangs up
first.

From MG2 to MGC:

MEGACO/1 [125.125.125.111]:55555 Transaction = 50008 {
Context = 5000 {
Notify = A5555 {ObservedEvents =1235 {
19990729T24020002:al/on(init=false)}
}
} }

From MGC to MG2:

MEGACO/1 [123.123.123.4]:55555 Reply = 50008 {

Context = - {Notify = A5555} }

22. The MGC now sends both MGs a Subtract to take down the call.
Only the subtracts to MG2 are shown here. Each termination has its
own set of statistics that it gathers. An MGC may not need to
request both to be returned. A5555 is a physical termination, and
A5556 is an RTP termination.

From MGC to MG2:

MEGACO/1 [123.123.123.4]:55555 Transaction = 50009 {
Context = 5000 {
Subtract = A5555 {Audit{Statistics}},
Subtract = A5556 {Audit{Statistics}}
} }

From MG2 to MGC:

MEGACO/1 [125.125.125.111]:55555 Reply = 50009 {
Context = 5000 {
Subtract = A5555 {
Statistics {
nt/os=45123, ; Octets Sent
nt/dur=40 ; in seconds
}
},
Subtract = A5556 {
Statistics {
rtp/ps=1245, ; packets sent

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.

APPENDIX II Changes From RFC3015

In the following table, "source" indicates when the change was first
approved. It has the following values:

IG1100: H.248 Implementor's Guide approved in November, 2000 (as TD
Plen-39, Christian Groves, editor).

IG0601: H.248 Implementor's Guide approved in June, 2001 (as TD
Plen-15, Christian Groves, editor).

IGDUB: Draft H.248 Implementor's Guide approved at the Q.3
Rapporteur's meeting held near Dublin, October 2001 (as TD-28, Terry
Anderson, editor).

GEN0202: added at the Geneva meeting, February 2002, which consented
to H.248 v1 Amendment 1 (as TD Plen-36r1, Marcello Pantaleo, editor).

ITUPOST: added in post-Geneva editing by the ITU-T.

TTPOST: added in post-approval editing by the Megaco Chair, Tom
Taylor, who assembled this document for submission.

Section Source Change

1 ITUPOST Reference changed from H.248 to H.248.1.

2.1 ITUPOST Reference added for error codes, changed from
H.248 Annex L to H.248.8 (2002).

2.1 IG1100 Corrected Q.765 reference to Q.765.5.

2.1 GEN0202 Added reference to X.690.

2.2 GEN0202 Added reference to H.226.

2.2 IGDUB Added informative references to Q.724, Q.764,
and Q.1902.4.

4 IG0601 Added expansion of ALF.

5 TTPOST Gave priority to IETF conventions (added at
start of document).

6.1.1 IG0601 Added text regarding use of wildcards for
context identifiers. (This information
already appeared in section 8.1.2. The IG
change subsequently disappeared.)

6.1.1 IG1100 Added ranking of priority values.

6.2 IGDUB Deleted definition of signals.

6.2 GEN0202 Expanded text and diagrams describing
multiplexing terminations.

6.2 TTPOST Added asterisks to multiplexing diagrams to
indicate centre of context. Added Figure 6a
showing cascading of multiplexes.

6.2.2 IG0601 Added text indicating that ALL does not
include ROOT.

6.2.3 IG1100 Added text clarifying what must be supported
to claim support of a package.

6.2.3 IG1100 Added text indicating what packages a peer can
indicate support for, when some of them are
extensions of others.

6.2.4 IG0601 Added text on ability of provisioning to
override default values, and need for MGC to
audit to learn the provisioned defaults.

6.2.4 IG0601 Added text indicating effect of omitting
specific properties from Descriptors in
commands modifying a termination.
Contradicted original text saying that omitted
properties retain their prior values (still
true for entirely-omitted Descriptors).

6.2.4 GEN0202 Modified above text to restrict it to
read/write properties, allow for default
behaviour in place of default values if so
specified in the property definition.

6.2.4 IGDUB Trimmed definition of signals Descriptor in
table and inserted cross-reference to section
7.1.11.

6.2.4 IG1100 Added Topology and Error Descriptors to table.

6.2.5 IGDUB Specified error code to return if ROOT used
inappropriately.

7.1.1 IG1100 Added qualification to explanation of effect
of missing Audit Descriptor, excepting
Subtract.

7.1.3 GEN0202 Changed "inputs" to "bearers" to be consistent
with terminology in 6.2.

7.1.4 IG0601 Small change to make clear that more than one
of Local, Remote, and LocalControl can be
included in the default streamId.

7.1.7 IG0601 Default value for Mode specified to be
Inactive.

7.1.7 GEN0202 Added text requiring processing of media in
any of the reserved formats, where more than
one has been reserved in a given stream.

7.1.8 IGDUB Added restriction to at most one m= line per
session description.

7.1.9 IG0601 Text added to omit request identifier if the
EventsDescriptor is empty. Further text added
at end to indicate the effects of an empty
EventsDescriptor and an empty
EventBufferDescriptor.

7.1.9 IG0601 Fixed typo for destination of a Notify.

7.1.9 IG1100 Added note to say event remains active after
it has been notified, so long as it is still
present in the active Events Descriptor.

7.1.11 IGDUB Added definition of signals.

7.1.11 GEN0202 Modified definition to include example of more
complex signal, and added role of signal in
media preparation for future signals.

7.1.11 IGDUB The timeout completion reason was broadened to
include other circumstances where the signal
completed on its own. Text added to indicate
that if default signal type changed to TO,
duration parameter must be provided.

7.1.11 GEN0202 Removed reference to BR signal being "so
short" it will stop on its own. Added text
indicating that if the type of a signal is
changed to TO, the Duration parameter must be
supplied.

7.1.11 IG1100 Deleted text discussing type of Signals List.

7.1.12 GEN0202 Improved wording of introductory paragraph and
added text making content of returned
Descriptor clear.

7.1.14.2 GEN0202 Added text indicating that when the start
timer is set to 0, initial digit timing is
disabled and the MG waits indefinitely for
digits.

7.1.14.2 GEN0202 Added text pointing out that default digit
timer values should be provisioned, but can be
overridden in the digit map.

7.1.14.3 GEN0202 Changed result of long-short digit timer
conflict from undefined to long.

7.1.14.6 IG1100 Clarified that the digit map is provided by
the eventDM parameter, which must be present.

7.1.14.7 GEN0202 Added text clarifying that events covered by
the digit map completion event have no side-
effects unless separately enabled.

7.1.14.8 IG0601 Added requirement that the event specification
include the eventDM parameter.

7.1.17 IGDUB Added text to indicate timestamp is optional
and to include observed event parameters in
reported content.

7.1.17 GEN0202 Deleted provision that time is expressed in
UTC (since intention was to use format, not
time zone).

7.1.18 IGDUB Added text indicating error to return if
topology option not supported.

7.1.18 IG1100 Added text clarifying effect of not mentioning
TTPOST a termination in a topology Descriptor, and
default topology for a new termination. (This
text got lost between the Dublin meeting and
the production of H.248 Amendment 1 out of the
Geneva 02/02 meeting. It has been added back
to the present document.)

7.1.19 IG1100 New section to describe Error Descriptor.
GEN0202 Slightly edited in Geneva 02/02 meeting.
ITUPOST Reference for error code documentation updated
to H.248.8.

7.1.19 IG0601 Added paragraph giving guidance on level at
which errors should be reported.

7.2 IG1100 Noted possibility of Error Descriptor in reply
to any command.

7.2.1 IG1100 Added EventBufferDescriptor as Add parameter.

7.2.1 IG1100 Removed restriction on use of CHOOSE wildcard.

7.2.2 IG1100 Added EventBufferDescriptor as Modify
parameter.

7.2.2 GEN0202 Added text on side-effects of Modify of a
multiplexing termination.

7.2.3 IG1100 Added prohibition against subtracting from the
NULL context.

7.2.3 GEN0202 Added text on side-effects of Subtract of a
multiplexing termination.

7.2.3 IGDUB Added text clarifying effect of empty
AuditDescriptor in Subtract.

7.2.4 IG1100 Added EventBufferDescriptor as Move parameter.

7.2.4 GEN0202 Removed misleading statement that Move acts as
subtract from original context.

7.2.4 IG1100 Clarified effect of Move on properties of the
moved termination.

7.2.4 GEN0202 Added text on side-effects of Move of a
multiplexing termination.

7.2.5 IG1100 Added examples showing W- wildcard usage.

7.2.5 IG1100 Noted that returning a list of all contextIDs
requires that they be returned one per
ActionReply.

7.2.5 IG1100 Added table entry (ALL, specific) to determine
context in which termination currently
resides.

7.2.6 GEN0202 Added table similar to that in 7.2.5.

7.2.7 IG0601 Added TerminationID to API.

7.2.7 IGDUB Indicated timestamp was optional in Notify, to
accord with syntax.

7.2.7 IG1100 Noted possibility of sending Error Descriptor
in Notify.

7.2.8 IG0601 Added text to description of Forced method to
indicate that Forced on ROOT indicates a cold
restart (all context state lost).

7.2.8 IGDUB Amplified explanation of Disconnected method
to emphasize return to the previously
controlling MGC.

7.2.8 IG0601 Added text for MG use of Failover method when
it detects MGC failure.

7.2.8 IG1100 Added notes discouraging use of
ServiceChangeAddress and warning that it could
be either a full address or just a port
number.

7.2.8 IG0601 Added text indicating that timestamp does not
necessarily represent absolute time, only
local clock reading.

7.2.8 IGDUB Corrected "gateway" to "MGC" in discussion of
returned ServiceChangeMgcId parameter.

7.3 IG0601 Removed error code documentation to Annex L
ITUPOST (now H.248.8).

8 IG1100 Added requirement that an Action be non-empty.

8 GEN0202 Added context properties and context property
audit requests to commands as potential
contents of actions.

8.1.2 GEN0202 Added prohibition on using partial contextIDs
with ALL wildcards.

8.2.2 IG1100 Added text clarifying when in transaction
processing the requested actions have been
completed and a reply can be sent.

8.2.2 IG1100 Added ALL as allowed contextID in
TransactionReply.

8.2.2 GEN0202 Provided general reference to section 7.1.19
for generation of error Descriptors.

8.2.2 IG0601 Corrected Actions to Commands when discussing
partially-understood action.

8.3 IG0601 Added text specifying that the same MId value
must be used by a given entity throughout the
life of a control association.

8.3 IG0601 Added text expanding on independence of
transactions from messages.

9 ITUPOST Indicated that additional transports may be
defined in separate Recommendations as well as
annexes to the primary specification.

9 IG0601 Gave specific example of "request source
address" for IP.

9.1 IG1100 Deleted restriction to one outstanding Notify
command on a termination at one time, since
this is transport-specific.

9.1 IG0601 Restored restriction, but noted that it
applied only to transport not guaranteeing
ordered delivery.

10.2 IG1100 Corrected length of synthesized address field
from 10 to 20 hex digits and indicated that
calculation should be over entire message, not
just one transaction.

11.2 IG1100 Corrected text in first two paragraphs
describing use of ServiceChangeMgcId
parameter.

11.2 IG1100 Corrected "Transaction Accept" to "Transaction
Reply".

11.4 IG0601 Noted that support of redundant MGs requires
GEN0202 use of a reliable transport and support in the
MGC. Added more explanation in Geneva.

11.5 IG0601 Added text clarifying procedure if MG unable
to establish a control relationship with any
of its eligible MGCs.

11.5 IGDUB Added text indicating that when trying to
reestablish contact with the previously
controlling MGC the MG uses the Disconnected
method.

11.5 IG1100 Clarified handoff procedure.

11.5 GEN0202 Changed text on replies to transactions in
progress during handoff. Replies now
discarded when the service relationship with
the old MGC has ended, rather than sent to the
new MGC. The new MGC could still send replies
to requests sent to the old MGC.

12.1.1 GEN0202 Added optional package designation as
"designed to be extended only".

12.1.1 IG1100 Made prohibition on overloading of identifiers
in extended packages transitive through all
ancestors of the extended package.

12.1.2 IGDUB Clarified the set of types allowed for
properties.

12.1.2 GEN0202 Added requirement to specify the base type of
a sub-list.

12.1.2 GEN0202 Provided requirements for content of the
"Possible Values" template item, including
specification of default values or behaviour.

12.1.4 GEN0202 Added requirement to specify the default
signal type, and specify a default duration
for TO signals. Also noted that duration is
meaningless for BR, and that the signal type
might be dependent on the values of other
signal parameters.

12.2 GEN0202 Fixed section title (covers only event and
signal parameters, not properties or
statistics).

12.2 IG1100 Reserved SPA and EPA prefixes, so they are not
to be used for signal and event parameter
tokens.

12.2 IG0601 Expanded list of reserved prefixes.

12.2 IGDUB Clarified the set of types allowed for signal
and event parameters.

12.2 GEN0202 Added requirement to specify the base type of
a sub-list.

12.2 GEN0202 Provided requirements for content of the
"Possible Values" template item, including
specification of default values or behaviour.

12.4 IGDUB Corrected to indicate identifiers must start
with alphabetic rather than alphanumeric
character.

13.1 IG0601 Changed private range of binary package
identifiers to convenient hex values.

A GEN0202 Removed versions from X.680 and X.690
references.

A.2 IGDUB Added note warning that the syntax alone does
not provide a complete description of the
constraints, but must be supplemented by a
reading of the text and comments.

A.2 IG0601 Added description of double wrapping of
parameters declared as OCTET STRING.

A.2 GEN0202 Some editing of double wrapping description to
use ASN.1, BER in their proper places. Added
possibility of encoding strings as UTF8String,
but only if they contain non-ASCII characters.

A.2 IGDUB Added line in table on double wrapping of true
octet strings.

A.2 IG1100 Corrected and expanded comments describing
mtpAddress form of MId. Fixed maximum length
of mtpAddress both here and in
ServiceChangeAddress.

A.2 IG0601 Inserted missing lines in IP4Address
production.

A.2 IG0601 Modified TransactionResponseAck to allow
acknowledgement of multiple ranges of
transactionIds.

A.2 IG0601 Corrected numerical value of CHOOSE as a
context identifier.

A.2 IGDUB Added missing extension marker in
TopologyRequest.

A.2 IG1100 AuditReply and AuditResult modified to bring
binary functionality into line with text
functionality.

A.2 IG0601 Removed OPTIONAL tag from terminationID in
NotifyReply.

A.2 IG0601 Added extraInfo substructure to EventParameter
and SigParameter.

A.2 IG0601 Modified MediaDescriptor to make it optional
to specify a stream.

A.2 IG0601 Added OPTIONAL tags to reserveValue and
reserveGroup.

A.2 IGDUB Added to comments for pkgdName to indicate
applicability to event names, signal names,
and statisticIds as well as property.

A.2 IG0601 RequestID made optional in EventsDescriptor
and SecondEventsDescriptor and comment added
saying it must be present if events are
present.

A.2 IG1100 Added OPTIONAL tags on RequestActions and
SecondRequestedActions keepActive BOOLEANs.

A.2 IG1100 Added comment to indicate requestID value to
use in an AuditCapReply.

A.2 GEN0202 Added comment to DigitMapValue indicating time
units for timers.

A.2 IG0601 Added comment indicating coding of Value for
GEN0202 ServiceChangeReason. Cleaned up in Geneva to
use ASN.1 and BER in their proper places.

A.2 IG0601 Inserted missing extension marker in
ServiceChangeParm production.

A.2 IG0601 Aligned definition of mtpAddress in
ServiceChangeAddress with that in MId.

A.2 IG0601 Added timestamp to ServiceChangeResParm.

A.2 IGDUB Changed type of profileName in
ServiceChangeProfile to IA5String.

A.2 IG0601 Made returned value optional in
statisticsParameter, to support
auditCapability result.

A.2 GEN0202 Added reference to ISO 8601:1988 for
TimeNotation.

A.2 IG1100 Value production modified to support the
sublist parameter type.

A.3 IG1100 Corrected ABNF for digitStringlisT, replacing
"/" with "".

A.3 IG1100 Added parentheses to digitMapRange production.

A.3 IG1100 Replaced more abbreviated syntax for pathName
with fuller definition and constraints copied
from B.2.

B.2 IGDUB Added note warning that the syntax alone does
not provide a complete description of the
constraints, but must be supplemented by a
reading of the text and comments.

B.2 IG0601 Added note warning that the interpretation of
symbols is context-dependent.

B.2 IG1100 Added comment to indicate case insensitivity
of protocol (excepting SDP) and ABNF.

B.2 IG0601 Expanded upon and capitalized this comment.

B.2 IG0601 Lengthy note added on the coding of the VALUE
construct.

B.2 IGDUB Deleted sentence in note suggesting that
packages could add new types for properties,
parameters, or statistics.

B.2 IG0601 Added note indicating that parsers should
allow for white space preceding the first line
of SDP in Local or Remote.

B.2 IGDUB Added comments identifying the O- and W- tags.

B.2 IG1100 Moved wildcard tag up from individual commands
to commandRequestList.

B.2 GEN0202 Added additional error case to actionReply.

B.2 IG0601 Modified syntax of auditOther to allow return
of terminationID only.

B.2 IGDUB Corrected upper limit for V4hex.

B.2 IG1100 Corrected and expanded comments describing
mtpAddress form of MId.

B.2 IG0601 Modified comment to mediaParm to make
streamParms and StreamDescriptor mutually
exclusive.

B.2 GEN0202 Modified comment further to indicate at most
one instance of terminationStateDescriptor.

B.2 GEN0202 Expanded comment for streamParm to indicate
the restriction on repetition is per item.

B.2 IG0601 Modified "at most once" comments to localParm,
terminationStateParm, and modemType, to allow
multiple instances of propertyParm in the
first two cases and extensionParameter in the
last one.

B.2 IG0601 Added note before description of Local and
Remote, pointing out that the octet value x00
is not allowed in octetString.

B.2 IG0601 Syntax for eventsDescriptor, embedFirst, and
eventBufferDescriptor modified to make
contents beyond token optional.

B.2 IGDUB Replaced "event" by "item" in comment to
pkgdName because pkgdName applies to
properties, signals, and statistics as well.

B.2 IG0601 Corrected placement of EQUAL in eventDM
production.

B.2 IG1100 Added comment and syntax to indicate requestID
value to use in an AuditCapReply.

B.2 IG1100 Corrected Modem Descriptor to allow package
items as properties.

B.2 IG0601 Comment to modemType changed to allow multiple
instances of extensionParameter.

B.2 GEN0202 Comment added to indicate units for Timer.

B.2 IG1100 Added parentheses to digitMapRange production.

B.2 IG1100 Added comment to serviceChangeParm,
restricting each parameter to one appearance.

B.2 IG0601 Added comments making serviceChangeMgcId and
serviceChangeAddress mutually exclusive in
ServiceChangeParm and servChgReplyParm.

B.2 IGDUB Added comment to serviceChangeParm indicating
that ServiceChangeMethod and
ServiceChangeReason are required.

B.2 IG0601 Added Timestamp to servChgReplyParm.

B.2 IG0601 Added comment indicating coding of Value for
ServiceChangeReason.

B.2 IG0601 Modified ServiceChangeAddress to use MId
definition for full address.

B.2 IG1100 Made returned value optional in
statisticsParameter, to support
auditCapability result.

B.2 IG1100 Changed topologyDescriptor to allow multiple
triples.

B.2 IG0601 Added comment forbidding use of a double quote
within a quotedString value.

B.2 IG1100 Reserved prefixes for new tokens added to
signalParameter and eventParameter, to avoid
collision with package names.

B.2 IG1100 EmbedToken and EmergencyToken changed to
remove clash with EventBufferToken.

B.3 IG1100 New section describing hexadecimal octet
encoding.

B.4 IG1100 New section describing hex octet sequence.

C IG1100 Added permission to use Annex C properties in
LocalControl as well as in Local and Remote.

C IG0601 Added text making support of all properties of
Annex C optional.

C IGDUB Added directions to reconcile tabulated
formats with allowed types for properties.

C.1 IG1100 Corrected Q.765 reference to Q.765.5 for
ACodec.

C.1 IG1100 Deprecated Echocanc codepoint in favour of
package-defined property.

C.4 ITUPOST Updated references from Q.2961 to Q.2961.1.

C.4 IGDUB Added details on format of VPVC.

C.9 IG1100 Renamed USI to layer1prot.

C.9 IG1100 Deprecated ECHOCI codepoint in favour of
package-defined property.

C.9 IG1100 Added new USI property.

C.11 IG1100 Added m= line tag.

D.1 IG0601 Added explanation of ALF.

D.1.5 IGDUB Expanded text indicating that when trying to
reestablish contact with the previously
controlling MGC the MG uses the Disconnected
method.

E.1.2 GEN0202 Added missing EventsDescriptor parameters
lines.

E.1.2 GEN0202 For the Signal Completion event:
- corrected the description of how it is
enabled
- heavily edited the description of the Signal
Identity observed event parameter and added a
type.

E.1.2 IGDUB The timeout completion reason for the Signal
Completion event was broadened to include
other circumstances where the signal completed
on its own.

E.1.2 IG1100 Added signal list ID observed event parameter
to the Signal Completion event.

E.2.1 IG0601 Added missing read only, read-write
specifications.

E.2.1 IG0601 Split ProvisionalResponseTimer properties into
one for MG, one for MGC.

E.3 GEN0202 Added "Designed to be extended only" to
tonegen package description.

E.4 GEN0202 Added "Designed to be extended only" to
tonedet package description.

E.4.2 GEN0202 Added type for tone ID observed parameter for
Long Tone Detected event.

E.6.2 IG1100 Corrected binary identifier for digit map
completion event to avoid clash with base
package.

E.6.2 IG1100 Removed procedural text.

E.6.5 IG1100 Added procedural text indicating where to find
the applicable digit map and indicating the
error to return if the parameter is missing.

E.6.5 IG0601 Further modified procedural text.

E.7.3 IG1100 Corrected text identifier for payphone
recognition tone to avoid clash with base
package.

E.10.5 IGDUB Provided informative references for tones and
procedures for continuity check.

E.13 GEN0202 Added note that TDM package could also apply
to other transports.

E.13.1 IG1100 Changed default for echo cancellation from
"on" to provisioned.

E.13.1 IG0601 Corrected type for gain property.

Appendix TTPOST Included a number of corrections which were
I not picked up in H.248.1 Amendment 1 but which
do appear in H.248.1 v2.

Intellectual Property Rights

The ITU draws attention to the possibility that the practice or
implementation of this RFCmay involve the use of a claimed
Intellectual Property Right. The ITU takes no position concerning
the evidence, validity or applicability of claimed Intellectual
Property Rights, whether asserted by ITU members or others outside of
the Recommendation development process.

As of the date of approval of this RFC, the ITU had received notice
of intellectual property, protected by patents, which may be required
to implement this RFC. However, implementors are cautioned that this
may not represent the latest information and are therefore strongly
urged to consult the TSB patent database.

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

Acknowledgments

Megaco/H.248.1 is the result of hard work by many people in both the
IETF and in ITU-T Study Group 16. This section records those who
played a prominent role in ITU-T meetings, on the Megaco list, or
both.

Megaco/H.248 owes a large initial debt to the MGCP protocol (RFC
2705), and thus to its authors, Mauricio Arango, Andrew Dugan, Ike
Elliott, Christian Huitema, and Scott Pickett. Flemming Andreasen
does not appear on this list of authors, but was a major contributor
to the development of both MGCP and Megaco/H.248.1. RFC3435 has an
extensive acknowledgement of many other people who worked on media
gateway control before Megaco got started.

The authors of the first Megaco RFCs (2805, then 3015) were Fernando
Cuervo, Nancy Greene, Abdallah Rayhan, Christian Huitema, Brian
Rosen, and John Segers. Christian Groves conceived and was editor of
Annex C. The people most active on the Megaco list in the period
leading up to the completion of RFC2885 were Brian Rosen, Tom
Taylor, Nancy Greene, Christian Huitema, Matt Holdrege, Chip Sharp,
John Segers, Michael Thomas, Henry Sinnreich, and Paul Sijben. The
people who sacrificed sleep and meals to complete the massive amount
of work required in the decisive Study Group 16 meeting of February,
2000, were Michael Brown, Ranga Dendi, Larry Forni, Glen Freundlich,
Christian Groves, Alf Heidemark, Steve Magnell, Selvam Rengasami,
Rich Rubin, Klaus Sambor, John Segers, Chip Sharp, Tom Taylor, and
Stephen Terrill.

The most active people on the Megaco list in the period since the
February 2000 have been Tom Taylor, Brian Rosen, Christian Groves,
Madhu Babu Brahmanapally, Troy Cauble, Terry Anderson, Chuong Nguyen,
and Kevin Boyle, but many other people have been regular
contributors. Brian Rosen did tremendous service in putting together
the Megaco interoperability tests. On the Study Group 16 side, the
editorial team for the final revised document in February, 2002
included Christian Groves, Marcello Pantaleo, Terry Anderson, Peter
Leis, Kevin Boyle, and Tom Taylor.

Tom Taylor as Megaco Chair managed the day to day operation of the
Megaco list, with Brian Rosen taking an equal share of the burden for
most of the last three years. Glen Freundlich as the Study Group 16
Rapporteur ran the ITU-T meetings and ensured that all of the work at
hand was completed. Without Glen's determination the Megaco/H.248

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

Authors' Addresses

Terry L. Anderson
24 Hill St
Bernardsville, NJ 07924
USA

EMail: tlatla@verizon.net

Christian Groves
Ericsson AsiaPacificLab Australia
37/360 Elizabeth St
Melbourne, Victoria 3000
Australia

EMail: Christian.Groves@ericsson.com.au

Marcello Pantaleo
Ericsson Eurolab Deuschland
Ericsson Allee 1
52134 Herzogenrath, Germany

EMail: Marcello.Pantaleo@eed.ericsson.se

Tom Taylor
Nortel Networks
1852 Lorraine Ave,
Ottawa, Ontario
Canada K1H 6Z8

Phone: +1 613 736 0961
EMail: taylor@nortelnetworks.com

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