Network Working Group F. Cuervo
Request for Comments: 2885 N. Greene
Category: Standards Track Nortel Networks
C. Huitema
Microsoft Corporation
A. Rayhan
Nortel Networks
B. Rosen
Marconi
J. Segers
Lucent Technologies
August 2000
Megaco Protocol version 0.8
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document is common text with Recommendation H.248 as
redetermined in Geneva, February 2000. It must be read in
conjunction with the Megaco Errata, RFC 2886. A merged document
presenting the Megaco protocol with the Errata incorporated will be
available shortly.
The protocol presented in this document meets the requirements for a
media gateway control protocol as presented in RFC 2805.
Cuervo, et al. Standards Track [Page 1]
RFC 2885 Megaco Protocol August 2000
TABLE OF CONTENTS
1. SCOPE..........................................................62. REFERENCES.....................................................62.1 Normative references..........................................62.2 Informative references........................................83. DEFINITIONS....................................................94. ABBREVIATIONS.................................................105. CONVENTIONS...................................................116. CONNECTION MODEL..............................................116.1 Contexts.....................................................146.1.1 Context Attributes and Descriptors....................156.1.2 Creating, Deleting and Modifying Contexts.............156.2 Terminations.................................................156.2.1 Termination Dynamics..................................166.2.2 TerminationIDs........................................176.2.3 Packages..............................................176.2.4 Termination Properties and Descriptors................186.2.5 Root Termination......................................207. COMMANDS......................................................207.1 Descriptors..................................................217.1.1 Specifying Parameters.................................217.1.2 Modem Descriptor......................................227.1.3 Multiplex Descriptor..................................227.1.4 Media Descriptor......................................237.1.5 Termination State Descriptor..........................237.1.6 Stream Descriptor.....................................247.1.7 LocalControl Descriptor...............................247.1.8 Local and Remote Descriptors..........................257.1.9 Events Descriptor.....................................287.1.10 EventBuffer Descriptor...............................317.1.11 Signals Descriptor...................................317.1.12 Audit Descriptor.....................................327.1.13 ServiceChange Descriptor.............................337.1.14 DigitMap Descriptor..................................337.1.15 Statistics Descriptor................................387.1.16 Packages Descriptor..................................397.1.17 ObservedEvents Descriptor............................397.1.18 Topology Descriptor.................................397.2 Command Application Programming Interface....................427.2.1 Add...................................................437.2.2 Modify................................................447.2.3 Subtract..............................................457.2.4 Move..................................................467.2.5 AuditValue............................................477.2.6 AuditCapabilities.....................................487.2.7 Notify................................................497.2.8 ServiceChange.........................................50
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7.2.9 Manipulating and Auditing Context Attributes..........547.2.10 Generic Command Syntax...............................547.3 Command Error Codes..........................................558. TRANSACTIONS..................................................568.1 Common Parameters............................................588.1.1 Transaction Identifiers...............................588.1.2 Context Identifiers...................................588.2 Transaction Application Programming Interface................588.2.1 TransactionRequest....................................598.2.2 TransactionReply......................................598.2.3 TransactionPending....................................608.3 Messages.....................................................619. TRANSPORT.....................................................619.1 Ordering of Commands.........................................629.2 Protection against Restart Avalanche.........................6310. SECURITY CONSIDERATIONS......................................6410.1 Protection of Protocol Connections..........................6410.2 Interim AH scheme...........................................6510.3 Protection of Media Connections.............................6611. MG-MGC CONTROL INTERFACE....................................6611.1 Multiple Virtual MGs........................................6711.2 Cold Start..................................................6811.3 Negotiation of Protocol Version.............................6811.4 Failure of an MG............................................6911.5 Failure of an MGC...........................................6912. PACKAGE DEFINITION...........................................7012.1 Guidelines for defining packages............................7112.1.1 Package..............................................7112.1.2 Properties...........................................7212.1.3 Events...............................................7212.1.4 Signals..............................................7312.1.5 Statistics...........................................7312.1.6 Procedures...........................................7312.2 Guidelines to defining Properties, Statistics and Parameters
to Events and Signals.......................................7312.3 Lists.......................................................7412.4 Identifiers.................................................7412.5 Package Registration........................................7413. IANA CONSIDERATIONS.........................................7413.1 Packages....................................................7413.2 Error Codes.................................................7513.3 ServiceChange Reasons.......................................76
ANNEX A: BINARY ENCODING OF THE PROTOCOL (NORMATIVE).............77A.1 Coding of wildcards..........................................77A.2 ASN.1 syntax specification...................................78A.3 Digit maps and path names....................................94
ANNEX B TEXT ENCODING OF THE PROTOCOL (NORMATIVE)................95B.1 Coding of wildcards..........................................95
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RFC 2885 Megaco Protocol August 2000
B.2 ABNF specification...........................................95
ANNEX C TAGS FOR MEDIA STREAM PROPERTIES (NORMATIVE)............107C.1 General Media Attributes....................................107C.2 Mux Properties..............................................108C.3 General bearer properties...................................109C.4 General ATM properties......................................109C.5 Frame Relay.................................................112C.6 IP..........................................................113C.7 ATM AAL2....................................................113C.8 ATM AAL1....................................................114C.9 Bearer Capabilities.........................................116C.10 AAL5 Properties............................................123C.11 SDP Equivalents............................................124C.12 H.245......................................................124
ANNEX D TRANSPORT OVER IP (NORMATIVE)...........................125D.1 Transport over IP/UDP using Application Level Framing.......125D.1.1 Providing At-Most-Once Functionality.................125D.1.2 Transaction identifiers and three-way handshake......126D.1.2.1 Transaction identifiers....................126D.1.2.2 Three-way handshake........................126D.1.3 Computing retransmission timers......................127D.1.4 Provisional responses................................128D.1.5 Repeating Requests, Responses and Acknowledgements...128
D.2 using TCP..................................................130D.2.1 Providing the At-Most-Once functionality..........130D.2.2 Transaction identifiers and three way handshake...130
D.2.3 Computing retransmission timers...................131D.2.4 Provisional responses.............................131D.2.5 Ordering of commands..............................131
ANNEX E BASIC PACKAGES..........................................131E.1 Generic.....................................................131E.1.1 Properties...........................................132E.1.2 Events...............................................132E.1.3 Signals..............................................133E.1.4 Statistics...........................................133E.2 Base Root Package...........................................133E.2.1 Properties...........................................134E.2.2 Events...............................................135E.2.3 Signals..............................................135E.2.4 Statistics...........................................135E.2.5 Procedures...........................................135E.3 Tone Generator Package......................................135E.3.1 Properties...........................................135E.3.2 Events...............................................136E.3.3 Signals..............................................136E.3.4 Statistics...........................................136E.3.5 Procedures...........................................136E.4 Tone Detection Package......................................137
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E.4.1 Properties...........................................137E.4.2 Events...............................................137E.4.3 Signals..............................................139E.4.4 Statistics...........................................139E.4.5 Procedures...........................................139E.5 Basic DTMF Generator Package................................140E.5.1 Properties...........................................140E.5.2 Events...............................................140E.5.3 Signals..............................................140E.5.4 Statistics...........................................141E.5.5 Procedures...........................................141E.6 DTMF detection Package......................................141E.6.1 Properties...........................................142E.6.2 Events...............................................142E.6.3 Signals..............................................143E.6.4 Statistics...........................................143E.6.5 Procedures...........................................143E.7 Call Progress Tones Generator Package.......................143E.7.1 Properties...........................................144E.7.2 Events...............................................144E.7.3 Signals..............................................144E.7.4 Statistics...........................................145E.7.5 Procedures...........................................145E.8 Call Progress Tones Detection Package.......................145E.8.1 Properties...........................................145E.8.2 Events...............................................145E.8.3 Signals..............................................145E.8.4 Statistics...........................................145E.8.5 Procedures...........................................146E.9 Analog Line Supervision Package.............................146E.9.1 Properties...........................................146E.9.2 Events...............................................146E.9.3 Signals..............................................147E.9.4 Statistics...........................................148E.9.5 Procedures...........................................148E.10 Basic Continuity Package...................................148E.10.1 Properties..........................................148E.10.2 Events..............................................148E.10.3 Signals.............................................149E.10.4 Statistics..........................................150E.10.5 Procedures..........................................150E.11 Network Package............................................150E.11.1 Properties..........................................150E.11.2 Events..............................................151E.11.3 Signals.............................................152E.11.4 Statistics..........................................152E.11.5 Procedures..........................................153E.12 RTP Package...............................................153
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E.12.1 Properties..........................................153E.12.2 Events..............................................153E.12.3 Signals.............................................153E.12.4 Statistics..........................................153E.12.5 Procedures..........................................154E.13 TDM Circuit Package........................................154E.13.1 Properties..........................................155E.13.2 Events..............................................155E.13.3 Signals.............................................155E.13.4 Statistics..........................................156E.13.5 Procedures..........................................156
APPENDIX A EXAMPLE CALL FLOWS (INFORMATIVE).....................157A.1 Residential Gateway to Residential Gateway Call.............157A.1.1 Programming Residential GW Analog Line Terminations for
Idle Behavior..............................................157A.1.2 Collecting Originator Digits and Initiating Termination
...........................................................159
Authors' Addresses..............................................168
Full Copyright Statement........................................170
This document defines the protocol used between elements of a
physically decomposed multimedia gateway. There are no functional
differences from a system view between a decomposed gateway, with
distributed sub-components potentially on more than one physical
device, and a monolithic gateway such as described in H.246. This
recommendation does not define how gateways, multipoint control units
or integrated voice response units (IVRs) work. Instead it creates a
general framework that is suitable for these applications. Packet
network interfaces may include IP, ATM or possibly others. The
interfaces will support a variety of SCN signalling systems,
including tone signalling, ISDN, ISUP, QSIG, and GSM. National
variants of these signalling systems will be supported where
applicable.
The protocol definition in this document is common text with ITU-T
Recommendation H.248. It meets the requirements documented in RFC
2805.
ITU-T Recommendation H.225.0 (1998): "Call Signalling Protocols and
Media Stream Packetization for Packet Based Multimedia Communications
Systems".
Cuervo, et al. Standards Track [Page 6]
RFC 2885 Megaco Protocol August 2000
ITU-T Recommendation H.235 (02/98): "Security and encryption for
H-Series (H.323 and other H.245-based) multimedia terminals".
ITU-T Recommendation H.245 (1998): "Control Protocol for Multimedia
Communication".
ITU-T Recommendation H.323 (1998): "Packet Based Multimedia
Communication Systems".
ITU-T Recommendation I.363.1 (08/96), "B-ISDN ATM Adaptation Layer
specification: Type 1 AAL".
ITU-T Recommendation I.363.2 (09/97), "B-ISDN ATM Adaptation Layer
specification: Type 2 AAL".
ITU-T Recommendation I.363.5 (08/96), "B-ISDN ATM Adaptation Layer
specification: Type 5 AAL".
ITU-T Recommendation I.366.1 (06/98), "Segmentation and Reassembly
Service Specific Convergence Sublayer for the AAL type 2".
ITU-T Recommendation I.366.2 (02/99), "AAL type 2 service specific
convergence sublayer for trunking".
ITU-T Recommendation I.371 (08/96), "Traffic control and congestion
control in B-ISDN".
ITU-T Recommendation Q.763 (09/97), "Signalling System No. 7 - ISDN
user part formats and codes".
ITU-T Recommendation Q.765, "Signalling System No. 7 - Application
transport mechanism".
ITU-T Recommendation Q.931 (05/98): "Digital Subscriber Signalling
System No. 1 (DSS 1) - ISDN User-Network Interface Layer 3
Specification for Basic Call Control".
ITU-T Recommendation Q.2630.1 (1999), "AAL Type 2 Signalling Protocol
(Capability Set 1)".
ITU-T Recommendation Q.2931 (10/95), "Broadband Integrated Services
Digital Network (B-ISDN) - Digital Subscriber Signalling System No.
2 (DSS 2) - User-Network Interface (UNI) - Layer 3 specification for
basic call/connection control".
ITU-T Recommendation Q.2941.1 (09/97), "Digital Subscriber Signalling
System No. 2 - Generic Identifier Transport".
Cuervo, et al. Standards Track [Page 7]
RFC 2885 Megaco Protocol August 2000
ITU-T Recommendation Q.2961 (10/95), "Broadband integrated services
digital network (B-ISDN) - Digital subscriber signalling system no.2
(DSS 2) - additional traffic parameters".
ITU-T Recommendation Q.2961.2 (06/97), "Digital subscriber signalling
system No. 2 - Additional traffic parameters: Support of ATM transfer
capability in the broadband bearer capability information element."
ITU-T Recommendation X.213 (11/1995), "Information technology - Open
System Interconnection - Network service definition plus Amendment 1
(08/1997), Addition of the Internet protocol address format
identifier".
ITU-T Recommendation V.76 (08/96), "Generic multiplexer using V.42
LAPM-based procedures".
ITU-T Recommendation X.680 (1997): "Information technology-Abstract
Syntax Notation One (ASN.1): Specification of basic notation".
ITU-T Recommendation H.246 (1998), "Interworking of H-series
multimedia terminals with H-series multimedia terminals and
voice/voiceband terminals on GSTN and ISDN".
Rose, M. and D. Cass, "ISO Transport Service on top of the TCP,
Version 3", RFC 1006, May 1987.
Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, November 1997.
Handley, M. and V. Jacobson, "SDP: Session Description Protocol",
RFC 2327, April 1998.
Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
Kent, S. and R. Atkinson, "IP Encapsulating Security Payload (ESP)",
RFC 2406, November 1998.
ITU-T Recommendation E.180/Q.35 (1998): "Technical characteristics of
tones for the telephone service".
CCITT Recommendation G.711 (1988), "Pulse Code Modulation (PCM) of
voice frequencies".
ITU-T Recommendation H.221 (05/99),"Frame structure for a 64 to 1920
kbit/s channel in audiovisual teleservices".
Cuervo, et al. Standards Track [Page 8]
RFC 2885 Megaco Protocol August 2000
ITU-T Recommendation H.223 (1996), "Multiplexing protocol for low bit
rate multimedia communication".
ITU-T Recommendation Q.724 (1988): "Signalling procedures".
Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980.
Postel, J., "Internet protocol", STD 5, RFC 791, September 1981.
Postel, J., "TRANSMISSION CONTROL PROTOCOL", STD 7, RFC 793,
September 1981.
Simpson, W., "The Point-to-Point Protocol", STD 51, RFC 1661, July
1994.
Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A
Transport Protocol for Real-Time Applications", RFC 1889, January
1996.
Schulzrinne, H., "RTP Profile for Audio and Video Conferences with
Minimal Control", RFC 1890, January 1996.
Kent, S. and R. Atkinson, "Security Architecture for the Internet
Protocol", RFC 2401, November 1998.
Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg, "SIP:
Session Initiation Protocol", RFC 2543, March 1999.
Greene, N., Ramalho, M. and B. Rosen, "Media Gateway control protocol
architecture and requirements", RFC 2805, April 1999.
Access Gateway: A type of gateway that provides a User to Network
Interface (UNI) such as ISDN.
Descriptor: A syntactic element of the protocol that groups related
properties. For instance, the properties of a media flow on the MG
can be set by the MGC by including the appropriate descriptor in a
command.
Media Gateway (MG): The media gateway converts media provided in one
type of network to the format required in another type of network.
For example, a MG could terminate bearer channels from a switched
circuit network (e.g., DS0s) and media streams from a packet network
Cuervo, et al. Standards Track [Page 9]
RFC 2885 Megaco Protocol August 2000
(e.g., RTP streams in an IP network). This gateway may be capable of
processing audio, video and T.120 alone or in any combination, and
will be capable of full duplex media translations. The MG may also
play audio/video messages and performs other IVR functions, or may
perform media conferencing.
Media Gateway Controller (MGC): Controls the parts of the call state
that pertain to connection control for media channels in a MG.
Multipoint Control Unit (MCU): An entity that controls the setup and
coordination of a multi-user conference that typically includes
processing of audio, video and data.
Residential Gateway: A gateway that interworks an analogue line to a
packet network. A residential gateway typically contains one or two
analogue lines and is located at the customer premises.
SCN FAS Signalling Gateway: This function contains the SCN Signalling
Interface that terminates SS7, ISDN or other signalling links where
the call control channel and bearer channels are collocated in the
same physical span.
SCN NFAS Signalling Gateway: This function contains the SCN
Signalling Interface that terminates SS7 or other signalling links
where the call control channels are separated from bearer channels.
Stream: Bidirectional media or control flow received/sent by a media
gateway as part of a call or conference.
Trunk: A communication channel between two switching systems such as
a DS0 on a T1 or E1 line.
Trunking Gateway: A gateway between SCN network and packet network
that typically terminates a large number of digital circuits.
This recommendation defines the following terms.
ATM Asynchronous Transfer Mode
BRI Basic Rate Interface
CAS Channel Associated Signalling
DTMF Dual Tone Multi-Frequency
FAS Facility Associated Signalling
GW GateWay
IANA Internet Assigned Numbers Authority
IP Internet Protocol
ISUP ISDN User Part
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RFC 2885 Megaco Protocol August 2000
MG Media Gateway
MGC Media Gateway Controller
NFAS Non-Facility Associated Signalling
PRI Primary Rate Interface
PSTN Public Switched Telephone Network
QoS Quality of Service
RTP Real-time Transport Protocol
SCN Switched Circuit Network
SG Signalling Gateway
SS7 Signalling System No. 7
In this recommendation, "shall" refers to a mandatory requirement,
while "should" refers to a suggested but optional feature or
procedure. The term "may" refers to an optional course of action
without expressing a preference.
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.
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RFC 2885 Megaco Protocol August 2000
The maximum number of Terminations in a Context is a MG property.
Media gateways that offer only point-to-point connectivity might
allow at most two Terminations per Context. Media gateways that
support multipoint conferences might allow three or more terminations
per Context.
The attributes of Contexts are:
. ContextID.
. The topology (who hears/sees whom). The topology of a Context
describes the flow of media between the Terminations within a
Context. In contrast, the mode of a Termination (send/receive/_)
describes the flow of the media at the ingress/egress of the
media gateway.
. The priority is used for a context in order to provide the MG
with information about a certain precedence handling for a
context. The MGC can also use the priority to control
autonomously the traffic precedence in the MG in a smooth way in
certain situations (e.g. restart), when a lot of contexts must
be handled simultaneously.
. An indicator for an emergency call is also provided to allow a
preference handling in the MG.
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.
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.
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RFC 2885 Megaco Protocol August 2000
Terminations representing ephemeral information flows, such as RTP
flows, would usually exist only for the duration of their use.
Ephemeral Terminations are created by means of an Add command. They
are destroyed by means of a Subtract command. In contrast, when a
physical Termination is Added to or Subtracted from a Context, it is
taken from or to the null Context, respectively.
Terminations may have signals applied to them. Signals are MG
generated media streams such as tones and announcements as well as
line signals such as hookswitch. Terminations may be programmed to
detect Events, the occurrence of which can trigger notification
messages to the MGC, or action by the MG. Statistics may be
accumulated on a Termination. Statistics are reported to the MGC
upon request (by means of the AuditValue command, see section 7.2.5)
and when the Termination is taken out of the call it is in.
Multimedia gateways may process multiplexed media streams. For
example, Recommendation H.221 describes a frame structure for
multiple media streams multiplexed on a number of digital 64 kbit/s
channels. Such a case is handled in the connection model in the
following way. For every bearer channel that carries part of the
multiplexed streams, there is a Termination. The Terminations that
source/sink the digital channels are connected to a separate
Termination called the multiplexing Termination. This Termination
describes the multiplex used (e.g. how the H.221 frames are carried
over the digital channels used). The MuxDescriptor is used to this
end. If multiple media are carried, this Termination contains
multiple StreamDescriptors. The media streams can be associated with
streams sourced/sunk by other Terminations in the Context.
Terminations may be created which represent multiplexed bearers, such
as an ATM AAL2. When a new multiplexed bearer is to be created, an
ephemeral termination is created in a context established for this
purpose. When the termination is subtracted, the multiplexed bearer
is destroyed.
The protocol can be used to create new Terminations and to modify
property values of existing Terminations. These modifications
include the possibility of adding or removing events and/or signals.
The Termination properties, and events and signals are described in
the ensuing sections. An MGC can only release/modify terminations and
the resources that the termination represents which it has previously
seized via, e.g., the Add command.
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RFC 2885 Megaco Protocol August 2000
Terminations are referenced by a TerminationID, which is an arbitrary
schema chosen by the MG.
TerminationIDs of physical Terminations are provisioned in the Media
Gateway. The TerminationIDs may be chosen to have structure. For
instance, a TerminationID may consist of trunk group and a trunk
within the group.
A wildcarding mechanism using two types of wildcards can be used with
TerminationIDs. The two wildcards are ALL and CHOOSE. The former is
used to address multiple Terminations at once, while the latter is
used to indicate to a media gateway that it must select a Termination
satisfying the partially specified TerminationID. This allows, for
instance, that a MGC instructs a MG to choose a circuit within a
trunk group.
When ALL is used in the TerminationID of a command, the effect is
identical to repeating the command with each of the matching
TerminationIDs. Since each of these commands may generate a
response, the size of the entire response may be large. If
individual responses are not required, a wildcard response may be
requested. In such a case, a single response is generated, which
contains the UNION of all of the individual responses which otherwise
would have been generated, with duplicate values suppressed.
Wildcard response may be particularly useful in the Audit commands.
The encoding of the wildcarding mechanism is detailed in Annexes A
and B.
Different types of gateways may implement Terminations that have
widely differing characteristics. Variations in Terminations are
accommodated in the protocol by allowing Terminations to have
optional Properties, Events, Signals and Statistics implemented by
MGs.
In order to achieve MG/MGC interoperability, such options are grouped
into Packages, and a Termination realizes a set of such Packages.
More information on definition of packages can be found in section
12. An MGC can audit a Termination to determine which Packages it
realizes.
Properties, Events, Signals and Statistics defined in Packages, as
well as parameters to them, are referenced by identifiers (Ids).
Identifiers are scoped. For each package, PropertyIds, EventIds,
Cuervo, et al. Standards Track [Page 17]
RFC 2885 Megaco Protocol August 2000
SignalIds, StatisticsIds and ParameterIds have unique name spaces and
the same identifier may be used in each of them. Two PropertyIds in
different packages may also have the same identifier, etc.
Terminations have properties. The properties have unique
PropertyIDs. Most properties have default values. When a
Termination is created, properties get their default values, unless
the controller specifically sets a different value. The default
value of a property of a physical Termination can be changed by
setting it to a different value when the Termination is in the null
Context. Every time such a Termination returns to the null Context,
the values of its properties are reset to this default value.
There are a number of common properties for Terminations and
properties specific to media streams. The common properties are also
called the termination state properties. For each media stream,
there are local properties and properties of the received and
transmitted flows.
Properties not included in the base protocol are defined in Packages.
These properties are referred to by a name consisting of the
PackageName and a PropertyId. Most properties have default values
described in the Package description. Properties may be read- only or
read/write. The possible values of a property may be audited, as can
their current values. For properties that are read/write, the MGC
can set their values. A property may be declared as "Global" which
has a single value shared by all terminations realizing the package.
Related properties are grouped into descriptors for convenience.
When a Termination is Added to a Context, the value of its read/write
properties can be set by including the appropriate descriptors as
parameters to the Add command. Properties not mentioned in the
command retain their prior values. Similarly, a property of a
Termination in a Context may have its value changed by the Modify
command. Properties not mentioned in the Modify command retain their
prior values. Properties may also have their values changed when a
Termination is moved from one Context to another as a result of a
Move command. In some cases, descriptors are returned as output from
a command.
The following table lists all of the possible Descriptors and their
use. Not all descriptors are legal as input or output parameters to
every command.
Cuervo, et al. Standards Track [Page 18]
RFC 2885 Megaco Protocol August 2000
Descriptor Name Description
Modem Identifies modem type and properties when
applicable.
Mux Describes multiplex type for multimedia
terminations (e.g. H.221, H.223, H.225.0)
and Terminations forming the input mux.
Media A list of media stream specifications (see
7.1.4).
TerminationState Properties of a Termination (which can be
defined in Packages) that are not stream
specific.
Stream A list of remote/local/localControl
descriptors for a single stream.
Local Contains properties that specify the media
flows that the MG receives from the remote
entity.
Remote Contains properties that specify the media
flows that the MG sends to the remote
entity.
LocalControl Contains properties (which can be defined
in packages) that are of interest between
the MG and the MGC.
Events Describes events to be detected by the MG
and what to do when an event is detected.
EventBuffer Describes events to be detected by the MG
when Event Buffering is active.
Signals Describes signals and/or actions to be
applied (e.g. Busy Tone) to the
Terminations.
Audit In Audit commands, identifies which
information is desired.
Packages In AuditValue, returns a list of Packages
realized by Termination.
DigitMap Instructions for handling DTMF tones at
the MG.
ServiceChange In ServiceChange, what, why service change
occurred, etc.
ObservedEvents In Notify or AuditValue, report of events
observed.
Statistics In Subtract and Audit, Report of
Statistics kept on a Termination.
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Occasionally, a command must refer to the entire gateway, rather than
a termination within it. A special TerminationID, "Root" is reserved
for this purpose. Packages may be defined on Root. Root thus may
have properties and events (signals are not appropriate for root).
Accordingly, the root TerminationID may appear in:
. a Modify command - to change a property or set an event
. a Notify command - to report an event
. an AuditValue return - to examine the values of properties
implemented on root
. an AuditCapability - to determine what properties of root are
implemented
. a ServiceChange - to declare the gateway in or out of service.
Any other use of the root TerminationID is an error.
The protocol provides commands for manipulating the logical entities
of the protocol connection model, Contexts and Terminations.
Commands provide control at the finest level of granularity supported
by the protocol. For example, Commands exist to add Terminations to
a Context, modify Terminations, subtract Terminations from a Context,
and audit properties of Contexts or Terminations. Commands provide
for complete control of the properties of Contexts and Terminations.
This includes specifying which events a Termination is to report,
which signals/actions are to be applied to a Termination and
specifying the topology of a Context (who hears/sees whom).
Most commands are for the specific use of the Media Gateway
Controller as command initiator in controlling Media Gateways as
command responders. The exceptions are the Notify and ServiceChange
commands: Notify is sent from Media Gateway to Media Gateway
Controller, and ServiceChange may be sent by either entity. Below is
an overview of the commands; they are explained in more detail in
section 7.2.
1. Add. The Add command adds a termination to a context. The Add
command on the first Termination in a Context is used to create a
Context.
2. Modify. The Modify command modifies the properties, events and
signals of a termination.
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3. Subtract. The Subtract command disconnects a Termination from its
Context and returns statistics on the Termination's participation
in the Context. The Subtract command on the last Termination in a
Context deletes the Context.
4. Move. The Move command atomically moves a Termination to another
context.
5. AuditValue. The AuditValue command returns the current state of
properties, events, signals and statistics of Terminations.
6. AuditCapabilities. The AuditCapabilities command returns all the
possible values for Termination properties, events and signals
allowed by the Media Gateway.
7. Notify. The Notify command allows the Media Gateway to inform the
Media Gateway Controller of the occurrence of events in the Media
Gateway.
8. ServiceChange. The ServiceChange Command allows the Media Gateway
to notify the Media Gateway Controller that a Termination or group
of Terminations is about to be taken out of service or has just
been returned to service. ServiceChange is also used by the MG
to announce its availability to an MGC (registration), and to
notify the MGC of impending or completed restart of the MG. The
MGC may announce a handover to the MG by sending it a
ServiceChange command. The MGC may also use ServiceChange to
instruct the MG to take a Termination or group of Terminations in
or out of service.
These commands are detailed in sections 7.2.1 through 7.2.8
The parameters to a command are termed Descriptors. A Descriptor
consists of a name and a list of items. Some items may have values.
Many Commands share common Descriptors. This subsection enumerates
these Descriptors. Descriptors may be returned as output from a
command. Parameters and parameter usage specific to a given Command
type are described in the subsection that describes the Command.
Command parameters are structured into a number of descriptors. In
general, the text format of descriptors is
DescriptorName=<someID>{parm=value, parm=value_.}.
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Parameters may be fully specified, over-specified or under-specified:
1. Fully specified parameters have a single, unambiguous value that
the command initiator is instructing the command responder to use
for the specified parameter.
2. Under-specified parameters, using the CHOOSE value, allow the
command responder to choose any value it can support.
3. Over-specified parameters have a list of potential values. The
list order specifies the command initiator's order of preference
of selection. The command responder chooses one value from the
offered list and returns that value to the command initiator.
Unspecified mandatory parameters (i.e. mandatory parameters not
specified in a descriptor) result in the command responder retaining
the previous value for that parameter. Unspecified optional
parameters result in the command responder using the default value of
the parameter. Whenever a parameter is underspecified or
overspecified, the descriptor containing the value chosen by the
responder is included as output from the command.
Each command specifies the TerminationId the command operates on.
This TerminationId may be "wildcarded". When the TerminationId of a
command is wildcarded, the effect shall be as if the command was
repeated with each of the TerminationIds matched.
The Modem descriptor specifies the modem type and parameters, if any,
required for use in e.g. H.324 and text conversation. The descriptor
includes the following modem types: V.18, V.22, V.22bis, V.32,
V.32bis, V.34, V.90, V.91, Synchronous ISDN, and allows for
extensions. By default, no modem descriptor is present in a
Termination.
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
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and a set of TerminationIDs representing the multiplexed inputs, in
order. For example:
Mux = H.221{ MyT3/1/2, MyT3/2/13, MyT3/3/6, MyT3/21/22}
The Media Descriptor specifies the parameters for all the media
streams. These parameters are structured into two descriptors, a
Termination State Descriptor, which specifies the properties of a
termination that are not stream dependent, and one or more Stream
Descriptors each of which describes a single media stream.
A stream is identified by a StreamID. The StreamID is used to link
the streams in a Context that belong together. Multiple streams
exiting a termination shall be synchronized with each other. Within
the Stream Descriptor, there are up to three subsidiary descriptors,
LocalControl, Local, and Remote. The relationship between these
descriptors is thus:
Media Descriptor
TerminationStateDescriptor
Stream Descriptor
LocalControl Descriptor
Local Descriptor
Remote Descriptor
As a convenience a LocalControl, Local, or Remote descriptor may be
included in the Media Descriptor without an enclosing Stream
descriptor. In this case, the StreamID is assumed to be 1.
The Termination State Descriptor contains the ServiceStates property,
the EventBufferControl property and properties of a termination
(defined in Packages) that are not stream specific.
The ServiceStates property describes the overall state of the
termination (not stream-specific). A Termination can be in one of
the following states: "test", "out of service", or "in service". The
"test" state indicates that the termination is being tested. The
state "out of service" indicates that the termination cannot be used
for traffic. The state "in service" indicates that a termination can
be used or is being used for normal traffic. "in service" is the
default state.
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Values assigned to Properties may be simple values
(integer/string/enumeration) or may be underspecified, where more
than one value is supplied and the MG may make a choice:
. Alternative Values: multiple values in a list, one of which must
be selected
. Ranges: minimum and maximum values, any value between min and max
must be selected, boundary values included
. Greater Than/Less Than: value must be greater/less than specified
value
. CHOOSE Wildcard: the MG chooses from the allowed values for the
property
The EventBufferControl property specifies whether events are
buffered following detection of an event in the Events Descriptor, or
processed immediately. See section 7.1.9 for details.
A Stream descriptor specifies the parameters of a single bi-
directional stream. These parameters are structured into three
descriptors: one that contains termination properties specific to a
stream and one each for local and remote flows. The Stream Descriptor
includes a StreamID which identifies the stream. Streams are created
by specifying a new StreamID on one of the terminations in a Context.
A stream is deleted by setting empty Local and Remote descriptors for
the stream with ReserveGroup and ReserveValue in LocalControl set to
"false" on all terminations in the context that previously supported
that stream.
StreamIDs are of local significance between MGC and MG and they are
assigned by the MGC. Within a context, StreamID is a means by which
to indicate which media flows are interconnected: streams with the
same StreamID are connected.
If a termination is moved from one context to another, the effect on
the context to which the termination is moved is the same as in the
case that a new termination were added with the same StreamIDs as the
moved termination.
The LocalControl Descriptor contains the Mode property, the
ReserveGroup and ReserveValue properties and properties of a
termination (defined in Packages) that are stream specific, and are
of interest between the MG and the MGC. Values of properties may be
underspecified as in section 7.1.1.
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The allowed values for the mode property are send-only, receive-only,
send/receive, inactive and loop-back. "Send" and "receive" are with
respect to the exterior of the context, so that, for example, a
stream set to mode=sendonly does not pass received media into the
context. Signals and Events are not affected by mode.
The boolean-valued Reserve properties, ReserveValue and ReserveGroup,
of a Termination indicate what the MG is expected to do when it
receives a local and/or remote descriptor.
If the value of a Reserve property is True, the MG SHALL reserve
resources for all alternatives specified in the local and/or remote
descriptors for which it currently has resources available. It SHALL
respond with the alternatives for which it reserves resources. If it
cannot not support any of the alternatives, it SHALL respond with a
reply to the MGC that contains empty local and/or remote descriptors.
If the value of a Reserve property is False, the MG SHALL choose one
of the alternatives specified in the local descriptor (if present)
and one of the alternatives specified in the remote descriptor (if
present). If the MG has not yet reserved resources to support the
selected alternative, it SHALL reserve the resources. If, on the
other hand, it already reserved resources for the Termination
addressed (because of a prior exchange with ReserveValue and/or
ReserveGroup equal to True), it SHALL release any excess resources it
reserved previously. Finally, the MG shall send a reply to the MGC
containing the alternatives for the local and/or remote descriptor
that it selected. If the MG does not have sufficient resources to
support any of the alternatives specified, is SHALL respond with
error 510 (insufficient resources).
The default value of ReserveValue and ReserveGroup is False.
A new setting of the LocalControl Descriptor completely replaces the
previous setting of that descriptor in the MG. Thus to retain
information from the previous setting the MGC must include that
information in the new setting. If the MGC wishes to delete some
information from the existing descriptor, it merely resends the
descriptor (in a Modify command) with the unwanted information
stripped out.
The MGC uses Local and Remote descriptors to reserve and commit MG
resources for media decoding and encoding for the given Stream(s) and
Termination to which they apply. The MG includes these descriptors
in its response to indicate what it is actually prepared to support.
The MG SHALL include additional properties and their values in its
Cuervo, et al. Standards Track [Page 25]
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response if these properties are mandatory yet not present in the
requests made by the MGC (e.g., by specifying detailed video encoding
parameters where the MGC only specified the payload type).
Local refers to the media received by the MG and Remote refers to the
media sent by the MG.
When text encoding the protocol, the descriptors consist of session
descriptions as defined in SDP (RFC2327). In session descriptions
sent from the MGC to the MG, the following exceptions to the syntax
of RFC 2327 are allowed:
. the "s=", "t=" and "o=" lines are optional,
. the use of CHOOSE is allowed in place of a single parameter
value, and
. the use of alternatives is allowed in place of a single parameter
value.
When multiple session descriptions are provided in one descriptor,
the "v=" lines are required as delimiters; otherwise they are
optional in session descriptions sent to the MG. Implementations
shall accept session descriptions that are fully conformant to
RFC2327. When binary encoding the protocol the descriptor consists of
groups of properties (tag-value pairs) as specified in Annex C. Each
such group may contain the parameters of a session description.
Below, the semantics of the local and remote descriptors are
specified in detail. The specification consists of two parts. The
first part specifies the interpretation of the contents of the
descriptor. The second part specifies the actions the MG must take
upon receiving the local and remote descriptors. The actions to be
taken by the MG depend on the values of the ReserveValue and
ReserveGroup properties of the LocalControl descriptor.
Either the local or the remote descriptor or both may be
. unspecified (i.e., absent),
. empty,
. underspecified through use of CHOOSE in a property value,
. fully specified, or
. overspecified through presentation of multiple groups of
properties and possibly multiple property values in one or more
of these groups.
Where the descriptors have been passed from the MGC to the MG, they
are interpreted according to the rules given in section 7.1.1, with
the following additional comments for clarification:
Cuervo, et al. Standards Track [Page 26]
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(a) An unspecified Local or Remote descriptor is considered to be a
missing mandatory parameter. It requires the MG to use whatever was
last specified for that descriptor. It is possible that there was no
previously-specified value, in which case the descriptor concerned is
ignored in further processing of the command.
(b) An empty Local (Remote) descriptor in a message from the MGC
signifies a request to release any resources reserved for the media
flow received (sent).
(c) If multiple groups of properties are present in a Local or Remote
descriptor or multiple values within a group, the order of preference
is descending.
(d) Underspecified or overspecified properties within a group of
properties sent by the MGC are requests for the MG to choose one or
more values which it can support for each of those properties. In
case of an overspecified property, the list of values is in
descending order of preference.
Subject to the above rules, subsequent action depends on the values
of the ReserveValue and ReserveGroup properties in LocalControl.
If ReserveGroup is true, the MG reserves the resources required to
support any of the requested property group alternatives that it can
currently support. If ReserveValue is true, the MG reserves the
resources required to support any of the requested property value
alternatives that it can currently support.
NOTE - If a Local or Remote descriptor contains multiple groups of
properties, and ReserveGroup is true, then the MG is requested to
reserve resources so that it can decode or encode the media stream
according to any of the alternatives. For instance, if the Local
descriptor contains two groups of properties, one specifying
packetized G.711 A-law audio and the other G.723.1 audio, the MG
reserves resources so that it can decode one audio stream encoded in
either G.711 A-law format or G.723.1 format. The MG does not have to
reserve resources to decode two audio streams simultaneously, one
encoded in G.711 A-law and one in G.723.1. The intention for the use
of ReserveValue is analogous.
If ReserveGroup is true or ReserveValue is true, then the following
rules apply.
. If the MG has insufficient resources to support all alternatives
requested by the MGC and the MGC requested resources in both
Local and Remote, the MG should reserve resources to support at
least one alternative each within Local and Remote.
Cuervo, et al. Standards Track [Page 27]
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. If the MG has insufficient resources to support at least one
alternative within a Local (Remote) descriptor received from
the MGC, it shall return an empty Local (Remote) in response.
. In its response to the MGC, when the MGC included Local and
Remote descriptors, the MG SHALL include Local and Remote
descriptors for all groups of properties and property values it
reserved resources for. If the MG is incapable of supporting at
least one of the alternatives within the Local (Remote)
descriptor received from the MGC, it SHALL return an empty Local
(Remote) descriptor.
. If the Mode property of the LocalControl descriptor is RecvOnly
or SendRecv, the MG must be prepared to receive media encoded
according to any of the alternatives included in its response to
the MGC.
. If ReserveGroup is False and ReserveValue is false, then the MG
SHOULD apply the following rules to resolve Local and Remote to a
single alternative each:
. The MG chooses the first alternative in Local for which it is
able to support at least one alternative in Remote.
. If the MG is unable to support at least one Local and one Remote
alternative, it returns Error 510 (Insufficient Resources).
. The MG returns its selected alternative in each of Local and
Remote.
A new setting of a Local or Remote Descriptor completely replaces the
previous setting of that descriptor in the MG. Thus to retain
information from the previous setting the MGC must include that
information in the new setting. If the MGC wishes to delete some
information from the existing descriptor, it merely resends the
descriptor (in a Modify command) with the unwanted information
stripped out.
The EventsDescriptor parameter contains a RequestIdentifier and a
list of events that the Media Gateway is requested to detect and
report. The RequestIdentifier is used to correlate the request with
the notifications that it may trigger. Requested events include, for
example, fax tones, continuity test results, and on-hook and off-hook
transitions.
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Each event in the descriptor contains the Event name, an optional
streamID, an optional KeepActive flag, and optional parameters. The
Event name consists of a Package Name (where the event is defined)
and an EventID. The ALL wildcard may be used for the EventID,
indicating that all events from the specified package have to be
detected. The default streamID is 0, indicating that the event to be
detected is not related to a particular media stream. Events can
have parameters. This allows a single event description to have some
variation in meaning without creating large numbers of individual
events. Further event parameters are defined in the package.
The default action of the MG, when it detects an event in the Events
Descriptor, is to send a Notify command to the MG. Any other action
is for further study.
If the value of the EventBufferControl property equals LockStep,
following detection of such an event, normal handling of events is
suspended. Any event which is subsequently detected and occurs in the
EventBuffer Descriptor is added to the end of the EventBuffer (a FIFO
queue), along with the time that it was detected. The MG SHALL wait
for a new EventsDescriptor to be loaded. A new EventsDescriptor can
be loaded either as the result of receiving a command with a new
EventsDescriptor, or by activating an embedded EventsDescriptor.
If EventBufferControl equals Off, the MG continues processing based
on the active EventsDescriptor.
In the case that an embedded EventsDescriptor being activated, the MG
continues event processing based on the newly activated
EventsDescriptor (Note - for purposes of EventBuffer handling,
activation of an embedded EventsDescriptor is equivalent to receipt
of a new EventsDescriptor).
When the MG receives a command with a new EventsDescriptor, one or
more events may have been buffered in the EventBuffer in the MG. The
value of EventBufferControl then determines how the MG treats such
buffered events.
Case 1
If EventBufferControl = LockStep and the MG receives a new
EventsDescriptor it will check the FIFO EventBuffer and take the
following actions:
1. If the EventBuffer is empty, the MG waits for detection of events
based on the new EventsDescriptor.
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2. If the EventBuffer is non-empty, the MG processes the FIFO queue
starting with the first event:
a) If the event in the queue is in the events listed in the new
EventsDescriptor, the default action of the MG is to send a
Notify command to the MGC and remove the event from the
EventBuffer. Any other action is for further study. The time
stamp of the Notify shall be the time the event was actually
detected. The MG then waits for a new EventsDescriptor. While
waiting for a new EventsDescriptor, any events matching the
EventsBufferDescriptor will be placed in the EventBuffer and
the event processing will repeat from step 1.
b) If the event is not in the new EventsDescriptor, the MG
SHALL discard the event and repeat from step 1.
Case 2
If EventBufferControl equals Off and the MG receives a new
EventsDescriptor, it processes new events with the new
EventsDescriptor.
If the MG receives a command instructing it to set the value of
EventBufferControl to Off, all events in the EventBuffer SHALL be
discarded.
The MG may report several events in a single Transaction as long as
this does not unnecessarily delay the reporting of individual events.
For procedures regarding transmitting the Notify command, refer to
the appropriate annex for specific transport considerations.
The default value of EventBufferControl is Off.
Note - Since the EventBufferControl property is in the
TerminationStateDescriptor, the MG might receive a command that
changes the EventBufferControl property and does not include an
EventsDescriptor.
Normally, detection of an event shall cause any active signals to
stop. When KeepActive is specified in the event, the MG shall not
interrupt any signals active on the Termination on which the event is
detected.
An event can include an Embedded Signals descriptor and/or an
Embedded Events Descriptor which, if present, replaces the current
Signals/Events descriptor when the event is detected. It is
possible, for example, to specify that the dial-tone Signal be
Cuervo, et al. Standards Track [Page 30]
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generated when an off-hook Event is detected, or that the dial-tone
Signal be stopped when a digit is detected. A media gateway
controller shall not send EventsDescriptors with an event both marked
KeepActive and containing an embedded SignalsDescriptor.
Only one level of embedding is permitted. An embedded
EventsDescriptor SHALL NOT contain another embedded EventsDescriptor;
an embedded EventsDescriptor may contain an embedded
SignalsDescriptor.
An EventsDescriptor received by a media gateway replaces any previous
Events Descriptor. Event notification in process shall complete, and
events detected after the command containing the new EventsDescriptor
executes, shall be processed according to the new EventsDescriptor.
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).
A SignalsDescriptor is a parameter that contains the set of signals
that the Media Gateway is asked to apply to a Termination. A
SignalsDescriptor contains a number of signals and/or sequential
signal lists. A SignalsDescriptor may contain zero signals and
sequential signal lists. Support of sequential signal lists is
optional.
Signals are defined in packages. Signals shall be named with a
Package name (in which the signal is defined) and a SignalID. No
wildcard shall be used in the SignalID. Signals that occur in a
SignalsDescriptor have an optional StreamID parameter (default is 0,
to indicate that the signal is not related to a particular media
stream), an optional signal type (see below), an optional duration
and possibly parameters defined in the package that defines the
signal. This allows a single signal to have some variation in
meaning, obviating the need to create large numbers of individual
signals. Finally, the optional parameter "notifyCompletion" allows a
MGC to indicate that it wishes to be notified when the signal
finishes playout. When the MGC enables the signal completion event
(see section E.1.2) in an Events Descriptor, that event is detected
whenever a signal terminates and "notifyCompletion" for that signal
is set to TRUE. The signal completion event of section E.1.2 has a
parameter that indicates how the signal terminated: it played to
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completion, it was interrupted by an event, it was halted because a
new SignalsDescriptor arrived, or the signal did not complete for
some other reason.
The duration is an integer value that is expressed in hundredths of a
second.
There are three types of signals:
. on/off - the signal lasts until it is turned off,
. timeout - the signal lasts until it is turned off or a specific
period of time elapses,
. brief - the signal duration is so short that it will stop on its
own unless a new signal is applied that causes it to stop; no
timeout value is needed.
If the signal type is specified in a SignalsDescriptor, it overrides
the default signal type (see Section 12.1.4). If duration is
specified for an on/off signal, it SHALL be ignored.
A sequential signal list consists of a signal list identifier, a
sequence of signals to be played sequentially, and a signal type.
Only the trailing element of the sequence of signals in a sequential
signal list may be an on/off signal. If the trailing element of the
sequence is an on/off signal, the signal type of the sequential
signal list shall be on/off as well. If the sequence of signals in a
sequential signal list contains signals of type timeout and the
trailing element is not of type on/off, the type of the sequential
signal list SHALL be set to timeout. The duration of a sequential
signal list with type timeout is the sum of the durations of the
signals it contains. If the sequence of signals in a sequential
signal list contains only signals of type brief, the type of the
sequential signal list SHALL be set to brief. A signal list is
treated as a single signal of the specified type when played out.
Multiple signals and sequential signal lists in the same
SignalsDescriptor shall be played simultaneously.
Signals are defined as proceeding from the termination towards the
exterior of the Context unless otherwise specified in a package.
When the same Signal is applied to multiple Terminations within one
Transaction, the MG should consider using the same resource to
generate these Signals.
Production of a Signal on a Termination is stopped by application of
a new SignalsDescriptor, or detection of an Event on the Termination
(see section 7.1.9).
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A new SignalsDescriptor replaces any existing SignalsDescriptor. Any
signals applied to the Termination not in the replacement descriptor
shall be stopped, and new signals are applied, except as follows.
Signals present in the replacement descriptor and containing the
KeepActive flagshall be continued if they are currently playing and
have not already completed. If a replacement signal descriptor
contains a signal that is not currently playing and contains the
KeepActive flag, that signal SHALL be ignored. If the replacement
descriptor contains a sequential signal list with the same identifier
as the existing descriptor, then
. the signal type and sequence of signals in the sequential signal
list in the replacement descriptor shall be ignored, and
. the playing of the signals in the sequential signal list in the
existing descriptor shall not be interrupted.
The Audit Descriptor specifies what information is to be audited.
The Audit Descriptor specifies the list of descriptors to be
returned. Audit may be used in any command to force the return of a
descriptor even if the descriptor in the command was not present, or
had no underspecified parameters. Possible items in the Audit
Descriptor are:
Modem
Mux
Events
Media
Signals
ObservedEvents
DigitMap
Statistics
Packages
EventBuffer
Audit may be empty, in which case, no descriptors are returned. This
is useful in Subtract, to inhibit return of statistics, especially
when using wildcard.
A DigitMap is a dialing plan resident in the Media Gateway used for
detecting and reporting digit events received on a Termination. The
DigitMap Descriptor contains a DigitMap name and the DigitMap to be
assigned. A digit map may be preloaded into the MG by management
action and referenced by name in an EventsDescriptor, may be defined
dynamically and subsequently referenced by name, or the actual
digitmap itself may be specified in the EventsDescriptor. It is
permissible for a digit map completion event within an Events
Descriptor to refer by name to a DigitMap which is defined by a
DigitMap Descriptor within the same command, regardless of the
transmitted order of the respective descriptors.
DigitMaps defined in a DigitMapDescriptor can occur in any of the
standard Termination manipulation Commands of the protocol. A
DigitMap, once defined, can be used on all Terminations specified by
the (possibly wildcarded) TerminationID in such a command. DigitMaps
defined on the root Termination are global and can be used on every
Termination in the MG, provided that a DigitMap with the same name
has not been defined on the given Termination. When a DigitMap is
defined dynamically in a DigitMap Descriptor:
. A new DigitMap is created by specifying a name that is not yet
defined. The value shall be present.
. A DigitMap value is updated by supplying a new value for a name
that is already defined. Terminations presently using the
digitmap shall continue to use the old definition; subsequent
EventsDescriptors specifying the name, including any
EventsDescriptor in the command containing the DigitMap
descriptor, shall use the new one.
. A DigitMap is deleted by supplying an empty value for a name that
is already defined. Terminations presently using the digitmap
shall continue to use the old definition.
The collection of digits according to a DigitMap may be protected by
three timers, viz. a start timer (T), short timer (S), and long timer
(L).
Cuervo, et al. Standards Track [Page 34]
RFC 2885 Megaco Protocol August 2000
1. The start timer (T) is used prior to any digits having been
dialed.
2. If the Media Gateway can determine that at least one more digit is
needed for a digit string to match any of the allowed patterns in
the digit map, then the interdigit timer value should be set to a
long (L) duration (e.g. 16 seconds).
3. If the digit string has matched one of the patterns in a digit
map, but it is possible that more digits could be received which
would cause a match with a different pattern, then instead of
reporting the match immediately, the MG must apply the short timer
(S) and wait for more digits.
The timers are configurable parameters to a DigitMap. The Start
timer is started at the beginning of every digit map use, but can be
overridden.
The formal syntax of the digit map is described by the DigitMap rule
in the formal syntax description of the protocol (see Annex A and
Annex B). A DigitMap, according to this syntax, is defined either by
a string or by a list of strings. Each string in the list is an
alternative event sequence, specified either as a sequence of digit
map symbols or as a regular expression of digit map symbols. These
digit map symbols, the digits "0" through "9" and letters "A" through
a maximum value depending on the signalling system concerned, but
never exceeding "K", correspond to specified events within a package
which has been designated in the Events Descriptor on the termination
to which the digit map is being applied. (The mapping between events
and digit map symbols is defined in the documentation for packages
associated with channel-associated signalling systems such as DTMF,
MF, or R2. Digits "0" through "9" MUST be mapped to the
corresponding digit events within the signalling system concerned.
Letters should be allocated in logical fashion, facilitating the use
of range notation for alternative events.)
The letter "x" is used as a wildcard, designating any event
corresponding to symbols in the range "0"-"9". The string may also
contain explicit ranges and, more generally, explicit sets of
symbols, designating alternative events any one of which satisfies
that position of the digit map. Finally, the dot symbol "." stands
for zero or more repetitions of the event selector (event, range of
events, set of alternative events, or wildcard) that precedes it. As
a consequence of the third timing rule above, inter-event timing
while matching the dot symbol uses the short timer by default.
In addition to these event symbols, the string may contain "S" and
"L" inter-event timing specifiers and the "Z" duration modifier. "S"
Cuervo, et al. Standards Track [Page 35]
RFC 2885 Megaco Protocol August 2000
and "L" respectively indicate that the MG should use the short (S)
timer or the long (L) timer for subsequent events, over-riding the
timing rules described above. A timer specifier following a dot
specifies inter-event timing for all events matching the dot as well
as for subsequent events. If an explicit timing specifier is in
effect in one alternative event sequence, but none is given in any
other candidate alternative, the timer value set by the explicit
timing specifier must be used. If all sequences with explicit timing
controls are dropped from the candidate set, timing reverts to the
default rules given above. Finally, if conflicting timing specifiers
are in effect in different alternative sequences, the results are
undefined.
A "Z" designates a long duration event: placed in front of the
symbol(s) designating the event(s) which satisfy a given digit
position, it indicates that that position is satisfied only if the
duration of the event exceeds the long-duration threshold. The value
of this threshold is assumed to be provisioned in the MG.
A digit map is active while the events descriptor which invoked it is
active and it has not completed. A digit map completes when:
. a timer has expired, or
. an alternative event sequence has been matched and no other
alternative event sequence in the digit map could be matched
through detection of an additional event (unambiguous match), or
. an event has been detected such that a match to a complete
alternative event sequence of the digit map will be impossible no
matter what additional events are received.
Upon completion, a digit map completion event as defined in the
package providing the events being mapped into the digit map shall be
generated. At that point the digit map is deactivated. Subsequent
events in the package are processed as per the currently active event
processing mechanisms.
Pending completion, successive events shall be processed according to
the following rules:
1. The "current dial string", an internal variable, is initially
empty. The set of candidate alternative event sequences includes
all of the alternatives specified in the digit map.
2. At each step, a timer is set to wait for the next event, based
either on the default timing rules given above or on explicit
timing specified in one or more alternative event sequences. If
Cuervo, et al. Standards Track [Page 36]
RFC 2885 Megaco Protocol August 2000
the timer expires and a member of the candidate set of
alternatives is fully satisfied, a timeout completion with full
match is reported. If the timer expires and part or none of any
candidate alternative is satisfied, a timeout completion with
partial match is reported.
3. If an event is detected before the timer expires, it is mapped to
a digit string symbol and provisionally added to the end of the
current dial string. The duration of the event (long or not long)
is noted if and only if this is relevant in the current symbol
position (because at least one of the candidate alternative event
sequences includes the "Z" modifier at this position in the
sequence).
4. The current dial string is compared to the candidate alternative
event sequences. If and only if a sequence expecting a long-
duration event at this position is matched (i.e. the event had
long duration and met the specification for this position), then
any alternative event sequences not specifying a long duration
event at this position are discarded, and the current dial string
is modified by inserting a "Z" in front of the symbol representing
the latest event. Any sequence expecting a long-duration event at
this position but not matching the observed event is discarded
from the candidate set. If alternative event sequences not
specifying a long duration event in the given position remain in
the candidate set after application of the above rules, the
observed event duration is treated as irrelevant in assessing
matches to them.
5. If exactly one candidate remains, a completion event is generated
indicating an unambiguous match. If no candidates remain, the
latest event is removed from the current dial string and a
completion event is generated indicating full match if one of the
candidates from the previous step was fully satisfied before the
latest event was detected, or partial match otherwise. The event
removed from the current dial string will then be reported as per
the currently active event processing mechanisms.
6. If no completion event is reported out of step 5 (because the
candidate set still contains more than one alternative event
sequence), processing returns to step 2.
A digit map is activated whenever a new event descriptor is applied
to the termination or embedded event descriptor is activated, and
that event descriptor contains a digit map completion event which
itself contains a digit map parameter. Each new activation of a
digit map begins at step 1 of the above procedure, with a clear
current dial string. Any previous contents of the current dial
Cuervo, et al. Standards Track [Page 37]
RFC 2885 Megaco Protocol August 2000
string from an earlier activation are lost. While the digit map is
activated, detection is enabled for all events defined in the package
containing the specified digit map completion event. Normal event
behaviour (e.g. stopping of signals unless the digit completion event
has the KeepActive flag enabled) continues to apply for each such
event detected, except that the events in the package containing the
specified digit map completion event other than the completion event
itself are not individually notified.
Note that if a package contains a digit map completion event, then an
event specification consisting of the package name with a wildcarded
ItemID (Property Name) will activate a digit map if the event
includes a digit map parameter. Regardless of whether a digit map is
activated, this form of event specification will cause the individual
events to be reported to the MGC as they are detected.
As an example, consider the following dial plan:
0 Local operator
00 Long distance operator
xxxx Local extension number
(starts with 1-7)
8xxxxxxx Local number
#xxxxxxx Off-site extension
*xx Star services
91xxxxxxxxxx Long distance number
9011 + up to 15 digits International number
If the DTMF detection package described in Annex E (section E.6) is
used to collect the dialled digits, then the dialling plan shown
above results in the following digit map:
(0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)
The Statistics parameter provides information describing the status
and usage of a Termination during its existence within a specific
Context. There is a set of standard statistics kept for each
termination where appropriate (number of octets sent and received for
example). The particular statistical properties that are reported
for a given Termination are determined by the Packages realized by
the Termination. By default, statistics are reported when the
Termination is Subtracted from the Context. This behavior can be
overridden by including an empty AuditDescriptor in the Subtract
command. Statistics may also be returned from the AuditValue
command, or any Add/Move/Modify command using the Audit descriptor.
Cuervo, et al. Standards Track [Page 38]
RFC 2885 Megaco Protocol August 2000
Statistics are cumulative; reporting Statistics does not reset them.
Statistics are reset when a Termination is Subtracted from a Context.
ObservedEvents is supplied with the Notify command to inform the MGC
of which event(s) were detected. Used with the AuditValue command,
the ObservedEventsDescriptor returns events in the event buffer which
have not been Notified. ObservedEvents contains the RequestIdentifier
of the EventsDescriptor that triggered the notification, the event(s)
detected and the detection time(s). Detection times are reported
with a precision of hundredths of a second. Time is expressed in
UTC.
A topology descriptor is used to specify flow directions between
terminations in a Context. Contrary to the descriptors in previous
sections, the topology descriptor applies to a Context instead of a
Termination. The default topology of a Context is that each
termination's transmission is received by all other terminations.
The Topology Descriptor is optional to implement.
The Topology Descriptor occurs before the commands in an action. It
is possible to have an action containing only a Topology Descriptor,
provided that the context to which the action applies already exists.
A topology descriptor consists of a sequence of triples of the form
(T1, T2, association). T1 and T2 specify Terminations within the
Context, possibly using the ALL or CHOOSE wildcard. The association
specifies how media flows between these two Terminations as follows.
. (T1, T2, isolate) means that the Terminations matching T2 do not
receive media from the Terminations matching T1, nor vice versa.
. (T1, T2, oneway) means that the Terminations that match T2
receive media from the Terminations matching T1, but not vice
versa. In this case use of the ALL wildcard such that there are
Terminations that match both T1 and T2 is not allowed.
. (T1, T2, bothway) means that the Terminations matching T2 receive
media from the Terminations matching T1, and vice versa. In this
case it is allowed to use wildcards such that there are
Cuervo, et al. Standards Track [Page 39]
RFC 2885 Megaco Protocol August 2000
Terminations that match both T1 and T2. However, if there is a
Termination that matches both, no loopback is introduced;
loopbacks are created by setting the TerminationMode. CHOOSE
wildcards may be used in T1 and T2 as well, under the following
restrictions:
. the action (see section 8) of which the topology descriptor is
part contains an Add command in which a CHOOSE wildcard is used;
. if a CHOOSE wildcard occurs in T1 or T2, then a partial name
SHALL NOT be specified.
The CHOOSE wildcard in a topology descriptor matches the
TerminationID that the MG assigns in the first Add command that uses
a CHOOSE wildcard in the same action. An existing Termination that
matches T1 or T2 in the Context to which a Termination is added, is
connected to the newly added Termination as specified by the topology
descriptor. The default association when a termination is not
mentioned in the Topology descriptor is bothway (if T3 is added to a
context with T1 and T2 with topology (T3,T1,oneway) it will be
connected bothway to T2).
Cuervo, et al. Standards Track [Page 40]
RFC 2885 Megaco Protocol August 2000
The figure below and the table following it show some examples of the
effect of including topology descriptors in actions. In these
examples it is assumed that the topology descriptors are applied in
sequence.
Context 1 Context 2 Context 3
+------------------+ +------------------+ +------------------+
| +----+ | | +----+ | | +----+ |
| | T2 | | | | T2 | | | | T2 | |
| +----+ | | +----+ | | +----+ |
| ^ ^ | | ^ | | ^ |
| | | | | | | | | |
| +--+ +--+ | | +---+ | | +--+ |
| | | | | | | | | |
| v v | | v | | | |
| +----+ +----+ | | +----+ +----+ | | +----+ +----+ |
| | T1 |<-->| T3 | | | | T1 |<-->| T3 | | | | T1 |<-->| T3 | |
| +----+ +----+ | | +----+ +----+ | | +----+ +----+ |
+------------------+ +------------------+ +------------------+
1. No Topology Desc. 2. T1, T2 Isolate 3. T3, T2 oneway
Context 1 Context 2 Context 3
+------------------+ +------------------+ +------------------+
| +----+ | | +----+ | | +----+ |
| | T2 | | | | T2 | | | | T2 | |
| +----+ | | +----+ | | +----+ |
| | | | ^ | | ^ ^ |
| | | | | | | | | |
| +--+ | | +---+ | | +--+ +--+ |
| | | | | | | | | |
| v | | v | | v v |
| +----+ +----+ | | +----+ +----+ | | +----+ +----+ |
| | T1 |<-->| T3 | | | | T1 |<-->| T3 | | | | T1 |<-->| T3 | |
| +----+ +----+ | | +----+ +----+ | | +----+ +----+ |
+------------------+ +------------------+ +------------------+
4. T2, T3 oneway 5. T2, T3 bothway 6. T1, T2 bothway
Figure 4: A Sequence Of Example Topologies
Cuervo, et al. Standards Track [Page 41]
RFC 2885 Megaco Protocol August 2000
Topology Description
1 No topology descriptors
When no topology descriptors are included, all
terminations have a both way connection to all
other terminations.
2 T1, T2, Isolate
Removes the connection between T1 and T2.
T3 has a both way connection with both T1 and
T2. T1 and T2 have bothway connection to T3.
3 T3, T2, oneway
A oneway connection from T3 to T2 (i.e. T2
receives media flow from T3). A bothway
connection between T1 and T3.
4 T2, T3, oneway
A oneway connection between T2 to T3.
T1 and T3 remain bothway connected
5 T2, T3 bothway
T2 is bothway connected to T3. This results in
the same as 2.
6 T1, T2 bothway (T2, T3 bothway
and T1,T3 bothway may be implied
or explicit).
All terminations have a bothway connection to
all other terminations.
A oneway connection must implemented in such a way that the other
Terminations in the Context are not aware of the change in topology.
Following is an Application Programming Interface (API) describing
the Commands of the protocol. This API is shown to illustrate the
Commands and their parameters and is not intended to specify
implementation (e.g. via use of blocking function calls). It
describes the input parameters in parentheses after the command name
and the return values in front of the Command. This is only for
descriptive purposes; the actual Command syntax and encoding are
specified in later subsections. All parameters enclosed by square
brackets ([. . . ]) are considered optional.
Cuervo, et al. Standards Track [Page 42]
RFC 2885 Megaco Protocol August 2000
The Add Command adds a Termination to a Context.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Add( TerminationID
[, MediaDescriptor]
[, ModemDescriptor]
[, MuxDescriptor]
[, EventsDescriptor]
[, SignalsDescriptor]
[, DigitMapDescriptor]
[, AuditDescriptor]
)
The TerminationID specifies the termination to be added to the
Context. The Termination is either created, or taken from the null
Context. For an existing Termination, the TerminationID would be
specific. For a Termination that does not yet exist, the
TerminationID is specified as CHOOSE in the command. The new
TerminationID will be returned. Wildcards may be used in an Add, but
such usage would be unusual. If the wildcard matches more than one
TerminationID, all possible matches are attempted, with results
reported for each one. The order of attempts when multiple
TerminationIDs match is not specified.
The optional MediaDescriptor describes all media streams.
The optional ModemDescriptor and MuxDescriptor specify a modem and
multiplexer if applicable. For convenience, if a Multiplex Descriptor
is present in an Add command and lists any Terminations that are not
currently in the Context, such Terminations are added to the context
as if individual Add commands listing the Terminations were invoked.
If an error occurs on such an implied Add, error 471 - Implied Add
for Multiplex failure shall be returned and further processing of the
command shall cease.
Cuervo, et al. Standards Track [Page 43]
RFC 2885 Megaco Protocol August 2000
The EventsDescriptor parameter is optional. If present, it provides
the list of events that should be detected on the Termination.
The SignalsDescriptor parameter is optional. If present, it provides
the list of signals that should be applied to the Termination.
The DigitMapDescriptor parameter is optional. If present, defines a
DigitMap definition that may be used in an EventsDescriptor.
The AuditDescriptor is optional. If present, the command will return
descriptors as specified in the AuditDescriptor.
All descriptors that can be modified could be returned by MG if a
parameter was underspecified or overspecified. ObservedEvents,
Statistics, and Packages, and the EventBuffer Descriptors are
returned only if requested in the AuditDescriptor. Add SHALL NOT be
used on a Termination with a serviceState of "OutofService".
The Modify Command modifies the properties of a Termination.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Modify( TerminationID
[, MediaDescriptor]
[, ModemDescriptor]
[, MuxDescriptor]
[, EventsDescriptor]
[, SignalsDescriptor]
[, DigitMapDescriptor]
[, AuditDescriptor]
)
The TerminationID may be specific if a single Termination in the
Context is to be modified. Use of wildcards in the TerminationID may
be appropriate for some operations. If the wildcard matches more than
one TerminationID, all possible matches are attempted, with results
reported for each one. The order of attempts when multiple
Cuervo, et al. Standards Track [Page 44]
RFC 2885 Megaco Protocol August 2000
TerminationIDs match is not specified. The CHOOSE option is an error,
as the Modify command may only be used on existing Terminations.
The remaining parameters to Modify are the same as those to Add.
Possible return values are the same as those to Add.
The Subtract Command disconnects a Termination from its Context and
returns statistics on the Termination's participation in the Context.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Subtract(TerminationID
[, AuditDescriptor]
)
TerminationID in the input parameters represents the Termination that
is being subtracted. The TerminationID may be specific or may be a
wildcard value indicating that all (or a set of related) Terminations
in the Context of the Subtract Command are to be subtracted. If the
wildcard matches more than one TerminationID, all possible matches
are attempted, with results reported for each one. The order of
attempts when multiple TerminationIDs match is not specified. The
CHOOSE option is an error, as the Subtract command may only be used
on existing Terminations. ALL may be used as the ContextID as well
as the TerminationId in a Subtract, which would have the effect of
deleting all contexts, deleting all ephemeral terminations, and
returning all physical terminations to Null context.
By default, the Statistics parameter is returned to report
information collected on the Termination or Terminations specified in
the Command. The information reported applies to the Termination's
or Terminations' existence in the Context from which it or they are
being subtracted.
The AuditDescriptor is optional. If present, the command will return
descriptors as specified in the AuditDescriptor. Possible return
values are the same as those to Add.
Cuervo, et al. Standards Track [Page 45]
RFC 2885 Megaco Protocol August 2000
When a provisioned Termination is Subtracted from a context, its
property values shall revert to:
. the default value, if specified for the property and not
overridden by provisioning,
. otherwise, the provisioned value.
The Move Command moves a Termination to another Context from its
current Context in one atomic operation. The Move command is the
only command that refers to a Termination in a Context different from
that to which the command is applied. The Move command shall not be
used to move Terminations to or from the null Context.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
Move( TerminationID
[, MediaDescriptor]
[, ModemDescriptor]
[, MuxDescriptor]
[, EventsDescriptor]
[, SignalsDescriptor]
[, DigitMapDescriptor]
[, AuditDescriptor]
)
The TerminationID specifies the Termination to be moved. It may be
wildcarded. If the wildcard matches more than one TerminationID, all
possible matches are attempted, with results reported for each one.
The order of attempts when multiple TerminationIDs match is not
specified. By convention, the Termination is subtracted from its
previous Context. The Context to which the Termination is moved is
indicated by the target ContextId in the Action. If the last
remaining Termination is moved out of a Context, the Context is
deleted.
Cuervo, et al. Standards Track [Page 46]
RFC 2885 Megaco Protocol August 2000
The remaining descriptors are processed as in the Modify Command.
The AuditDescriptor with the Statistics option, for example, would
return statistics on the Termination just prior to the Move.
Possible descriptors returned from Move are the same as for Add.
Move SHALL NOT be used on a Termination with a serviceState of
"OutofService".
The AuditValue Command returns the current values of properties,
events, signals and statistics associated with Terminations.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,DigitMapDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
[,StatisticsDescriptor]
[,PackagesDescriptor]
AuditValue(TerminationID,
AuditDescriptor
)
TerminationID may be specific or wildcarded. If the wildcard matches
more than one TerminationID, all possible matches are attempted, with
results reported for each one. The order of attempts when multiple
TerminationIDs match is not specified. If a wildcarded response is
requested, only one command return is generated, with the contents
containing the union of the values of all Terminations matching the
wildcard. This convention may reduce the volume of data required to
audit a group of Terminations. Use of CHOOSE is an error.
The appropriate descriptors, with the current values for the
Termination, are returned from AuditValue. Values appearing in
multiple instances of a descriptor are defined to be alternate values
supported, with each parameter in a descriptor considered
independent.
ObservedEvents returns a list of events in the EventBuffer,
PackagesDescriptor returns a list of packages realized by the
Termination. DigitMapDescriptor returns the name or value of the
current DigitMap for the Termination. DigitMap requested in an
AuditValue command with TerminationID ALL returns all DigitMaps in
the gateway. Statistics returns the current values of all statistics
Cuervo, et al. Standards Track [Page 47]
RFC 2885 Megaco Protocol August 2000
being kept on the Termination. Specifying an empty Audit Descriptor
results in only the TerminationID being returned. This may be useful
to get a list of TerminationIDs when used with wildcard.
AuditValue results depend on the Context, viz. specific, null, or
wildcarded. The TerminationID may be specific, or wildcarded. The
following illustrates other information that can be obtained with the
Audit Command:
ContextID TerminationID Information Obtained
Specific wildcard Audit of matching
Terminations in a Context
Specific specific Audit of a single
Termination in a Context
Null Root Audit of Media Gateway state
and events
Null wildcard Audit of all matching
Terminations in the Null
Context
Null specific Audit of a single
Termination outside of any
Context
All wildcard Audit of all matching
Terminations and the Context
to which they are associated
All Root List of all ContextIds
The AuditCapabilities Command returns the possible values of
properties, events, signals and statistics associated with
Terminations.
TerminationID
[,MediaDescriptor]
[,ModemDescriptor]
[,MuxDescriptor]
[,EventsDescriptor]
[,SignalsDescriptor]
[,ObservedEventsDescriptor]
[,EventBufferDescriptor]
Cuervo, et al. Standards Track [Page 48]
RFC 2885 Megaco Protocol August 2000
[,StatisticsDescriptor]
AuditCapabilities(TerminationID,
AuditDescriptor
)
The appropriate descriptors, with the possible values for the
Termination are returned from AuditCapabilities. Descriptors may be
repeated where there are multiple possible values. If a wildcarded
response is requested, only one command return is generated, with the
contents containing the union of the values of all Terminations
matching the wildcard. This convention may reduce the volume of data
required to audit a group of Terminations.
Interpretation of what capabilities are requested for various values
of ContextID and TerminationID is the same as in AuditValue.
The EventsDescriptor returns the list of possible events on the
Termination together with the list of all possible values for the
EventsDescriptor Parameters. The SignalsDescriptor returns the list
of possible signals that could be applied to the Termination together
with the list of all possible values for the Signals Parameters.
StatisticsDescriptor returns the names of the statistics being kept
on the termination. ObservedEventsDescriptor returns the names of
active events on the termination. DigitMap and Packages are not
legal in AuditCapability.
The Notify Command allows the Media Gateway to notify the Media
Gateway Controller of events occurring within the Media Gateway.
Notify(TerminationID,
ObservedEventsDescriptor,
[ErrorDescriptor]
)
The TerminationID parameter specifies the Termination issuing the
Notify Command. The TerminationID shall be a fully qualified name.
The ObservedEventsDescriptor contains the RequestID and a list of
events that the Media Gateway detected in the order that they were
detected. Each event in the list is accompanied by parameters
associated with the event and an indication of the time that the
event was detected. Procedures for sending Notify commands with
RequestID equal to 0 are for further study.
Cuervo, et al. Standards Track [Page 49]
RFC 2885 Megaco Protocol August 2000
Notify Commands with RequestID not equal to 0 shall occur only as the
result of detection of an event specified by an Events Descriptor
which is active on the termination concerned.
The RequestID returns the RequestID parameter of the EventsDescriptor
that triggered the Notify Command. It is used to correlate the
notification with the request that triggered it. The events in the
list must have been requested via the triggering EventsDescriptor or
embedded events descriptor unless the RequestID is 0 (which is for
further study).
The ServiceChange Command allows the Media Gateway to notify the
Media Gateway Controller that a Termination or group of Terminations
is about to be taken out of service or has just been returned to
service. The Media Gateway Controller may indicate that
Termination(s) shall be taken out of or returned to service. The
Media Gateway may notify the MGC that the capability of a Termination
has changed. It also allows a MGC to hand over control of a MG to
another MGC.
TerminationID,
[ServiceChangeDescriptor]
ServiceChange(TerminationID,
ServiceChangeDescriptor
)
The TerminationID parameter specifies the Termination(s) that are
taken out of or returned to service. Wildcarding of Termination
names is permitted, with the exception that the CHOOSE mechanism
shall not be used. Use of the "Root" TerminationID indicates a
ServiceChange affecting the entire Media Gateway.
The ServiceChangeDescriptor contains the following parameters as
required:
. ServiceChangeMethod
. ServiceChangeReason
. ServiceChangeDelay
. ServiceChangeAddress
. ServiceChangeProfile
. ServiceChangeVersion
. ServiceChangeMgcId
. TimeStamp
The ServiceChangeMethod parameter specifies the type of ServiceChange
that will or has occurred:
Cuervo, et al. Standards Track [Page 50]
RFC 2885 Megaco Protocol August 2000
1) Graceful - indicates that the specified Terminations will be taken
out of service after the specified ServiceChangeDelay; established
connections are not yet affected, but the Media Gateway Controller
should refrain from establishing new connections and should
attempt to gracefully tear down existing connections. The MG
should set termination serviceState at the expiry of
ServiceChangeDelay or the removal of the termination from an
active context (whichever is first), to "out of service".
2) Forced - indicates that the specified Terminations were taken
abruptly out of service and any established connections associated
with them were lost. The MGC is responsible for cleaning up the
context (if any) with which the failed termination is associated.
At a minimum the termination shall be subtracted from the context.
The termination serviceState should be "out of service".
3) Restart - indicates that service will be restored on the specified
Terminations after expiration of the ServiceChangeDelay. The
serviceState should be set to "inService" upon expiry of
ServiceChangeDelay.
4) Disconnected - always applied with the Root TerminationID,
indicates that the MG lost communication with the MGC, but it was
subsequently restored. Since MG state may have changed, the MGC
may wish to use the Audit command to resynchronize its state with
the MG's.
5) Handoff - sent from the MGC to the MG, this reason indicates that
the MGC is going out of service and a new MGC association must be
established. Sent from the MG to the MGC, this indicates that the
MG is attempting to establish a new association in accordance with
a Handoff received from the MGC with which it was previously
associated.
6) Failover - sent from MG to MGC to indicate the primary MG is out
of service and a secondary MG is taking over.
7) Another value whose meaning is mutually understood between the MG
and the MGC.
The ServiceChangeReason parameter specifies the reason why the
ServiceChange has or will occur. It consists of an alphanumeric
token (IANA registered) and an explanatory string.
The optional ServiceChangeAddress parameter specifies the address
(e.g., IP port number for IP networks) to be used for subsequent
communications. It can be specified in the input parameter
descriptor or the returned result descriptor. ServiceChangeAddress
Cuervo, et al. Standards Track [Page 51]
RFC 2885 Megaco Protocol August 2000
and ServiceChangeMgcId parameters must not both be present in the
ServiceChangeDescriptor or the ServiceChangeResultDescriptor. The
serviceChangeAddress provides an address to be used within the
context of the association currently being negotiated, while the
ServiceChangeMgcId provides an alternate address where the MG should
seek to establish another association.
The optional ServiceChangeDelay parameter is expressed in seconds.
If the delay is absent or set to zero, the delay value should be
considered to be null. In the case of a "graceful"
ServiceChangeMethod, a null delay indicates that the Media Gateway
Controller should wait for the natural removal of existing
connections and should not establish new connections. . For
"graceful" only, a null delay means the MG must not set serviceState
"out of service" until the termination is in the null context.
The optional ServiceChangeProfile parameter specifies the Profile (if
any) of the protocol supported. The ServiceChangeProfile includes
the version of the profile supported.
The optional ServiceChangeVersion parameter contains the protocol
version and is used if protocol version negotiation occurs (see
section 11.3).
The optional TimeStamp parameter specifies the actual time as kept by
the sender. It can be used by the responder to determine how its
notion of time differs from that of its correspondent. TimeStamp is
sent with a precision of hundredths of a second, and is expressed in
UTC.
The optional Extension parameter may contain any value whose meaning
is mutually understood by the MG and MGC.
A ServiceChange Command specifying the "Root" for the TerminationID
and ServiceChangeMethod equal to Restart is a registration command by
which a Media Gateway announces its existence to the Media Gateway
Controller. The Media Gateway is expected to be provisioned with the
name of one primary and optionally some number of alternate Media
Gateway Controllers. Acknowledgement of the ServiceChange Command
completes the registration process. The MG may specify the transport
ServiceChangeAddress to be used by the MGC for sending messages in
the ServiceChangeAddress parameter in the input
ServiceChangeDescriptor. The MG may specify an address in the
ServiceChangeAddress parameter of the ServiceChange request, and the
MGC may also do so in the ServiceChange reply. In either case, the
recipient must use the supplied address as the destination for all
subsequent transaction requests within the association. At the same
time, as indicated in section 9, transaction replies and pending
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indications must be sent to the address from which the corresponding
requests originated. This must be done even if it implies extra
messaging because commands and responses cannot be packed together.
The TimeStamp parameter shall be sent with a registration command and
its response.
The Media Gateway Controller may return an ServiceChangeMgcId
parameter that describes the Media Gateway Controller that should
preferably be contacted for further service by the Media Gateway. In
this case the Media Gateway shall reissue the ServiceChange command
to the new Media Gateway Controller. The Gateway specified in an
ServiceChangeMgcId, if provided, shall be contacted before any
further alternate MGCs. On a HandOff message from MGC to MG, the
ServiceChangeMgcId is the new MGC that will take over from the
current MGC.
The return from ServiceChange is empty except when the Root
terminationID is used. In that case it includes the following
parameters as required:
. ServiceChangeAddress, if the responding MGC wishes to specify an
new destination for messages from the MG for the remainder of the
association;
. ServiceChangeMgcId, if the responding MGC does not wish to
sustain an association with the MG;
. ServiceChangeProfile, if the responder wishes to negotiate the
profile to be used for the association;
. ServiceChangeVersion, if the responder wishes to negotiate the
version of the protocol to be used for the association.
The following ServiceChangeReasons are defined. This list may be
extended by an IANA registration as outlined in section 13.3
900 Service Restored
901 Cold Boot
902 Warm Boot
903 MGC Directed Change
904 Termination malfunctioning
905 Termination taken out of service
906 Loss of lower layer connectivity (e.g. downstream sync)
907 Transmission Failure
908 MG Impending Failure
909 MGC Impending Failure
910 Media Capability Failure
911 Modem Capability Failure
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912 Mux Capability Failure
913 Signal Capability Failure
914 Event Capability Failure
915 State Loss
The commands of the protocol as discussed in the preceding sections
apply to terminations. This section specifies how contexts are
manipulated and audited.
Commands are grouped into actions (see section 8). An action applies
to one context. In addition to commands, an action may contain
context manipulation and auditing instructions.
An action request sent to a MG may include a request to audit
attributes of a context. An action may also include a request to
change the attributes of a context.
The context properties that may be included in an action reply are
used to return information to a MGC. This can be information
requested by an audit of context attributes or details of the effect
of manipulation of a context.
If a MG receives an action which contains both a request to audit
context attributes and a request to manipulate those attributes, the
response SHALL include the values of the attributes after processing
the manipulation request.
The protocol can be encoded in a binary format or in a text format.
MGCs should support both encoding formats. MGs may support both
formats.
The protocol syntax for the binary format of the protocol is defined
in Annex A. Annex C specifies the encoding of the Local and Remote
descriptors for use with the binary format.
A complete ABNF of the text encoding of the protocol per RFC2234 is
given in Annex B. SDP is used as the encoding of the Local and
Remote Descriptors for use with the text encoding as modified in
section 7.1.8.
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Errors consist of an IANA registered error code and an explanatory
string. Sending the explanatory string is optional. Implementations
are encouraged to append diagnostic information to the end of the
string.
When a MG reports an error to a MGC, it does so in an error
descriptor. An error descriptor consists of an error code and
optionally the associated explanatory string.
The identified error codes are:
400 - Bad Request
401 - Protocol Error
402 - Unauthorized
403 - Syntax Error in Transaction
404 - Syntax Error in TransactionReply
405 - Syntax Error in TransactionPending
406 - Version Not Supported
410 - Incorrect identifier
411 - The transaction refers to an unknown ContextId
412 - No ContextIDs available
421 - Unknown action or illegal combination of actions
422 - Syntax Error in Action
430 - Unknown TerminationID
431 - No TerminationID matched a wildcard
432 - Out of TerminationIDs or No TerminationID available
433 - TerminationID is already in a Context
440 - Unsupported or unknown Package
441 - Missing RemoteDescriptor
442 - Syntax Error in Command
443 - Unsupported or Unknown Command
444 - Unsupported or Unknown Descriptor
445 - Unsupported or Unknown Property
446 - Unsupported or Unknown Parameter
447 - Descriptor not legal in this command
448 - Descriptor appears twice in a command
450 - No such property in this package
451 - No such event in this package
452 - No such signal in this package
453 - No such statistic in this package
454 - No such parameter value in this package
455 - Parameter illegal in this Descriptor
456 - Parameter or Property appears twice in this Descriptor
461 - TransactionIDs in Reply do not match Request
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462 - Commands in Transaction Reply do not match commands in
request
463 - TerminationID of Transaction Reply does not match
request
464 - Missing reply in Transaction Reply
465 - TransactionID in Transaction Pending does not match any
open request
466 - Illegal Duplicate Transaction Request
467 - Illegal Duplicate Transaction Reply
471 - Implied Add for Multiplex failure
500 - Internal Gateway Error
501 - Not Implemented
502 - Not ready.
503 - Service Unavailable
504 - Command Received from unauthorized entity
505 - Command Received before Restart Response
510 - Insufficient resources
512 - Media Gateway unequipped to detect requested Event
513 - Media Gateway unequipped to generate requested Signals
514 - Media Gateway cannot send the specified announcement
515 - Unsupported Media Type
517 - Unsupported or invalid mode
518 - Event buffer full
519 - Out of space to store digit map
520 - Media Gateway does not have a digit map
521 - Termination is "ServiceChangeing"
526 - Insufficient bandwidth
529 - Internal hardware failure
530 - Temporary Network failure
531 - Permanent Network failure
581 - Does Not Exist
Commands between the Media Gateway Controller and the Media Gateway
are grouped into Transactions, each of which is identified by a
TransactionID. Transactions consist of one or more Actions. An
Action consists of a series of Commands that are limited to operating
within a single Context. Consequently each Action typically
specifies a ContextID. However, there are two circumstances where a
specific ContextID is not provided with an Action. One is the case
of modification of a Termination outside of a Context. The other is
where the controller requests the gateway to create a new Context.
Following is a graphic representation of the Transaction, Action and
Command relationships.
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+----------------------------------------------------------+
| Transaction x |
| +----------------------------------------------------+ |
| | Action 1 | |
| | +---------+ +---------+ +---------+ +---------+ | |
| | | Command | | Command | | Command | | Command | | |
| | | 1 | | 2 | | 3 | | 4 | | |
| | +---------+ +---------+ +---------+ +---------+ | |
| +----------------------------------------------------+ |
| |
| +----------------------------------------------------+ |
| | Action 2 | |
| | +---------+ | |
| | | Command | | |
| | | 1 | | |
| | +---------+ | |
| +----------------------------------------------------+ |
| |
| +----------------------------------------------------+ |
| | Action 3 | |
| | +---------+ +---------+ +---------+ | |
| | | Command | | Command | | Command | | |
| | | 1 | | 2 | | 3 | | |
| | +---------+ +---------+ +---------+ | |
| +----------------------------------------------------+ |
+----------------------------------------------------------+
Figure 5 Transactions, Actions and Commands
Transactions are presented as TransactionRequests. Corresponding
responses to a TransactionRequest are received in a single reply,
possibly preceded by a number of TransactionPending messages (see
section 8.2.3).
Transactions guarantee ordered Command processing. That is, Commands
within a Transaction are executed sequentially. Ordering of
Transactions is NOT guaranteed - transactions may be executed in any
order, or simultaneously.
At the first failing Command in a Transaction, processing of the
remaining Commands in that Transaction stops. If a command contains
a wildcarded TerminationID, the command is attempted with each of the
actual TerminationIDs matching the wildcard. A response within the
TransactionReply is included for each matching TerminationID, even if
one or more instances generated an error. If any TerminationID
matching a wildcard results in an error when executed, any commands
following the wildcarded command are not attempted. Commands may be
marked as "Optional" which can override this behaviour - if a
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command marked as Optional results in an error, subsequent commands
in the Transaction will be executed. A TransactionReply includes the
results for all of the Commands in the corresponding
TransactionRequest. The TransactionReply includes the return values
for the Commands that were executed successfully, and the Command and
error descriptor for any Command that failed. TransactionPending is
used to periodically notify the receiver that a Transaction has not
completed yet, but is actively being processed.
Applications SHOULD implement an application level timer per
transaction. Expiration of the timer should cause a retransmission
of the request. Receipt of a Reply should cancel the timer. Receipt
of Pending should restart the timer.
Contexts are identified by a ContextID, which is assigned by the
Media Gateway and is unique within the scope of the Media Gateway.
The Media Gateway Controller shall use the ContextID supplied by the
Media Gateway in all subsequent Transactions relating to that
Context. The protocol makes reference to a distinguished value that
may be used by the Media Gateway Controller when referring to a
Termination that is currently not associated with a Context, namely
the null ContextID.
The CHOOSE wildcard is used to request that the Media Gateway create
a new Context. The MGC shall not use partially specified ContextIDs
containing the CHOOSE wildcard.
The MGC may use the ALL wildcard to address all Contexts on the MG.
Following is an Application Programming Interface (API) describing
the Transactions of the protocol. This API is shown to illustrate
the Transactions and their parameters and is not intended to specify
implementation (e.g. via use of blocking function calls). It will
describe the input parameters and return values expected to be used
by the various Transactions of the protocol from a very high level.
Transaction syntax and encodings are specified in later subsections.
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The TransactionRequest is invoked by the sender. There is one
Transaction per request invocation. A request contains one or more
Actions, each of which specifies its target Context and one or more
Commands per Context.
TransactionRequest(TransactionId {
ContextID {Command _ Command},
. . .
ContextID {Command _ Command } })
The TransactionID parameter must specify a value for later
correlation with the TransactionReply or TransactionPending response
from the receiver.
The ContextID parameter must specify a value to pertain to all
Commands that follow up to either the next specification of a
ContextID parameter or the end of the TransactionRequest, whichever
comes first.
The Command parameter represents one of the Commands mentioned in the
"Command Details" subsection titled "Application Programming
Interface".
The TransactionReply is invoked by the receiver. There is one reply
invocation per transaction. A reply contains one or more Actions,
each of which must specify its target Context and one or more
Responses per Context.
TransactionReply(TransactionID {
ContextID { Response _ Response },
. . .
ContextID { Response _ Response } })
The TransactionID parameter must be the same as that of the
corresponding TransactionRequest.
The ContextID parameter must specify a value to pertain to all
Responses for the action. The ContextID may be specific or null.
Each of the Response parameters represents a return value as
mentioned in section 7.2, or an error descriptor if the command
execution encountered an error. Commands after the point of failure
are not processed and, therefore, Responses are not issued for them.
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An exception to this occurs if a command has been marked as optional
in the Transaction request. If the optional command generates an
error, the transaction still continues to execute, so the Reply
would, in this case, have Responses after an Error.
If the receiver encounters an error in processing a ContextID, the
requested Action response will consist of the context ID and a single
error descriptor, 422 Syntax Error in Action.
If the receiver encounters an error such that it cannot determine a
legal Action, it will return a TransactionReply consisting of the
TransactionID and a single error descriptor, 422 Syntax Error in
Action. If the end of an action cannot be reliably determined but one
or more Actions can be parsed, it will process them and then send 422
Syntax Error in Action as the last action for the transaction. If
the receiver encounters an error such that is cannot determine a
legal Transaction, it will return a TransactionReply with a null
TransactionID and a single error descriptor (403 Syntax Error in
Transaction).
If the end of a transaction can not be reliably determined and one or
more Actions can be parsed, it will process them and then return 403
Syntax Error in Transaction as the last action reply for the
transaction. If no Actions can be parsed, it will return 403 Syntax
Error in Transaction as the only reply
If the terminationID cannot be reliably determined it will send 442
Syntax Error in Command as the action reply.
If the end of a command cannot be reliably determined it will return
442 Syntax Error in Transaction as the reply to the last action it
can parse.
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
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by the MGC to indicate the interval within which the MG should
expects a response to any transaction from the MGC. Senders may
receive more than one TransactionPending for a command. If a
duplicate request is received when pending, the responder may send a
duplicate pending immediately, or continue waiting for its timer to
trigger another Transaction Pending.
Multiple Transactions can be concatenated into a Message. Messages
have a header, which includes the identity of the sender. The Message
Identifier (MID) of a message is set to a provisioned name (e.g.
domain address/domain name/device name) of the entity transmitting
the message. Domain name is a suggested default.
Every Message contains a Version Number identifying the version of
the protocol the message conforms to. Versions consist of one or two
digits, beginning with version 1 for the present version of the
protocol.
The transactions in a message are treated independently. There is no
order implied, there is no application or protocol acknowledgement of
a message.
The transport mechanism for the protocol should allow the reliable
transport of transactions between an MGC and MG. The transport shall
remain independent of what particular commands are being sent and
shall be applicable to all application states. There are several
transports defined for the protocol, which are defined in normative
Annexes to this document. Additional Transports may be defined as
additional annexes in subsequent editions of this document, or in
separate documents. For transport of the protocol over IP, MGCs
shall implement both TCP and UDP/ALF, an MG shall implement TCP or
UDP/ALF or both.
The MG is provisioned with a name or address (such as DNS name or IP
address) of a primary and zero or more secondary MGCs (see section
7.2.8) that is the address the MG uses to send messages to the MGC.
If TCP or UDP is used as the protocol transport and the port to which
the initial ServiceChange request is to be sent is not otherwise
known, that request should be sent to the default port number for the
protocol. This port number is 2944 for text-encoded operation or
2945 for binary-encoded operation, for either UDP or TCP. The MGC
receives the message containing the ServiceChange request from the MG
and can determine the MG's address from it. As described in section
7.2.8, either the MG or the MGC may supply an address in the
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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.
This document does not mandate that the underlying transport protocol
guarantees the sequencing of transactions sent to an entity. This
property tends to maximize the timeliness of actions, but it has a
few drawbacks. For example:
. Notify commands may be delayed and arrive at the MGC after the
transmission of a new command changing the EventsDescriptor
. If a new command is transmitted before a previous one is
acknowledged, there is no guarantee that prior command will be
executed before the new one.
Media Gateway Controllers that want to guarantee consistent operation
of the Media Gateway may use the following rules. These rules are
with respect to commands that are in different transactions.
Commands that are in the same transaction are executed in order (see
section 8).
1. When a Media Gateway handles several Terminations, commands
pertaining to the different Terminations may be sent in parallel,
for example following a model where each Termination (or group of
Terminations) is controlled by its own process or its own thread.
2. On a Termination, there should normally be at most one outstanding
command (Add or Modify or Move), unless the outstanding commands
are in the same transaction. However, a Subtract command may be
issued at any time. In consequence, a Media Gateway may sometimes
receive a Modify command that applies to a previously subtracted
Termination. Such commands should be ignored, and an error code
should be returned.
3. On a given Termination, there should normally be at most one
outstanding Notify command at any time.
4. In some cases, an implicitly or explicitly wildcarded Subtract
command that applies to a group of Terminations may step in front
of a pending Add command. The Media Gateway Controller should
individually delete all Terminations for which an Add command was
pending at the time of the global Subtract command. Also, new Add
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commands for Terminations named by the wild-carding (or implied in
a Multiplex descriptor) should not be sent until the wild-carded
Subtract command is acknowledged.
5. AuditValue and AuditCapability are not subject to any sequencing.
6. ServiceChange shall always be the first command sent by a MG as
defined by the restart procedure. Any other command or response
must be delivered after this ServiceChange command.
These rules do not affect the command responder, which should always
respond to commands.
In the event that a large number of Media Gateways are powered on
simultaneously and they were to all initiate a ServiceChange
transaction, the Media Gateway Controller would very likely be
swamped, leading to message losses and network congestion during the
critical period of service restoration. In order to prevent such
avalanches, the following behavior is suggested:
1. When a Media Gateway is powered on, it should initiate a restart
timer to a random value, uniformly distributed between 0 and a
maximum waiting delay (MWD). Care should be taken to avoid
synchronicity of the random number generation between multiple
Media Gateways that would use the same algorithm.
2. The Media Gateway should then wait for either the end of this
timer or the detection of a local user activity, such as for
example an off-hook transition on a residential Media Gateway.
3. When the timer elapses, or when an activity is detected, the Media
Gateway should initiate the restart procedure.
The restart procedure simply requires the MG to guarantee that the
first message that the Media Gateway Controller sees from this MG is
a ServiceChange message informing the Media Gateway Controller about
the restart.
Note - The value of MWD is a configuration parameter that depends on
the type of the Media Gateway. The following reasoning may be used to
determine the value of this delay on residential gateways.
Media Gateway Controllers are typically dimensioned to handle the
peak hour traffic load, during which, in average, 10% of the lines
will be busy, placing calls whose average duration is typically 3
minutes. The processing of a call typically involves 5 to 6 Media
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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.
A security mechanism is clearly needed to prevent unauthorized
entities from using the protocol defined in this document for setting
up unauthorized calls or interfering with authorized calls. The
security mechanism for the protocol when transported over IP networks
is IPsec [RFC2401 to RFC2411].
The AH header [RFC2402] affords data origin authentication,
connectionless integrity and optional anti-replay protection of
messages passed between the MG and the MGC. The ESP header [RFC2406]
provides confidentiality of messages, if desired. For instance, the
ESP encryption service should be requested if the session
descriptions are used to carry session keys, as defined in SDP.
Implementations of the protocol defined in this document employing
the ESP header SHALL comply with section 5 of [RFC2406], which
defines a minimum set of algorithms for integrity checking and
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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.
Implementation of IPsec requires that the AH or ESP header be
inserted immediately after the IP header. This cannot be easily done
at the application level. Therefore, this presents a deployment
problem for the protocol defined in this document where the
underlying network implementation does not support IPsec.
As an interim solution, an optional AH header is defined within the
H.248 protocol header. The header fields are exactly those of the
SPI, SEQUENCE NUMBER and DATA fields as defined in [RFC2402]. The
semantics of the header fields are the same as the "transport mode"
of [RFC2402], except for the calculation of the Integrity Check value
(ICV). In IPsec, the ICV is calculated over the entire IP packet
including the IP header. This prevents spoofing of the IP addresses.
To retain the same functionality, the ICV calculation should be
performed across the entire transaction prepended by a synthesized IP
header consisting of a 32 bit source IP address, a 32 bit destination
address and an 16 bit UDP encoded as 10 hex digits. When the interim
AH mechanism is employed when TCP is the transport Layer, the UDP
Port above becomes the TCP port, and all other operations are the
same.
Implementations of the H.248 protocol SHALL implement IPsec where the
underlying operating system and the transport network supports IPsec.
Implementations of the protocol using IPv4 SHALL implement the
interim AH scheme. However, this interim scheme SHALL NOT be used
when the underlying network layer supports IPsec. IPv6
implementations are assumed to support IPsec and SHALL NOT use the
interim AH scheme.
All implementations of the interim AH mechanism SHALL comply with
section 5 of [RFC2402] which defines a minimum set of algorithms for
integrity checking using manual keys.
The interim AH interim scheme does not provide protection against
eavesdropping; thus forbidding third parties from monitoring the
connections set up by a given termination. Also, it does not provide
protection against replay attacks. These procedures do not
necessarily protect against denial of service attacks by misbehaving
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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.
The protocol allows the MGC to provide MGs with "session keys" that
can be used to encrypt the audio messages, protecting against
eavesdropping.
A specific problem of packet networks is "uncontrolled barge-in".
This attack can be performed by directing media packets to the IP
address and UDP port used by a connection. If no protection is
implemented, the packets must be decompressed and the signals must be
played on the "line side".
A basic protection against this attack is to only accept packets from
known sources, checking for example that the IP source address and
UDP source port match the values announced in the Remote Descriptor.
This has two inconveniences: it slows down connection establishment
and it can be fooled by source spoofing:
. To enable the address-based protection, the MGC must obtain the
remote session description of the egress MG and pass it to the
ingress MG. This requires at least one network roundtrip, and
leaves us with a dilemma: either allow the call to proceed
without waiting for the round trip to complete, and risk for
example, "clipping" a remote announcement, or wait for the full
roundtrip and settle for slower call-set-up procedures.
. Source spoofing is only effective if the attacker can obtain
valid pairs of source destination addresses and ports, for
example by listening to a fraction of the traffic. To fight
source spoofing, one could try to control all access points to
the network. But this is in practice very hard to achieve.
An alternative to checking the source address is to encrypt and
authenticate the packets, using a secret key that is conveyed during
the call set-up procedure. This will not slow down the call set-up,
and provides strong protection against address spoofing.
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
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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.
A physical Media Gateway may be partitioned into one or more Virtual
MGs. A virtual MG consists of a set of statically partitioned
physical Terminations and/or sets of ephemeral Terminations. A
physical Termination is controlled by one MGC. The model does not
require that other resources be statically allocated, just
Terminations. The mechanism for allocating Terminations to virtual
MGs is a management method outside the scope of the protocol. Each
of the virtual MGs appears to the MGC as a complete MG client.
A physical MG may have only one network interface, which must be
shared across virtual MGs. In such a case, the packet/cell side
Termination is shared. It should be noted however, that in use, such
interfaces require an ephemeral instance of the Termination to be
created per flow, and thus sharing the Termination is
straightforward. This mechanism does lead to a complication, namely
that the MG must always know which of its controlling MGCs should be
notified if an event occurs on the interface.
In normal operation, the Virtual MG will be instructed by the MGC to
create network flows (if it is the originating side), or to expect
flow requests (if it is the terminating side), and no confusion will
arise. However, if an unexpected event occurs, the Virtual MG must
know what to do with respect to the physical resources it is
controlling.
If recovering from the event requires manipulation of a physical
interface's state, only one MGC should do so. These issues are
resolved by allowing any of the MGCs to create EventsDescriptors to
be notified of such events, but only one MGC can have read/write
access to the physical interface properties; all other MGCs have
read-only access. The management mechanism is used to designate
which MGC has read/write capability, and is designated the Master
MGC.
Each virtual MG has its own Root Termination. In most cases the
values for the properties of the Root Termination are independently
settable by each MGC. Where there can only be one value, the
parameter is read-only to all but the Master MGC.
ServiceChange may only be applied to a Termination or set of
Terminations partitioned to the Virtual MG or created (in the case of
ephemeral Terminations) by that Virtual MG.
Cuervo, et al. Standards Track [Page 67]
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A MG is pre-provisioned by a management mechanism outside the scope
of this protocol with a Primary and (optionally) an ordered list of
Secondary MGCs. Upon a cold start of the MG, it will issue a
ServiceChange command with a "Restart" method, on the Root
Termination to its primary MGC. If the MGC accepts the MG, it will
send a Transaction Accept, with the ServiceChangeMgcId set to itself.
If the MG receives an ServiceChangeMgcId not equal to the MGC it
contacted, it sends a ServiceChange to the MGC specified in the
ServiceChangeMgcId. It continues this process until it gets a
controlling MGC to accept its registration, or it fails to get a
reply. Upon failure to obtain a reply, either from the Primary MGC,
or a designated successor, the MG tries its pre-provisioned Secondary
MGCs, in order. If the MG is unable to comply and it has established
a transport connection to the MGC, it should close that connection.
In any event, it should reject all subsequent requests from the MGC
with Error 406 Version Not Supported.
It is possible that the reply to a ServiceChange with Restart will be
lost, and a command will be received by the MG prior to the receipt
of the ServiceChange response. The MG shall issue error 505 -
Command Received before Restart Response.
The first ServiceChange command from an MG shall contain the version
number of the protocol supported by the MG in the
ServiceChangeVersion parameter. Upon receiving such a message, if the
MGC supports only a lower version, then the MGC shall send a
ServiceChangeReply with the lower version and thereafter all the
messages between MG and MGC shall conform to the lower version of the
protocol. If the MG is unable to comply and it has established a
transport connection to the MGC, it should close that connection. In
any event, it should reject all subsequent requests from the MGC with
Error 406 Version Not supported.
If the MGC supports a higher version than the MG but is able to
support the lower version proposed by the MG, it shall send a
ServiceChangeReply with the lower version and thereafter all the
messages between MG and MGC shall conform to the lower version of the
protocol. If the MGC is unable to comply, it shall reject the
association, with Error 406 Version Not Supported.
Protocol version negotiation may also occur at "handoff" and
"failover" ServiceChanges.
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When extending the protocol with new versions, the following rules
should be followed.
1. Existing protocol elements, i.e., procedures, parameters,
descriptor, property, values, should not be changed unless a
protocol error needs to be corrected or it becomes necessary to
change the operation of the service that is being supported by the
protocol.
2. The semantics of a command, a parameter, descriptor, property,
value should not be changed.
3. Established rules for formatting and encoding messages and
parameters should not be modified.
4. When information elements are found to be obsolete they can be
marked as not used. However, the identifier for that information
element will be marked as reserved. In that way it can not be used
in future versions.
If a MG fails, but is capable of sending a message to the MGC, it
sends a ServiceChange with an appropriate method (graceful or forced)
and specifies the Root TerminationID. When it returns to service, it
sends a ServiceChange with a "Restart" method.
Allowing the MGC to send duplicate messages to both MGs accommodates
pairs of MGs that are capable of redundant failover of one of the
MGs. Only the Working MG shall accept or reject transactions. Upon
failover, the Primary MG sends a ServiceChange command with a
"Failover" method and a "MG Impending Failure" reason. The MGC then
uses the primary MG as the active MG. When the error condition is
repaired, the Working MG can send a "ServiceChange" with a "Restart"
method.
If the MG detects a failure of its controlling MGC, it attempts to
contact the next MGC on its pre-provisioned list. It starts its
attempts at the beginning (Primary MGC), unless that was the MGC that
failed, in which case it starts at its first Secondary MGC. It sends
a ServiceChange message with a "Failover" method and a " MGC
Impending Failure" reason.
In partial failure, or manual maintenance reasons, an MGC may wish to
direct its controlled MGs to use a different MGC. To do so, it sends
a ServiceChange method to the MG with a "HandOff" method, and its
Cuervo, et al. Standards Track [Page 69]
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designated replacement in ServiceChangeMgcId. The MG should send a
ServiceChange message with a "Handoff" method and a "MGC directed
change" reason to the designated MGC. If it fails to get a reply, or
fails to see an Audit command subsequently, it should behave as if
its MGC failed, and start contacting secondary MGCs. If the MG is
unable to establish a control relationship with any MGC, it shall
wait a random amount of time as described in section 9.2 and then
start contacting its primary, and if necessary, its secondary MGCs
again.
No recommendation is made on how the MGCs involved in the Handoff
maintain state information; this is considered to be out of scope of
this recommendation. The MGC and MG may take the following steps when
Handoff occurs. When the MGC initiates a HandOff, the handover
should be transparent to Operations on the Media Gateway.
Transactions can be executed in any order, and could be in progress
when the ServiceChange is executed. Accordingly, commands in
progress continue, transaction replies are sent to the new MGC (after
a new control association is established), and the MG should expect
outstanding transaction replies from the new MGC. No new messages
shall be sent to the new MGC until the control association is
established. Repeated transaction requests shall be directed to the
new MGC. The MG shall maintain state on all terminations and
contexts.
It is possible that the MGC could be implemented in such a way that a
failed MGC is replaced by a working MGC where the identity of the new
MGC is the same as the failed one. In such a case,
ServiceChangeMgcId would be specified with the previous value and the
MG shall behave as if the value was changed, and send a ServiceChange
message, as above.
Pairs of MGCs that are capable of redundant failover can notify the
controlled MGs of the failover by the above mechanism.
The primary mechanism for extension is by means of Packages.
Packages define additional Properties, Events, Signals and Statistics
that may occur on Terminations.
Packages defined by IETF will appear in separate RFCs.
Packages defined by ITU-T may appear in the relevant recommendations
(e.g. as annexes).
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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.
Packages define Properties, Events, Signals, and Statistics.
Packages may also define new error codes according to the guidelines
given in section 13.2. This is a matter of documentary convenience:
the package documentation is submitted to IANA in support of the
error code registration. If a package is modified, it is unnecessary
to provide IANA with a new document reference in support of the error
code unless the description of the error code itself is modified.
Names of all such defined constructs shall consist of the PackageID
(which uniquely identifies the package) and the ID of the item (which
uniquely identifies the item in that package). In the text encoding
the two shall be separated by a forward slash ("/") character.
Example: togen/playtone is the text encoding to refer to the play
tone signal in the tone generation package.
A Package will contain the following sections:
Overall description of the package, specifying:
. Package Name: only descriptive,
. PackageID: Is an identifier
. Description:
. Version: A new version of a package can only add additional
Properties, Events, Signals, Statistics and new possible values
for an existing parameter described in the original package. No
deletions or modifications shall be allowed. A version is an
integer in the range from 1 to 99.
. Extends (Optional): A package may extend an existing package. The
version of the original package must be specified. When a package
extends another package it shall only add additional Properties,
Events, Signals, Statistics and new possible values for an
Cuervo, et al. Standards Track [Page 71]
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existing parameter described in the original package. An extended
package shall not redefine or overload a name defined in the
original package. Hence, if package B version 1 extends package A
version 1, version 2 of B will not be able to extend the A version
2 if A version 2 defines a name already in B version 1.
Properties defined by the package, specifying:
. Property Name: only descriptive.
. PropertyID: Is an identifier
. Description:
. Type: One of:
String: UTF-8 string
Integer: 4 byte signed integer
Double: 8 byte signed integer
Character: Unicode UTF-8 encoding of a single letter.
Could be more than one octet.
Enumeration: One of a list of possible unique values (See 12.3)
Sub-list: A list of several values from a list
Boolean
. Possible Values:
. Defined in: Which H.248 descriptor the property is defined in.
LocalControl is for stream dependent properties. TerminationState
is for stream independent properties.
. Characteristics: Read / Write or both, and (optionally), global:
Indicates whether a property is read-only, or read-write, and if
it is global. If Global is omitted, the property is not global.
If a property is declared as global, the value of the property is
shared by all terminations realizing the package.
Events defined by the package, specifying:
. Event name: only descriptive.
. EventID: Is an identifier
. Description:
. EventsDescriptor Parameters: Parameters used by the MGC to
configure the event, and found in the EventsDescriptor. See
section 12.2.
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. ObservedEventsDescriptor Parameters: Parameters returned to the
MGC in Notify requests and in replies to command requests from
the MGC that audit ObservedEventsDescriptor, and found in the
ObservedEventsDescriptor. See section 12.2.
. Signals defined by the package, specifying:
. Signal Name: only descriptive.
. SignalID: Is an identifier. SignalID is used in a
SignalsDescriptor
. Description
. SignalType: One of:
- OO (On/Off)
- TO (TimeOut)
- BR (Brief)
Note - SignalType may be defined such that it is dependent on the
value of one or more parameters. Signals that would be played with
SignalType BR should have a default duration. The package has to
define the default duration and signalType.
. Duration: in hundredths of seconds
. Additional Parameters: See section 12.2
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.
Events and Signals.
. Parameter Name: only descriptive
. ParameterID: Is an identifier
. Type: One of:
String: UTF-8 octet string
Integer: 4 octet signed integer
Double: 8 octet signed integer
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Character: Unicode UTF-8 encoding of a single letter. Could be
more than one octet.
Enumeration: One of a list of possible unique values (See 12.3)
Sub-list: A list of several values from a list
Boolean
. Possible values:
. Description:
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.
Identifiers in text encoding shall be strings of up to 64 characters,
containing no spaces, starting with an alphanumeric character and
consisting of alphanumeric characters and / or digits, and possibly
including the special character underscore ("_").
Identifiers in binary encoding are 2 octets long.
Both text and binary values shall be specified for each identifier,
including identifiers used as values in enumerated types.
The following considerations SHALL be met to register a package with
IANA:
1. A unique string name, unique serial number and version number is
registered for each package. The string name is used with text
encoding. The serial number shall be used with binary encoding.
Serial Numbers 60000-64565 are reserved for private use. Serial
number 0 is reserved.
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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
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.
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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.
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RFC 2885 Megaco Protocol August 2000
ANNEX A: BINARY ENCODING OF THE PROTOCOL (NORMATIVE)
This Annex specifies the syntax of messages using the notation
defined in ASN.1 [ITU-T Recommendation X.680 (1997): Information
Technology - Abstract Syntax Notation One (ASN.1) - Specification of
basic notation.]. Messages shall be encoded for transmission by
applying the basic encoding rules specified in [ITU-T Recommendation
X.690(1994) Information Technology - ASN.1 Encoding Rules:
Specification of Basic Encoding Rules (BER)].
The use of wildcards ALL and CHOOSE is allowed in the protocol. This
allows a MGC to partially specify Termination IDs and let the MG
choose from the values that conform to the partial specification.
Termination IDs may encode a hierarchy of names. This hierarchy is
provisioned. For instance, a TerminationID may consist of a trunk
group, a trunk within the group and a circuit. Wildcarding must be
possible at all levels. The following paragraphs explain how this is
achieved.
The ASN.1 description uses octet strings of up to 8 octets in length
for Termination IDs. This means that Termination IDs consist of at
most 64 bits. A fully specified Termination ID may be preceded by a
sequence of wildcarding fields. A wildcarding field is octet in
length. Bit 7 (the most significant bit) of this octet specifies
what type of wildcarding is invoked: if the bit value equals 1, then
the ALL wildcard is used; if the bit value if 0, then the CHOOSE
wildcard is used. Bit 6 of the wildcarding field specifies whether
the wildcarding pertains to one level in the hierarchical naming
scheme (bit value 0) or to the level of the hierarchy specified in
the wildcarding field plus all lower levels (bit value 1). Bits 0
through 5 of the wildcarding field specify the bit position in the
Termination ID at which the starts.
We illustrate this scheme with some examples. In these examples, the
most significant bit in a string of bits appears on the left hand
side.
Assume that Termination IDs are three octets long and that each octet
represents a level in a hierarchical naming scheme. A valid
Termination ID is
00000001 00011110 01010101.
Addressing ALL names with prefix 00000001 00011110 is done as
follows:
wildcarding field: 10000111
Termination ID: 00000001 00011110 xxxxxxxx.
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The values of the bits labeled "x" is irrelevant and shall be ignored
by the receiver.
Indicating to the receiver that is must choose a name with 00011110
as the second octet is done as follows:
wildcarding fields: 00010111 followed by 00000111
Termination ID: xxxxxxxx 00011110 xxxxxxxx.
The first wildcard field indicates a CHOOSE wildcard for the level in
the naming hierarchy starting at bit 23, the highest level in our
assumed naming scheme. The second wildcard field indicates a CHOOSE
wildcard for the level in the naming hierarchy starting at bit 7, the
lowest level in our assumed naming scheme.
Finally, a CHOOSE-wildcarded name with the highest level of the name
equal to 00000001 is specified as follows:
wildcard field: 01001111
Termination ID: 0000001 xxxxxxxx xxxxxxxx .
Bit value 1 at bit position 6 of the first octet of the wildcard
field indicates that the wildcarding pertains to the specified level
in the naming hierarchy and all lower levels.
Context IDs may also be wildcarded. In the case of Context IDs,
however, specifying partial names is not allowed. Context ID 0x0
SHALL be used to indicate the NULL Context, Context ID 0xFFFFFFFE
SHALL be used to indicate a CHOOSE wildcard, and Context ID
0xFFFFFFFF SHALL be used to indicate an ALL wildcard.
TerminationID 0xFFFFFFFFFFFFFFFF SHALL be used to indicate the ROOT
Termination.
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.
PropertyID Property Type Value
Tag
Media 1001 Enumeration Audio(0), Video(1),
Data(2),
Transmission mode 1002 Enumeration Send(0), Receive(1),
Send&Receive(2)
Number of Channels 1003 Unsigned 0-255
Integer
Sampling rate 1004 Unsigned 0-2^32
Integer
Bitrate 1005 Integer (0..4294967295)
Note - units of 100 bit/s
Cuervo, et al. Standards Track [Page 107]
RFC 2885 Megaco Protocol August 2000
ACodec 1006 Octet String Audio Codec Type:
Reference: ITU-T Rec. Q.765 - Application transport mechanism.
Non-ITU codecs are defined with the appropriate standards
organisation under a defined Organizational Identifier.
Samplepp 1007 Unsigned Maximum samples or
Integer frames per packet: 0-
65535
Silencesupp 1008 BOOLEAN Silence Suppression:
True/false
Encrypttype 1009 Octet string Ref.: rec. H.245
Encryptkey 100A Octet string Encryption key
SIZE(0..65535)
Ref.: rec. H.235
Echocanc 100B Enumeration Echo Canceller:
Off(0), G.165(1),
G168(2)
Gain 100C Unsigned Gain in db: 0-65535
Integer
Jitterbuff 100D Unsigned Jitter buffer size in
Integer ms: 0-65535
PropDelay 100E Unsigned Propagation Delay:
Integer 0..65535
Maximum propagation delay in milliseconds for the bearer
connection between two media gateways. The maximum delay will be
dependent on the bearer technology.
RTPpayload 100F integer Payload type in RTP
Profile for Audio and
Video Conferences
with Minimal Control
Ref.: RFC 1890
PropertyID Property Type Value
Tag
Mediatx 3001 Enumeration Media Transport Type:
TDM Circuit(0), ATM(1),
FR(2), Ipv4(3), Ipv6(4),
_
BIR 3002 4 OCTET Value depends on
transport technology
NSAP 3003 1-20 OCTETS See NSAP
Reference: ITU X.213 Annex A
PropertyID Property Type Value
Tag
DLCI 5001 Unsigned Integer Data link connection
id
CID 5002 Unsigned Integer sub-channel id.
SID/Noiselevel 5003 Unsigned Integer silence insertion
descriptor
Primary Payload 5004 Unsigned Integer Primary Payload Type
type
Covers FAX and codecs
Cuervo, et al. Standards Track [Page 112]
RFC 2885 Megaco Protocol August 2000
PropertyID Property Type Value
Tag
AESA 7001 20 OCTETS AAL2 service endpoint
address
as defined in Reference: ITU Recommendation Q.2630.1
ESEA
NSEA
BIR See C.3 4 OCTETS Served user generated
reference
as defined in Reference: ITU Recommendation Q.2630.1
SUGR
ALC 7002 12 OCTETS AAL2 link
characteristics
as defined in Reference: ITU Recommendation Q.2630.1
max/average CPS-SDU bitrate,
max/average CPS-SDU size
SSCS 7003 I.366.2: Service
audio (8 OCTETS) specific
multirate (3 OCTETS) convergence
or I.366.1: sublayer
SAR-assured (14 OCTETS)/ information
unassured (7 OCTETS)
as defined in Reference: Q.2630.1 and used in I.366.1 and I.366.2
I.366.2: audio/multirate
Cuervo, et al. Standards Track [Page 113]
RFC 2885 Megaco Protocol August 2000
I.366.1: SAR-assured/unassured
SUT 7004 1..254 octets Served user transport
parameter
as defined in Reference: ITU Recommendation Q.2630.1
TCI 7005 BOOLEAN Test connection
indicator
as defined in Reference: ITU Recommendation Q.2630.1
Timer_CU 7006 32 bit integer Timer-CU: Milliseconds
to hold partially
filled cell before
sending.
MaxCPSSDU 7007 8 bit integer Maximum Common Part
Sublayer Service Data
Unit
Ref.: rec. Q.2630.1
SCLP 7008 Boolean Set Cell Local
PriorityLP bit:
True if CLP bit is to
be set
EETR 7009 Boolean Timing Requirements
Reference: ITU Recommendation Q.2931 (1995)
End to End Timing Required:
In broadband bearer capability
CID 700A 8 bits subchannel id, 0-255
Ref.: rec. I.363.2 (09/97)
PropertyID Property Type Value
Tag
FMSDU A001 32 bit integer Forward Maximum CPCS-
SDU Size:
Reference: ITU Recommendation Q.2931 (1995)
Maximum CPCS-SDU size sent in the direction from the calling user
to the called user.
BMSDU A002 32 bit integer Backwards Maximum
CPCS-SDU Size
Reference: ITU Recommendation Q.2931 (1995)
Maximum CPCS-SDU size sent in the direction from the called user
to the calling user.
SSCS See See table C.7 See table C.7
table
C.7
Additional values:
VPI/VCI
SC See See Table C.4 See table C.4
Table
C.4
Cuervo, et al. Standards Track [Page 123]
RFC 2885 Megaco Protocol August 2000
PropertyID Property Type Value
Tag
SDP_V B001 STRING Protocol Version
SDP_O B002 STRING Owner/creator and
session ID
SDP_S B003 STRING Sesson name
SDP_I B004 STRING Session identifier
SDP_U B005 STRING URI of descriptor
SDC_E B006 STRING email address
SDP_P B007 STRING phone number
SDP_C B008 STRING Connection information
SDP_B B009 STRING Bandwidth Information
SDP_Z B00A STRING time zone adjustment
SDP_K B00B STRING Encryption Key
SDP_A B00C STRING Zero or more session
attributes
SDP_T B00D STRING Active Session Time
SDP_R B00E STRING Zero or more repeat
times
Reference in all cases: IETF RFC2327, "Session Description
Protocol"
PropertyID Property Type Value
Tag
OLC C001 octet string The value of H.245
OpenLogicalChannel
structure.
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OLCack C002 octet string The value of H.245
OpenLogicalChannelAck
structure.
OLCcnf C003 octet string The value of H.245
OpenLogicalChannelConfirm
structure.
OLCrej C004 octet string The value of H.245
OpenLogicalChannelReject
structure.
CLC C005 octet string The value of H.245
CloseLogicalChannel
structure.
CLCack C006 octet string The value of H.245
CloseLogicalChannelAck
structure.
Reference in all cases: ITU-T Recommendation H.245
ANNEX D TRANSPORT OVER IP (NORMATIVE)
Protocol messages defined in this document may be transmitted over
UDP. When no port is provided by the peer (see section 7.2.8),
commands should be sent to the default port number, 2944 for text-
encoded operation or 2945 for binary-encoded operation. Responses
must be sent to the address and port from which the corresponding
commands were sent except if the response is to a handoff or
failover, in which case the procedures of 11.5 apply.
Implementors using IP/UDP with ALF should be aware of the
restrictions of the MTU on the maximum message size.
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
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compared to the list of currently outstanding transactions. If a
match is found in that list, indicating a duplicate transaction, the
entity does not execute the transaction (see section 8.2.3 for
procedures on sending TransactionPending).
The procedure uses a long timer value, noted LONG-TIMER in the
following. The timer should be set larger than the maximum duration
of a transaction, which should take into account the maximum number
of repetitions, the maximum value of the repetition timer and the
maximum propagation delay of a packet in the network. A suggested
value is 30 seconds.
The copy of the responses may be destroyed either LONG-TIMER seconds
after the response is issued, or when the entity receives a
confirmation that the response has been received, through the
"Response Acknowledgement parameter". For transactions that are
acknowledged through this parameter, the entity shall keep a copy of
the transaction-id for LONG-TIMER seconds after the response is
issued, in order to detect and ignore duplicate copies of the
transaction request that could be produced by the network.
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.
The TransactionResponse Acknowledgement parameter can be found in any
message. It carries a set of "confirmed transaction-id ranges".
Entities may choose to delete the copies of the responses to
transactions whose id is included in "confirmed transaction-id
Cuervo, et al. Standards Track [Page 126]
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ranges" received in the transaction response messages. They should
silently discard further commands when the transaction-id falls
within these ranges.
The "confirmed transaction-id ranges" values shall not be used if
more than LONG-TIMER seconds have elapsed since the MG issued its
last response to that MGC, or when a MG resumes operation. In this
situation, transactions should be accepted and processed, without any
test on the transaction-id.
Messages that carry the "Transaction Response Acknowledgement"
parameter may be transmitted in any order. The entity shall retain
the "confirmed transaction-id ranges" receivedfor LONG-TIMER seconds.
In the binary encoding, if only the firstAck is present in a response
acknowledgement (see Annex A.2), only one transaction is
acknowledged. If both firstAck and lastAck are present, then the
range of transactions from firstAck to lastAck is acknowledged. In
the text encoding, a horizontal dash is used to indicate a range of
transactions being acknowledged (see Annex B.2).
It is the responsibility of the requesting entity to provide suitable
time outs for all outstanding transactions, and to retry transactions
when time outs have been exceeded. Furthermore, when repeated
transactions fail to be acknowledged, it is the responsibility of the
requesting entity to seek redundant services and/or clear existing or
pending connections.
The specification purposely avoids specifying any value for the
retransmission timers. These values are typically network dependent.
The retransmission timers should normally estimate the timer value by
measuring the time spent between the sending of a command and the
return of a response.
Note - One possibility is to use the algorithm implemented in TCP-
IP, which uses two variables:
. The average acknowledgement delay, AAD, estimated through an
exponentially smoothed average of the observed delays.
. The average deviation, ADEV, estimated through an exponentially
smoothed average of the absolute value of the difference between
the observed delay and the current average. The retransmission
timer, in TCP, is set to the sum of the average delay plus N
times the average deviation. The maximum value of the timer
should however be bounded for the protocol defined in this
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document, in order to guarantee that no repeated packet would be
received by the gateways after LONG-TIMER seconds. A suggested
maximum value is 4 seconds.
After any retransmission, the entity should do the following:
. It should double the estimated value of the average delay, AAD
. It should compute a random value, uniformly distributed between
0.5 AAD and AAD
. It should set the retransmission timer to the sum of that random
value and N times the average deviation.
This procedure has two effects. Because it includes an exponentially
increasing component, it will automatically slow down the stream of
messages in case of congestion. Because it includes a random
component, it will break the potential synchronization between
notifications triggered by the same external event.
Executing some transactions may require a long time. Long execution
times may interact with the timer based retransmission procedure.
This may result either in an inordinate number of retransmissions, or
in timer values that become too long to be efficient. Entities that
can predict that a transaction will require a long execution time may
send a provisional response, "Transaction Pending".
Entities that receive a Transaction Pending shall switch to a
different repetition timer for repeating requests. The root
termination has a property (ProvisionalResponseTimerValue), which can
be set to the requested maximum number of milliseconds between
receipt of a command and transmission of the TransactionPending
response. Upon receipt of a final response, an immediate
confirmation shall be sent, and normal repetition timers shall be
used thereafter. Receipt of a Transaction Pending after receipt of a
reply shall be ignored.
The protocol is organized as a set of transactions, each of which is
composed request and a response, commonly referred to as an
acknowledgement. The protocol messages, being carried over UDP, may
be subject to losses. In the absence of a timely response,
transactions are repeated. Entities are expected to keep in memory a
Cuervo, et al. Standards Track [Page 128]
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list of the responses that they sent to recent transactions, i.e. a
list of all the responses they sent over the last LONG-TIMER seconds,
and a list of the transactions that are currently being executed.
The repetition mechanism is used to guard against three types of
possible errors:
. transmission errors, when for example a packet is lost due to
noise on a line or congestion in a queue;
. component failure, when for example an interface to a entity
becomes unavailable;
. entity failure, when for example an entire entity become
unavailable.
The entities should be able to derive from the past history an
estimate of the packet loss rate due to transmission errors. In a
properly configured system, this loss rate should be kept very low,
typically less than 1%. If a Media Gateway Controller or a Media
Gateway has to repeat a message more than a few times, it is very
legitimate to assume that something else than a transmission error is
occurring. For example, given a loss rate of 1%, the probability
that five consecutive transmission attempts fail is 1 in 100 billion,
an event that should occur less than once every 10 days for a Media
Gateway Controller that processes 1 000 transactions per second.
(Indeed, the number of repetition that is considered excessive should
be a function of the prevailing packet loss rate.) We should note
that the "suspicion threshold", which we will call "Max1", is
normally lower than the "disconnection threshold", which should be
set to a larger value.
A classic retransmission algorithm would simply count the number of
successive repetitions, and conclude that the association is broken
after retransmitting the packet an excessive number of times
(typically between 7 and 11 times.) In order to account for the
possibility of an undetected or in-progress "failover", we modify the
classic algorithm so that if the Media Gateway receives a valid
ServiceChange message announcing a failover, it will start
transmitting outstanding commands to that new MGC. Responses to
commands are still transmitted to the source address of the command.
In order to automatically adapt to network load, this document
specifies exponentially increasing timers. If the initial timer is
set to 200 milliseconds, the loss of a fifth retransmission will be
detected after about 6 seconds. This is probably an acceptable
waiting delay to detect a failover. The repetitions should continue
after that delay not only in order to perhaps overcome a transient
Cuervo, et al. Standards Track [Page 129]
RFC 2885 Megaco Protocol August 2000
connectivity problem, but also in order to allow some more time for
the execution of a failover - waiting a total delay of 30 seconds is
probably acceptable.
It is, however, important that the maximum delay of retransmissions
be bounded. Prior to any retransmission, it is checked that the time
elapsed since the sending of the initial datagram is no greater than
T-MAX. If more than T-MAX time has elapsed, the MG concludes that the
MGC has failed, and it begins its recovery process. When the MG
establishes a new control association, it can retransmit to the new
MGC. Alternatively, a MG may use a ServiceChange with
ServiceChangeMethod equal to disconnected to inform the new MGC that
the MG lost one or more transactions. The value T-MAX is related to
the LONG-TIMER value: the LONG-TIMER value is obtained by adding to
T-MAX the maximum propagation delay in the network.
Protocol messages as defined in this document may be transmitted over
TCP. When no port is specified by the other side (see section
7.2.8), the commands should be sent to the default port. The defined
protocol has messages as the unit of transfer, while TCP is a
stream-oriented protocol. TPKT, according to RFC1006 SHALL be used
to delineate messages within the TCP stream.
In a transaction-oriented protocol, there are still ways for
transaction requests or responses to be lost. As such, it is
recommended that entities using TCP transport implement application
level timers for each request and each response, similar to those
specified for application level framing over UDP.
Messages, being carried over TCP, are not subject to transport
losses, but loss of a transaction request or its reply may
nonetheless be noted in real implementations. In the absence of a
timely response, commands are repeated. Most commands are not
idempotent. The state of the MG would become unpredictable if, for
example, Add commands were executed several times.
To guard against such losses, it is recommended that entities follow
the procedures in section D.1.1
For the same reasons, it is possible that transaction replies may be
lost even with a reliable delivery protocol such as TCP. It is
recommended that entities follow the procedures in section D.1.2.2.
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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.
As with UDP, executing some transactions may require a long time.
Entities that can predict that a transaction will require a long
execution time may send a provisional response, "Transaction
Pending". They should send this response if they receive a repetition
of a transaction that is still being executed.
Entities that receive a Transaction Pending shall switch to a longer
repetition timer for that transaction.
Entities shall retain Transactions and replies until they are
confirmed. The basic procedure of section D.1.4 should be followed,
but simple timer values should be sufficient. There is no need to
send an immediate confirmation upon receipt of a final response.
TCP provides ordered delivery of transactions. No special procedures
are required. It should be noted that ALF/UDP allows sending entity
to modify its behavior under congestion, and in particular, could
reorder transactions when congestion is encountered. TCP could not
achieve the same results.
ANNEX E BASIC PACKAGES
This Annex contains definitions of some packages for use with the
Megaco protocol.
Cause
-----
EventID: cause (0x0001)
Generic error event
ObservedEvents Descriptor Parameters:
General Cause
-------------
ParameterID: Generalcause (0x0001)
Description: This parameter groups the failures into six
groups, which the MGC may act upon.
Possible values: Enumerated,
"NR" Normal Release (0x0001)
"UR" Unavailable Resources (0x0002)
"FT" Failure, Temporary (0x0003)
"FP" Failure, Permanent (0x0004)
"IW" Interworking Error (0x0005)
"UN" Unsupported (0x0006)
Failure Cause
-------------
ParameterID: Failurecause (0x0002)
Description: The Release Cause is the value generated by the
Released equipment, i.e. a released network connection.
The concerned value is defined in the appropriate bearer
control protocol.
Possible Values: OCTET STRING
Signal Completion
-----------------
EventID: sc (0x0002)
Indicates termination of one or more signals for which the
notifyCompletion parameter was set to "ON". For further procedural
description, see sections 7.1.11, 7.1.17, and 7.2.7.
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ObservedEvents Descriptor parameters:
Signal Identity
---------------
ParameterID: SigID (0x0001)
This parameter identifies the signals which have terminated.
Type: list
Possible values: a list of signals and/or sequential signal
lists which have terminated. A signal outside of a sequential
signal list shall be identified using the pkgdName syntax
without wildcarding. An individual signal inside of a
sequential signal list shall be identified using the sequential
signal list syntax with the correct signal list identifier,
enclosing the name of the specific signal which terminated in
pkgdName syntax.
Termination Method
------------------
ParameterID: Meth (0x0002)
Indicates the means by which the signal terminated.
Type: enumeration
Possible values:
"TO" (0x0001) Duration expired
"EV" (0x0002) Interrupted by event
"SD" (0x0003) Halted by new Signals Descriptor
"NC" (0x0004) Not completed, other cause
MaxNrOfContexts
---------------
PropertyID: maxNumberOfContexts (0x0001)
The value of this property gives the maximum number of contexts that
can exist at any time. The NULL context is not included in this
number.
Type: Double
Possible values: 1 and up
MaxTerminationsPerContext
-------------------------
PropertyID: maxTerminationsPerContext (0x0002)
The maximum number of allowed terminations in a context, see section
6.1
Type: Integer
Possible Values: any integer
Defined In: TerminationState
normalMGExecutionTime
---------------------
PropertyId: normalMGExecutionTime (0x0003)
Settable by the MGC to indicate the interval within which the MGC
expects a response to any transaction from the MG (exclusive of
network delay)
Type: Integer
Possible Values: any integer, represents milliseconds
normalMGCExecutionTime
----------------------
PropertyId: normalMGCExecutionTime (0x0004)
Settable by the MGC to indicate the interval within which the MG
should expects a response to any transaction from the MGC (exclusive
of network delay)
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Type: Integer
Possible Values: any integer, represents milliseconds
ProvisionalResponseTimerValue
-----------------------------
PropertyId: ProvisionalResponseTimerValue (0x0005)
Indicates the time within which to expect a Pending Response if a
Transaction cannot be completed. Initially set to
normalMGExecutionTime or normalMGCExecutionTime as appropriate, plus
network delay, but may be lowered.
PackageID: tonegen (0x0001)
Version: 1
Extends: None
Description:
This package defines signals to generate audio tones. This package
does not specify parameter values. It is intended to be extendable.
Generally, tones are defined as an individual signal with a
parameter, ind, representing "interdigit" time delay, and a tone id
to be used with playtones. A tone id should be kept consistent with
any tone generation for the same tone. MGs are expected to be
provisioned with the characteristics of appropriate tones for the
country in which the MG is located.
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.
PackageID: tonedet (0x0002)
Version: 1
Extends: None
This Package defines events for audio tone detection. Tones are
selected by name (tone id). MGs are expected to be provisioned with
the characteristics of appropriate tones for the country in which the
MG is located.
This package does not specify parameter values. It is intended to be
extendable.
Start tone detected
-------------------
EventID: std, 0x0001
Detects the start of a tone. The characteristics of positive tone
detection is implementation dependent.
EventsDescriptor parameters:
Tone id list
------------
ParameterID: tl (0x0001)
Type: list of tone ids
Possible values: The only tone id defined in this package is
"wild card" which is "*" in text encoding and 0x0000 in binary.
Extensions to this package would add possible values for tone
id. If tl is "wild card", any tone id is detected.
ObservedEventsDescriptor parameters:
Tone id
--------
ParameterID: tid (0x0003)
Type: Enumeration
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Possible values: "wildcard" as defined above is the only value
defined in this package. Extensions to this package would add
additional possible values for tone id.
End tone detected
-----------------
EventID: etd, 0x0002
Detects the end of a tone.
EventDescriptor parameters:
Tone id list
------------
ParameterID: tl (0x0001)
Type: enumeration or list of enumerated types
Possible values: No possible values are specified in this
package. Extensions to this package would add possible values
for tone id.
ObservedEventsDescriptor parameters:
Tone id
-------
ParameterID: tid (0x0003)
Type: Enumeration
Possible values: "wildcard" as defined above is the only value
defined in this package. Extensions to this package would add
possible values for tone id
Duration
--------
ParameterId: dur (0x0002)
Type: integer, in milliseconds
This parameter contains the duration of the tone from first
detection until it stopped.
Long tone detected
------------------
EventID: ltd, 0x0003
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Detects that a tone has been playing for at least a certain amount of
time
EventDescriptor parameters:
Tone id list
------------
ParameterID: tl (0x0001)
Type: enumeration or list
Possible values: "wildcard" as defined above is the only value
defined in this package. Extensions to this package would add
possible values for tone id
Duration:
---------
ParameterID: dur (0x0002)
Type: integer, duration to test against
Possible values: any legal integer, expressed in milliseconds.
ObservedEventsDescriptor parameters:
Tone id
-------
ParameterID: tid (0x0003)
Possible values: No possible values are specified in this
package. Extensions to this package would add possible values
for tone id.
PackageID: dg (0x0003) Version: 1 Extends: tonegen version 1
This package defines the basic DTMF tones as signals and extends the
allowed values of parameter tl of playtone in tonegen.
dtmf character 0
----------------
SignalID: d0 (0x0010)
Generate DTMF 0 tone. The physical characteristic of DTMF 0 is
defined in the gateway.
Signal Type: Brief
Duration: Provisioned
Additional Parameters:
None
Additional Values:
-----------------
d0 (0x0010) is defined as a toneid for playtone.
The other dtmf characters are specified in exactly the same way. A
table with all signal names and signal IDs is included. Note that
each dtmf character is defined as both a signal and a toneid, thus
extending the basic tone generation package. Also note that dtmf
SignalIds are different from the names used in a digit map.
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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)
PackageID: dd (0x0004)
Version: 1
Extends: tonedet version 1
This package defines the basic DTMF tones detection. This Package
extends the possible values of tone id in the "start tone detected"
"end tone detected" and "long tone detected" events.
Additional tone id values are all tone ids described in package dg
(basic DTMF generator package).
The following table maps DTMF events to digit map symbols as
described in section 7.1.14.
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DTMF Event Symbol
d0 "0"
d1 "1"
d2 "2"
d3 "3"
d4 "4"
d5 "5"
d6 "6"
d7 "7"
d8 "8"
d9 "9"
da "A" or "a"
db "B" or "b"
dc "C" or "c"
dd "D" or "d"
ds "E" or "e"
do "F" or "f"
DTMF digits
-----------
EventIds are defined with the same names as the SignalIds defined in
the table found in section E.5.3.
DigitMap Completion Event
-------------------------
EventID: ce, 0x0001
Generated when a digit map completes as described in section 7.1.14.
EventsDescriptor parameters: digit map processing is activated only
if a digit map parameter is present, specifying a digit map by name
or by value. Other parameters such as a KeepActive flag or embedded
Events or Signals Descriptors may be present.
ObservedEventsDescriptor parameters:
DigitString
-----------
ParameterID: ds (0x0001)
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Type: string of digit map symbols (possibly empty) returned as
a quotedString.
Possible values: a sequence of the characters "0" through "9",
"A" through "F", and the long duration modifier "L".
Description: the portion of the current dial string as
described in section 7.1.14 which matched part or all of an
alternative event sequence specified in the digit map.
Termination Method
------------------
ParameterID: Meth (0x0003)
Type: enumeration
Possible values:
"UM" (0x0001) Unambiguous match
"PM" (0x0002) Partial match, completion by timer
expiry or unmatched event
"FM" (0x0003) Full match, completion by timer expiry
or unmatched event
Description: indicates the reason for generation of the event.
See the procedures in section 7.1.14.
PackageID: cg, 0x0005
Version: 1
Extends: tonegen version 1
This package defines the basic call progress tones as signals and
extends the allowed values of the tl parameter of playtone in
tonegen.
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Dial Tone
---------
SignaID: dt (0x0030)
Generate dial tone. The physical characteristic of dial tone is
available in the gateway.
Signal Type: Timeout
Duration: Provisioned
Additional Parameters:
None
Additional Values
-----------------
dt (0x0030) is defined as a tone id for playtone The other tones of
this package are defined in exactly the same way. A table with all
signal names and signal IDs is included. Note that each tone is
defined as both a signal and a toneid, thus extending the basic tone
generation package.
Signal Name Signal ID/tone id
Dial Tone dt (0x0030)
Ringing Tone rt (0x0031)
Busy Tone bt (0x0032)
Congestion Tone ct (0x0033)
Special Information Tone sit(0x0034)
Warning Tone wt (0x0035)
Payphone Recognition Tone pt (0x0036)
Call Waiting Tone cw (0x0037)
Caller Waiting Tone cr (0x0038)
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NOTE - The required set of tone ids corresponds to those defined in
Recommendation E.180/Q.35 [ITU-T Recommendation E.180/Q.35 (1998)].
See E.180 for definition of the meanings of these tones.
PackageID: cd (0x0006)
Version: 1
Extends: tonedet version 1
This package defines the basic call progress detection tones. This
Package extends the possible values of tone id in the "start tone
detected", "end tone detected" and "long tone detected" events.
Additional values
-----------------
tone id values are defined for start tone detected, end tone detected
and long tone detected with the same values as those in package cg
(call progress tones generation package).
The required set of tone ids corresponds to Recommendation E.180/Q.35
[ITU-T Recommendation E.180/Q.35 (1998)]. See Recommendation
E.180/Q.35 for definition of the meanings of these tones.
onhook
------
EventID: on (0x0004)
Detects handset going on hook. Whenever an events descriptor is
activated that requests monitoring for an on-hook event and the line
is already on-hook, then the MG shall immediately generate an on-hook
event.
EventDescriptor parameters
None
ObservedEventsDescriptor parameters
None
offhook
-------
EventID: of (0x0005)
Detects handset going off hook. Whenever an events descriptor is
activated that requests monitoring for an off-hook event and the line
is already off-hook, then the MG shall immediately generate an off-
hook event.
EventDescriptor parameters
None
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ObservedEventsDescriptor parameters
None
flashhook
---------
EventID: fl, 0x0006
Detects handset flash. A flash occurs when an onhook is followed by
an offhook between a minimum and maximum duration.
EventDescriptor parameters
Minimum duration
----------------
ParameterID: mindur (0x0004)
Type: integer in milliseconds
Default value is provisioned
Maximum duration
----------------
ParameterID: maxdur (0x0005)
Type: integer in milliseconds
Default value is provisioned
ObservedEventsDescriptor parameters
None
ring
----
SignalID: ri, 0x0002
Applies ringing on the line
Signal Type: TimeOut
Duration: Provisioned
Additional Parameters:
Cadence
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RFC 2885 Megaco Protocol August 2000
-------
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.
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.
Continuity test
---------------
SignalID: ct (0x0003)
Initiates sending of continuity test tone on the termination to which
it is applied.
Signal Type: TimeOut
Default value is provisioned
Additional Parameters:
None
Respond
-------
SignalID: rsp (0x0004)
The signal is used to respond to a continuity test . See section
E.10.5 for further explanation.
Signal Type: TimeOut
Default duration is provisioned
Additional Parameters:
None.
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When a MGC wants to initiate a continuity test, it sends a command to
the MG containing
. a signals descriptor with the ct signal, and
. an events descriptor containing the cmp event.
Upon reception of a command containing the ct signal and cmp event,
the MG initiates the continuity test tone for the specified
termination. If the return tone is detected before the signal times
out, the cmp event shall be generated with the value of the result
parameter equal to success. In all other cases, the cmp event shall
be generated with the value of the result parameter equal to failure.
When a MGC wants the MG to respond to a continuity test, it sends a
command to the MG containing a signals descriptor with the rsp
signal. Upon reception of a command with the rsp signal, the MG
awaits reception of the continuity test tone. When the tone is
received before the rsp signal times out, the MG returns the
applicable return tone. If the rsp signal times out, the MG removes
the detection and the return tone (if that was playing).
When a continuity test is performed on a termination, no echo devices
or codecs shall be active on that termination.
Performing voice path assurance as part of continuity testing is
provisioned by bilateral agreement between network operators.
Maximum Jitter Buffer
---------------------
PropertyID: jit (0x0007)
This property puts a maximum size on the jitter buffer.
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Type: integer in milliseconds
Possible Values: This property is specified in milliseconds.
Defined In: LocalControlDescriptor
Characteristics: read/write
network failure
---------------
EventID: netfail, 0x0005
The termination generates this event upon detection of a failure due
to external or internal network reasons.
EventDescriptor parameters
None
ObservedEventsDescriptor parameters
cause
-----
ParameterID: cs (0x0001)
Type: String
Possible values: any text string
This parameter may be included with the failure event to provide
diagnostic information on the reason of failure.
quality alert
-------------
EventID: qualert, 0x0006
This property allows the MG to indicate a loss of quality of the
network connection. The MG may do this by measuring packet loss,
interarrival jitter, propogation delay and then indicating this using
a percentage of quality loss.
EventDescriptor parameters
Threshold
---------
ParameterId: th (0x0001)
Cuervo, et al. Standards Track [Page 151]
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Type: integer
Possible Values: threshold for percent of quality loss
measured, calculated based on a provisioned method, that could
take into consideration packet loss, jitter, and delay for
example. Event is triggered when calculation exceeds the
threshold.
ObservedEventsDescriptor parameters
Threshold
---------
ParameterId: th (0x0001)
Type: integer
Possible Values: percent of quality loss measured, calculated
based on a provisioned method, that could take into
consideration packet loss, jitter, and delay for example.
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
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Possible Values: any 64 bit integer
PackageID: rtp (0x000c)
Version: 1
Extends: Network Package version 1
This package is used to support packet based multimedia data transfer
by means of the Real-time Transport Protocol (RTP) [RFC 1889].
Payload Transition EventID: pltrans, 0x0001 This event detects and
notifies when there is a transition of the RTP payload format from
one format to another.
EventDescriptor parameters
None
ObservedEventsDescriptor parameters
rtppayload
----------
ParameterID: rtppltype, 0x01
Type: list of enumerated types.
Possible values: The encoding method shall be specified by
using one or several valid encoding names, as defined in the
RTP AV Profile or registered with IANA.
Packets Sent ------------ StatisticID: ps (0x0004)
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Type: double
Possible Values: any 64 bit integer
Packets Received ---------------- StatisticID: pr (0x0005)
Type: double
Possible Values: any 64 bit integer
Packet Loss ----------- StatisticID: pl (0x0006)
Describes the current rate of packet loss on an RTP stream, as
defined in IETF RFC 1889. Packet loss is expressed as percentage
value: number of packets lost in the interval between two reception
reports, divided by the number of packets expected during that
interval.
Type: double
Possible Values: a 32 bit whole number and a 32 bit fraction.
Jitter
------
StatisticID: jit (0x0007)
Requests the current value of the interarrival jitter on an RTP
stream as defined in IETF RFC 1889. Jitter measures the variation in
interarrival time for RTP data packets.
Delay
-----
StatisticID:delay (0x0008)
Requests the current value of packet propagation delay expressed in
timestamp units. Same as average latency.
PackageID: tdmc (0x000d)
Version: 1
Extends: Network Package version 1
This package is used to support TDM circuit terminations.
Cuervo, et al. Standards Track [Page 154]
RFC 2885 Megaco Protocol August 2000
Echo Cancellation
-----------------
PropertyID: ec (0x0008)
By default, the telephony gateways always perform echo cancellation.
However, it is necessary, for some calls, to turn off these
operations.
Type: boolean
Possible Values:
"on" (when the echo cancellation is requested) and
"off" (when it is turned off.)
The default is "on".
Defined In: LocalControlDescriptor
Characteristics: read/write
Gain Control
------------
PropertyID: gain (0x000a)
Gain control, or usage of of signal level adaptation and noise level
reduction is used to adapt the level of the signal. However, it is
necessary, for example for modem calls, to turn off this function.
Type: enumeration (integer)
Possible Values:
The gain control parameter may either be specified as "automatic"
(0xffffffff), or as an explicit number of decibels of gain (any other
integer value). The default is provisioned in the MG.
Defined In: LocalControlDescriptor
Characteristics: read/write
None
Cuervo, et al. Standards Track [Page 156]
RFC 2885 Megaco Protocol August 2000
APPENDIX A EXAMPLE CALL FLOWS (INFORMATIVE)
All Megaco implementors must read the normative part of this document
carefully before implementing from it. No one should use the examples
in this section as stand-alone explanations of how to create protocol
messages.
The examples in this section use SDP for encoding of the Local and
Remote stream descriptors. SDP is defined in RFC 2327. If there is
any discrepancy between the SDP in the examples, and RFC 2327, the
RFC should be consulted for correctness. Audio profiles used are
those defined in RFC 1890, and others registered with IANA. For
example, G.711 A-law is called PCMA in the SDP, and is assigned
profile 0. G.723 is profile 4, and H263 is profile 34. See also
http://www.iana.org/numbers.htm#R
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.
Behavior
The following illustrates the API invocations from the Media Gateway
Controller and Media Gateways to get the Terminations in this
scenario programmed for idle behavior. Both the originating and
terminating Media Gateways have idle AnalogLine Terminations
programmed to look for call initiation events (i.e.-offhook) by using
the Modify Command with the appropriate parameters. The null Context
is used to indicate that the Terminations are not yet involved in a
Context. The ROOT termination is used to indicate the entire MG
instead of a termination within the MG.
Cuervo, et al. Standards Track [Page 157]
RFC 2885 Megaco Protocol August 2000
In this example, MG1 has the IP address 124.124.124.222, MG2 is
125.125.125.111, and the MGC is 123.123.123.4. The default Megaco
port is 55555 for all three.
1. An MG registers with an MGC using the ServiceChange command:
MG1 to MGC:
MEGACO/1 [124.124.124.222]
Transaction = 9998 {
Context = - {
ServiceChange = ROOT {Services {
Method=Restart,
ServiceChangeAddress=55555, Profile=ResGW/1}
}
}
}
2. The MGC sends a reply:
MGC to MG1:
MEGACO/1 [123.123.123.4]:55555
Reply = 9998 {
Context = - {ServiceChange = ROOT {
Services {ServiceChangeAddress=55555, Profile=ResGW/1} } }
}
3. The MGC programs a Termination in the NULL context. The
terminationId is A4444, the streamId is 1, the requestId in the
Events descriptor is 2222. The mId is the identifier of the sender
of this message, in this case, it is the IP address and port
[123.123.123.4]:55555. Mode for this stream is set to SendReceive.
"al" is the analog line supervision package.
MGC to MG1:
MEGACO/1 [123.123.123.4]:55555
Transaction = 9999 {
Context = - {
Modify = A4444 {
Media { Stream = 1 {
LocalControl {
Mode = SendReceive,
ds0/gain=2, ; in dB,
ds0/ec=G165
},
Local {
v=0
c=IN IP4 $
Cuervo, et al. Standards Track [Page 158]
RFC 2885 Megaco Protocol August 2000
m=audio $ RTP/AVP 0
a=fmtp:PCMU VAD=X-NNVAD ; special voice activity
; detection algorithm
}
}
},
Events = 2222 {al/of}
}
}
}
The dialplan script could have been loaded into the MG previously.
Its function would be to wait for the OffHook, turn on dialtone and
start collecting DTMF digits. However in this example, we use the
digit map, which is put into place after the offhook is detected
(step 5 below).
Note that the embedded EventsDescriptor could have been used to
combine steps 3 and 4 with steps 8 and 9, eliminating steps 6 and 7.
4. The MG1 accepts the Modify with this reply:
MG1 to MGC:
MEGACO/1 [124.124.124.222]:55555
Reply = 9999 {
Context = - {Modify = A4444}
}
5. A similar exchange happens between MG2 and the MGC, resulting in
an idle Termination called A5555.
The following builds upon the previously shown conditions. It
illustrates the transactions from the Media Gateway Controller and
originating Media Gateway (MG1) to get the originating Termination
(A4444) through the stages of digit collection required to initiate a
connection to the terminating Media Gateway (MG2).
6. MG1 detects an offhook event from User 1 and reports it to the
Media Gateway Controller via the Notify Command.
MG1 to MGC:
MEGACO/1 [124.124.124.222]:55555
Transaction = 10000 {
Context = - {
Notify = A4444 {ObservedEvents =2222 {
19990729T22000000:al/of}}
Cuervo, et al. Standards Track [Page 159]
RFC 2885 Megaco Protocol August 2000
}
}
7. And the Notify is acknowledged.
MGC to MG1:
MEGACO/1 [123.123.123.4]:55555
Reply = 10000 {
Context = - {Notify = A4444}
}
8. The MGC Modifies the termination to play dial tone, to look for
digits according to Dialplan0 and to look for the on-hook event now.
MGC to MG1:
MEGACO/1 [123.123.123.4]:55555
Transaction = 10001 {
Context = - {
Modify = A4444 {
Events = 2223 {
al/on, dd/ce {DigitMap=Dialplan0}
},
Signals {cg/dt},
DigitMap= Dialplan0{
(0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)}
}
}
}
9. And the Modify is acknowledged.
MG1 to MGC:
MEGACO/1 [124.124.124.222]:55555
Reply = 10001 {
Context = - {Modify = A4444}
}
10. Next, digits are accumulated by MG1 as they are dialed by User
1. Dialtone is stopped upon detection of the first digit. When an
appropriate match is made of collected digits against the currently
programmed Dialplan for A4444, another Notify is sent to the Media
Gateway Controller.
MG1 to MGC:
MEGACO/1 [124.124.124.222]:55555
Transaction = 10002 {
Context = - {
Notify = A4444 {ObservedEvents =2223 {
Cuervo, et al. Standards Track [Page 160]
RFC 2885 Megaco Protocol August 2000
19990729T22010001:dd/ce{ds="916135551212",Meth=FM}}}
}
}
11. And the Notify is acknowledged.
MGC to MG1:
MEGACO/1 [123.123.123.4]:55555
Reply = 10002 {
Context = - {Notify = A4444}
}
12. The controller then analyses the digits and determines that a
connection needs to be made from MG1 to MG2. Both the TDM
termination A4444, and an RTP termination are added to a new context
in MG1. Mode is ReceiveOnly since Remote descriptor values are not
yet specified. Preferred codecs are in the MGC's preferred order of
choice.
MGC to MG1:
MEGACO/1 [123.123.123.4]:55555
Transaction = 10003 {
Context = $ {
Add = A4444,
Add = $ {
Media {
Stream = 1 {
LocalControl {
Mode = ReceiveOnly,
nt/jit=40, ; in ms
},
Local {
v=0
c=IN IP4 $
m=audio $ RTP/AVP 4
a=ptime:30
v=0
c=IN IP4 $
m=audio $ RTP/AVP 0
}
}
}
}
}
}
Cuervo, et al. Standards Track [Page 161]
RFC 2885 Megaco Protocol August 2000
NOTE - The MGC states its preferred parameter values as a series of
sdp blocks in Local. The MG fills in the Local Descriptor in the
Reply.
13. MG1 acknowledges the new Termination and fills in the Local IP
address and UDP port. It also makes a choice for the codec based on
the MGC preferences in Local. MG1 sets the RTP port to 2222.
MEGACO/1 [124.124.124.222]:55555
Reply = 10003 {
Context = 2000 {
Add = A4444,
Add=A4445{
Media {
Stream = 1 {
Local {
v=0
c=IN IP4 124.124.124.222
m=audio 2222 RTP/AVP 4
a=ptime:30
a=recvonly
} ; RTP profile for G.723 is 4
}
}
}
}
}
14. The MGC will now associate A5555 with a new Context on MG2, and
establish an RTP Stream (i.e, A5556 will be assigned), SendReceive
connection through to the originating user, User 1. The MGC also
sets ring on A5555.
MGC to MG2:
MEGACO/1 [123.123.123.4]:55555
Transaction = 50003 {
Context = $ {
Add = A5555 { Media {
Stream = 1 {
LocalControl {Mode = SendReceive} }},
Events=1234{al/of}
Signals {al/ri}
},
Add = $ {Media {
Stream = 1 {
LocalControl {
Mode = SendReceive,
nt/jit=40 ; in ms
},
Cuervo, et al. Standards Track [Page 162]
RFC 2885 Megaco Protocol August 2000
Local {
v=0
c=IN IP4 $
m=audio $ RTP/AVP 4
a=ptime:30
},
Remote {
v=0
c=IN IP4 124.124.124.222
m=audio 2222 RTP/AVP 4
a=ptime:30
} ; RTP profile for G.723 is 4
}
}
}
}
}
15. This is acknowledged. The stream port number is different from
the control port number. In this case it is 1111 (in the SDP).
MG2 to MGC:
MEGACO/1 [124.124.124.222]:55555
Reply = 50003 {
Context = 5000 {
Add = A5555{}
Add = A5556{
Media {
Stream = 1 {
Local {
v=0
c=IN IP4 125.125.125.111
m=audio 1111 RTP/AVP 4
}
} ; RTP profile for G723 is 4
}
}
}
}
16. The above IPAddr and UDPport need to be given to MG1 now.
MGC to MG1:
MEGACO/1 [123.123.123.4]:55555
Transaction = 10005 {
Context = 2000 {
Modify = A4444 {
Cuervo, et al. Standards Track [Page 163]
RFC 2885 Megaco Protocol August 2000
Signals {cg/rt}
},
Modify = A4445 {
Media {
Stream = 1 {
Remote {
v=0
c=IN IP4 125.125.125.111
m=audio 1111 RTP/AVP 4
}
} ; RTP profile for G723 is 4
}
}
}
}
MG1 to MGC:
MEGACO/1 [124.124.124.222]:55555
Reply = 10005 {
Context = 2000 {Modify = A4444, Modify = A4445}
}
17. The two gateways are now connected and User 1 hears the
RingBack. The MG2 now waits until User2 picks up the receiver and
then the two-way call is established.
From MG2 to MGC:
MEGACO/1 [125.125.125.111]:55555
Transaction = 50005 {
Context = 5000 {
Notify = A5555 {ObservedEvents =1234 {
19990729T22020002:al/of}}
}
}
From MGC to MG2:
MEGACO/1 [123.123.123.4]:55555
Reply = 50005 {
Context = - {Notify = A5555}
}
From MGC to MG2:
MEGACO/1 [123.123.123.4]:55555
Transaction = 50006 {
Cuervo, et al. Standards Track [Page 164]
RFC 2885 Megaco Protocol August 2000
Context = 5000 {
Modify = A5555 {
Events = 1235 {al/on},
Signals { } ; to turn off ringing
}
}
}
From MG2 to MGC:
MEGACO/1 [125.125.125.111]:55555
Reply = 50006 {
Context = 5000 {Modify = A4445}
}
18. Change mode on MG1 to SendReceive, and stop the ringback.
MGC to MG1:
MEGACO/1 [123.123.123.4]:55555
Transaction = 10006 {
Context = 2000 {
Modify = A4445 {
Media {
Stream = 1 {
LocalControl {
Mode=SendReceive
}
}
}
},
Modify = A4444 {
Signals { }
}
}
}
from MG1 to MGC:
MEGACO/1 [124.124.124.222]:55555
Reply = 10006 {
Context = 2000 {Modify = A4445, Modify = A4444}}
19. The MGC decides to Audit the RTP termination on MG2.
MEGACO/1 [123.123.123.4]:55555
Transaction = 50007 {
Context = - {AuditValue = A5556{
Audit{Media, DigitMap, Events, Signals, Packages, Statistics
}}
Cuervo, et al. Standards Track [Page 165]
RFC 2885 Megaco Protocol August 2000
}
}
20. The MG2 replies. An RTP termination has no events nor signals,
so these are left out in the reply .
MEGACO/1 [125.125.125.111]:55555
Reply = 50007 {
Context = - {
AuditValue = A5556 {
Media {
Stream = 1 {
LocalControl { Mode = SendReceive,
nt/jit=40 },
Local {
v=0
c=IN IP4 125.125.125.111
m=audio 1111 RTP/AVP 4
a=ptime:30
},
Remote {
v=0
c=IN IP4 124.124.124.222
m=audio 2222 RTP/AVP 4
a=ptime:30
} } },
Packages {nt-1, rtp-1},
Statistics { rtp/ps=1200, ; packets sent
nt/os=62300, ; octets sent
rtp/pr=700, ; packets received
nt/or=45100, ; octets received
rtp/pl=0.2, ; % packet loss
rtp/jit=20,
rtp/delay=40 } ; avg latency
}
}
}
21. When the MGC receives an onhook signal from one of the MGs, it
brings down the call. In this example, the user at MG2 hangs up
first.
From MG2 to MGC:
MEGACO/1 [125.125.125.111]:55555
Transaction = 50008 {
Context = 5000 {
Notify = A5555 {ObservedEvents =1235 {
Cuervo, et al. Standards Track [Page 166]
RFC 2885 Megaco Protocol August 2000
19990729T24020002:al/on}
}
}
}
From MGC to MG2:
MEGACO/1 [123.123.123.4]:55555
Reply = 50008 {
Context = - {Notify = A5555}
}
22. The MGC now sends both MGs a Subtract to take down the call.
Only the subtracts to MG2 are shown here. Each termination has its
own set of statistics that it gathers. An MGC may not need to
request both to be returned. A5555 is a physical termination, and
A5556 is an RTP termination.
From MGC to MG2:
MEGACO/1 [123.123.123.4]:55555
Transaction = 50009 {
Context = 5000 {
Subtract = A5555 {Audit{Statistics}},
Subtract = A5556 {Audit{Statistics}}
}
}
From MG2 to MGC:
MEGACO/1 [125.125.125.111]:55555
Reply = 50009 {
Context = 5000 {
Subtract = A5555 {
Statistics {
nt/os=45123, ; Octets Sent
nt/dur=40 ; in seconds
}
},
Subtract = A5556 {
Statistics {
rtp/ps=1245, ; packets sent
nt/os=62345, ; octets sent
rtp/pr=780, ; packets received
nt/or=45123, ; octets received
rtp/pl=10, ; % packets lost
rtp/jit=27,
Cuervo, et al. Standards Track [Page 167]
RFC 2885 Megaco Protocol August 2000
rtp/delay=48 ; average latency
}
}
}
}
23. The MGC now sets up both MG1 and MG2 to be ready to detect the
next off-hook event. See step 1. Note that this could be the default
state of a termination in the null context, and if this were the
case, no message need be sent from the MGC to the MG. Once a
termination returns to the null context, it goes back to the default
termination values for that termination.
Authors' Addresses
Fernando Cuervo
Nortel Networks
P.O. Box 3511, Station C
Ottawa, ON K1Y 4H7
Canada
E-mail: fcuervo@nortelnetworks.com
Nancy Greene
Nortel Networks
P.O. Box 3511, Station C
Ottawa, ON K1Y 4H7
Canada
E-mail: ngreene@nortelnetworks.com
Christian Huitema
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
USA
E-mail: huitema@microsoft.com
Abdallah Rayhan
Nortel Networks
P.O. Box 3511, Station C
Ottawa, ON K1Y 4H7
Canada
E-mail: arayhan@nortelnetworks.com
Cuervo, et al. Standards Track [Page 168]
RFC 2885 Megaco Protocol August 2000
Brian Rosen
Marconi
1000 FORE Drive
Warrendale, PA 15086
USA
E-mail: brian.rosen@marconi.com
John Segers
Lucent Technologies, Room HE 303
Dept. Forward Looking Work
P.O. Box 18, 1270 AA Huizen
The Netherlands
E-mail: jsegers@lucent.com
Cuervo, et al. Standards Track [Page 169]
RFC 2885 Megaco Protocol August 2000
Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
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The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Cuervo, et al. Standards Track [Page 170]