ETSI EG 202 090 V1.1.2 (1999-03)

SLOVENSKI STANDARD
01-januar-2005
Širokopasovno digitalno omrežje z integriranimi storitvami (B-ISDN) –
Medobratovalnost signalizacij H.323/B-ISDN
Broadband Integrated Services Digital Network (B-ISDN); H.323/B-ISDN signalling
interoperability
Ta slovenski standard je istoveten z: EG 202 090 Version 1.1.2
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EG 202 090 V1.1.2 (1999-03)
ETSI Guide
Broadband Integrated Services Digital Network (B-ISDN);
H.323/B-ISDN signalling interoperability

2 EG 202 090 V1.1.2 (1999-03)
Reference
DEG/SPS-05173 (jco00ide.PDF)
Keywords
ATM, audio, B-ISDN, broadband, interoperability,
IP, ISDN, multimedia, speech, video
ETSI
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ETSI
3 EG 202 090 V1.1.2 (1999-03)
Contents
Intellectual Property Rights . 6
Foreword. 6
1 Scope. 7
2 References . 7
3 Abbreviations. 9
4 Introduction. 10
4.1 Overview of H.323 and related recommendations. 10
4.1.1 H.323 concept and entities . 10
4.1.2 Channels defined in H.323 . 11
4.1.3 Protocols and related standards. 11
4.1.4 Call procedures . 12
4.1.5 Fast connect. 13
4.1.6 Inter-domain signalling . 13
4.2 Overview of modelling work relating to B-ISDN signalling . 13
4.3 Overview of B-ISDN signalling - combined call/bearer control. 15
4.4 Overview of B-ISDN signalling - separated call and bearer control. 15
5 Related work. 16
5.1 ECMA TC32-TG15 and ETSI SPS5 WG5. 16
5.2 ITU-T Study Group 16 . 17
5.3 ETSI project TIPHON. 17
5.3.1 General. 17
5.3.2 Gateway functional decomposition . 19
5.4 ATM Forum SAA/RMOA . 20
5.5 ECMA TC32-TG13. 20
5.6 IETF. 20
5.6.1 SIP. 20
5.6.2 IPTEL. 20
5.6.3 E.164 Birds of a Feather activity. 20
5.6.4 NAVDEC. 20
6 H.323 and modelling of B-ISDN signalling . 20
7 H.323 interworking via a gateway with B-ISDN separated call and bearer control . 21
7.1 Scenarios. 21
7.2 Protocol interworking architecture. 23
7.2.1 Scenario 1. 23
7.2.1.1 Sub-scenario 1a - null session/resource control in B-ISDN - LAN-based H.323 environment . 23
7.2.1.2 Sub-scenario 1b - null session/resource control in B-ISDN - IP-over-ATM-based H.323
environment without H.323 annex C . 24
7.2.1.3 Sub-scenario 1c - null session/resource control in B-ISDN - use of H.323 annex C in H.323
environment. 25
7.2.2 Scenario 2. 25
7.2.2.1 Sub-scenario 2a - each environment operates own session/resource control protocols - LAN-
based H.323 environment . 25
7.2.2.2 Sub-scenario 2b - each environment operates own session/resource control protocols - IP-over-
ATM-based H.323 environment without H.323 annex C . 26
7.2.2.3 Sub-scenario 2c - each environment operates own session/resource control protocols - use of
H.323 annex C in H.323 environment . 27
7.2.3 Scenario 3. 27
7.2.3.1 Sub-scenario 3c - end-to-end session/resource control protocols - use of H.323 annex C in H.323
environment. 27
7.3 Session control in B-ISDN environment. 28
7.4 Resource control in B-ISDN environment. 28
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4 EG 202 090 V1.1.2 (1999-03)
7.5 Call establishment. 29
7.6 Bearer establishment. 29
7.7 Addressing . 30
7.7.1 Addressing in H.323. 30
7.7.2 Addressing in B-ISDN and B-PISN. 31
7.7.3 Address interworking between H.323 and B-ISDN . 31
7.8 Message sequences for basic communication establishment . 32
7.8.1 Scenarios 1a and 1b. 32
7.8.2 Scenario 1c. 34
7.8.3 Scenarios 2a and 2b. 35
7.8.4 Scenario 2c. 37
7.8.5 Scenario 3c. 39
7.9 Generic Functional Protocol . 40
7.10 Supplementary services. 40
7.10.1 Introduction. 40
7.10.2 Supplementary services in scenario 1. 41
7.10.3 Supplementary services in scenario 2. 41
7.10.4 Supplementary services in scenario 3. 41
7.10.5 Areas for further work. 42
7.11 Conferencing. 42
7.12 Impact of T.120 . 42
8 H.323 interworking via a gateway with B-ISDN combined call/bearer control . 42
8.1 Scenarios. 43
8.2 Protocol interworking architecture. 45
8.2.1 Scenario 1. 45
8.2.1.1 Sub-scenario 1a - null session/resource control in B-ISDN - LAN-based H.323 environment . 45
8.2.1.2 Sub-scenario 1b - null session/resource control in B-ISDN - IP-over-ATM-based H.323
environment without H.323 annex C . 45
8.2.1.3 Sub-scenario 1c - null session/resource control in B-ISDN - use of H.323 annex C in H.323
environment. 45
8.2.2 Scenario 2. 45
8.2.2.1 Sub-scenario 2a - each environment operates own session/resource control protocols - LAN-
based H.323 environment . 46
8.2.2.2 Sub-scenario 2b - each environment operates own session/resource control protocols - IP-over-
ATM-based H.323 environment without H.323 annex C . 46
8.2.2.3 Sub-scenario 2c - each environment operates own session/resource control protocols - use of
H.323 annex C in H.323 environment . 46
8.2.3 Scenario 3. 46
8.2.3.1 Sub-scenario 3c - end-to-end session/resource control protocols - use of H.323 annex C in H.323
environment. 46
8.3 Session control in B-ISDN environment. 47
8.4 Resource control in B-ISDN environment. 47
8.5 Call/bearer establishment. 47
8.6 Addressing . 47
8.7 Message sequences for basic communication establishment . 48
8.7.1 Scenarios 1a and 1b. 48
8.7.2 Scenario 1c. 49
8.7.3 Scenarios 2a and 2b. 50
8.7.4 Scenario 2c. 52
8.7.5 Scenario 3c. 53
8.8 Generic functional protocol . 53
8.9 Supplementary services. 54
8.10 Conferencing. 54
8.11 Impact of T.120 . 54
9 Summary of interworking scenarios in 7 and 8 . 54
9.1 Scenario 1 . 54
9.2 Scenario 2 . 54
9.3 Scenario 3 . 55
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5 EG 202 090 V1.1.2 (1999-03)
10 Application of B-ISDN separated protocols to gatekeeper-to-gatekeeper communication. 55
11 Connection of remote H.323 environments via B-ISDN. 55
11.1 Case 1 - full interworking . 56
11.2 Case 2 - tunnelling . 56
11.2.1 Scenario T1 - tunnelling of session and resource control protocols . 56
11.2.1.1 Scenario T1.1 - tunnelling of session and resource control protocols through B-ISDN. 56
11.2.1.2 Scenario T1.2 - transmission of session and resource control protocols through IP network, by-
passing B-ISDN. 57
11.2.2 Scenario T2 - tunnelling of session control protocol only. 57
11.2.3 Scenario T3 - tunnelling of resource control protocol only. 57
11.2.3.1 Scenario T3.1 - tunnelling of resource control protocol through B-ISDN. 57
11.2.3.2 Scenario T3.2 - transmission of resource control protocol through IP network, by-passing
B-ISDN. 58
11.2.4 Additional considerations when endstations employ H.323 annex C (native IP network or IP over
ATM network) . 58
11.2.5 Conclusions on tunnelling scenarios . 58
12 Co-existence of H.323 annex C and B-ISDN signalling in the same network. 59
13 Impact of H.323 on future mobility protocols. 59
13.1 Introduction . 59
13.2 Mobility concepts . 59
13.3 Mobility architecture. 60
13.4 Virtual Home Environment (VHE). 61
14 Conclusions and recommendations . 62
Bibliography . 64
History. 65
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6 EG 202 090 V1.1.2 (1999-03)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect
of ETSI standards", which is available free of charge from the ETSI Secretariat. Latest updates are available on the
ETSI Web server (http://www.etsi.org/ipr).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in SR 000 314 (or the updates on the ETSI Web server)
which are, or may be, or may become, essential to the present document.
Foreword
This ETSI Guide (EG) has been produced by ETSI Technical Committee Signalling Protocols and Switching (SPS).
ETSI
7 EG 202 090 V1.1.2 (1999-03)
1 Scope
The present document is to investigate the interoperability of H.323 and B-ISDN signalling environments with a view to
identifying possible standardization activities in this area. The following aspects of interoperability are investigated:
• the interworking of H.323 and B-ISDN environments, both separated and combined, via a gateway;
• the connection of remote H.323 environments via B-ISDN;
• the use of H.323 annex C (H.323 on ATM), including the co-existence of H.323 annex C and B-ISDN signalling
in the same network and possible future enhancement of annex C;
• the application of the B-ISDN separated call control protocol to gatekeeper-to-gatekeeper communication;
• the impact of H.323 on future mobility protocols.
For each of the above, due consideration is given to the following: addressing impact (including use of IP addressing);
conferencing models; T.120 data impact; basic call procedures; generic functional procedures (GFP) and supplementary
services; end-to-end resource and session level protocols.
Possible future standardization activities resulting from the present document will include H.323 work items as well as
B-ISDN signalling work items.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
• References are either specific (identified by date of publication, edition number, version number, etc.) or non-
specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, subsequent revisions do apply.
• A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same
number.
[1] ECMA-155 (1997): "Private Integrated Services Networks - Addressing".
[2] ECMA-254 (1996): "B-PISN - Inter-Exchange Signalling Protocol - Generic Functional Protocol
(B-QSIG-GF)".
[3] ATM Forum P-NNI V1.0 (1996): "Private Network-Network Interface Specification Version 1.0
(af-pnni-0055.000)".
[4] ATM Forum UNI 4.0 (1996): "ATM User-Network Interface (UNI) Signalling Specification
Version 4.0 (af-sig-0061.000)".
[5] Void.
[6] TR 101 300 (V1.1): "Telecommunications and Internet Protocol Harmonization Over Network
(TIPHON); Description of technical issues".
[7] TS 101 313: "Telecommunications and Internet Protocol Harmonization Over Networks
(TIPHON); Network architecture and reference configurations; Scenario 2".
[8] TS 101 324 (V1.1): "Telecommunications and Internet Protocol Harmonization Over Networks
(TIPHON); Naming and addressing; Scenario 1".
[9] IETF RFC 1483 (1993): "Multiprotocol Encapsulation over ATM Adaptation Layer 5".
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8 EG 202 090 V1.1.2 (1999-03)
[10] IETF RFC 1577 (1994): "Classical IP and ARP over ATM".
[11] ISO/IEC 13247 (1997): "Information technology - Telecommunications and information exchange
between systems - Broadband Private Integrated Services Network - Inter-exchange signalling
protocol - Basic call/connection control".
[12] ISO/IEC 11571: "Information technology - Telecommunications and information exchange
between systems - Numbering and sub-addressing in private integrated services networks".
[13] ITU-T Recommendation H.225.0 (1998): "Call signalling protocols and media stream
packetization for packet based multimedia communication systems".
[14] ITU-T Recommendation H.245 (1998): "Control protocol for multimedia communication".
[15] ITU-T Recommendation H.323 (1998): "Packet based multimedia communication systems".
[16] ITU-T Recommendation H.450.1 (1998): "Generic functional protocol for the support of
supplementary services in H.323".
[17] ITU-T Recommendation H.450.2 (1998): "Call transfer supplementary service for H.323".
[18] ITU-T Recommendation H.450.3 (1998): "Call diversion supplementary service for H.323".
[19] ITU-T Recommendation Q.2726.1 (1996): "B-ISDN user part - ATM end system address".
[20] ITU-T Recommendation Q.2931 (1995): "Digital Subscriber Signalling system No. 2 (DSS 2) -
User-Network Interface (UNI) Layer 3 specification for basic call/connection control".
[21] ITU-T Recommendation Q.2932.1 (1996): "Digital subscriber signalling system No. 2 - Generic
functional protocol: Core functions".
[22] ITU-T Recommendation Q.931 (1993): "ISDN user-network interface layer 3 specification for
basic call control".
[23] ITU-T Recommendation T.120 (1996): "Data protocols for multimedia conferencing".
[24] Void.
[25] Void.
[26] Void.
[27] ITU-T Recommendation H.235: "Security and encryption for H-Series (H.323 and other
H.245-based) multimedia terminals".
[28] ITU-T Recommendation G.711: "Pulse code modulation (PCM) of voice frequencies".
[29] ITU-T Recommendation G.723.1: "Dual rate speech coder for multimedia communications
transmitting at 5.3 and 6.3 kbit/s".
[30] ITU-T Recommendation G.728: "Coding of speech at 16 kbit/s using low-delay code excited linear
prediction".
[31] ITU-T Recommendation G.729: "Coding of speech at 8 kbit/s using conjugate-structure
algebraic-code-excited linear-prediction".
[32] ITU-T Recommendation H.261: "Video codec for audiovisual services at p x 64 kbit/s".
[33] ITU-T Recommendation H.263: "Video coding for low bit rate communication".
[34] ITU-T Recommendation E.164: "The international public telecommunication numbering plan".
[35] ITU-T Recommendation Q. 2761: "Functional description of the B-ISDN user part (B-ISUP) of
signalling system No. 7".
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9 EG 202 090 V1.1.2 (1999-03)
[36] ITU-T Recommendation Q. 2762: "General Functions of messages and signals of the B-ISDN user
part (B-ISUP) of Signalling System No. 7".
[37] ITU-T Recommendation Q. 2763: "Signalling System No. 7 B-ISDN User Part (B-ISUP) -
Formats and codes".
[38] ITU-T Recommendation Q. 2764: "Signalling System No. 7 B-ISDN User Part (B-ISUP) - Basic
call procedures".
[39] ITU-T Recommendation H.246: "Interworking of H-Series multimedia terminals with H-Series
multimedia terminals and voice/voiceband terminals on GSTN and ISDN".
[40] ATM Forum UNI 3.1: "ATM User-Network Interface Specification V3.1".
[41] ITU-T Recommendation E.191: "B-ISDN numbering and addressing".
3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AESA ATM End System Address
AFI Authority and Format Identifier
ATM Asynchronous Transfer Mode
BC Bearer Control
B-HLI Broadband6 High Layer Information
B-ISDN Broadband-ISDN
B-ISUP Broadband-ISDN User Part
B-PISN Broadband-PISN
CC Call Control
CN Core Network
DCC Designated Country Code
GFP Generic Functional Protocol
GFT Generic Functional Transport
GSM Global System Mobile
GSTN General Switched Telephony Network
ICD International Code Designator
IETF International Engineering Task Force
IMT International Mobile Telecommunications
IN Intelligent Network
IP Internet Protocol
ISDN Integrated Services Digital Network
LAN Local Area Network
LANE LAN Emulation
MC Multipoint Controller
MCU Multipoint Control Unit
MGCP Media Gateway Control Protocol
MIB Management Information Base
MP Multipoint Processor
MPLS Multi-Protocol Label Switching
MPOA Multi-Protocol Over ATM
MT Mobile Terminal
NAVDEC Network Access Server and Voice on IP Device Control
NSAP Network Service Access Point
PISN Private Integrated Services Network
PNNI Private Network-to-Network Interface
PNP Private Numbering Plan
PUM Personal User Mobility
PVC Permanent Virtual Circuit
QoS Quality of Service
RAN Radio Access Network
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10 EG 202 090 V1.1.2 (1999-03)
RAS Registration, Admission and Status
RMOA Real-time Multimedia Over ATM
RTCP Real-Time Control Protocol
RTP Real-Time Protocol
SCN Switched Circuit Network
SDP Session Description Protocol
SIP Session-Initiated Protocol
SNMP Simple Network Management Protocol
SS7 Signalling System N°7
SVC Switched Virtual Circuit
TCP Transmission Control Protocol
TE Terminal Equipment
TIPHON Telecommunications and Internet Protocol Harmonization Over Networks
UDP User Datagram Protocol
UIM User Identity Module
UNI User-to-Network Interface
UPT Universal Personal Telephony
URL Universal Resource Locator
VHE Virtual Home Environment
4 Introduction
4.1 Overview of H.323 and related recommendations
4.1.1 H.323 concept and entities
H.323 specifies multimedia conferencing over packet networks. This sentence already contains the keywords for noting
major characteristics of H.323:
• Multimedia: The media mix in a call can consist of audio, video and data streams. Audio communication has to
be supported, video and data are optional. Media can be added, dropped or replaced dynamically during a call.
NOTE 1: A telefax service is being drafted for the next version of H.323.
• Conference: Even a two-party call is considered a special case of a multiparty conference. With regard to audio
or video, multipoint conferencing can be centralized (media processing is done by a central multipoint processor,
MP), decentralized (media are multicast directly from the sending party to all receiving parties), or mixed
(combination of the two). Hybrid conferences combining centralized audio with decentralized video, or vice
versa, are possible. Control information is always centralized via a Multipoint Controller (MC). Data traffic is
also distributed centrally.
• Packet network: Although H.323 is independent of the specific transport substructure, its main sphere seems to
be TCP/IP based networks (LANs/intranets or internet). The network provides a transparent transport service
between communicating entities, i.e. the entities communicate end-to-end without any "exchange" or "switch"
between them.
H.323 entities are terminals, gateways, gatekeepers, MCs, MPs and multipoint control units (MCUs). An MCU consists
of an MC and optionally one or more MPs.
Terminals, gateways and MCUs are endpoints, which can place and accept calls (i.e. they are "callable").
A gatekeeper is not an endpoint and is "addressable" but not callable. It performs for endpoints in its "zone" tasks such
as address resolution, admission control and bandwidth control.
MCs and MPs are neither addressable nor callable, but are part of an endpoint or gatekeeper which is
addressable/callable.
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11 EG 202 090 V1.1.2 (1999-03)
H.323 uses the terms call and conference in the following way:
- A call is the point-to-point multimedia communication between two H.323 endpoints, either direct or via
gatekeeper(s) and/or MC(s). In case of interworking, the H.323 call consists of the section between the gateway
and another H.323 endpoint.
- A point-to-point conference is the multimedia communication between two terminals irrespective of their
location. In case of interworking, it contains a section between the gateway and another H.323 endpoint, and also
a section in the other network.
- A multiparty conference is the multimedia communication between three or more terminals irrespective of their
location, but including at least one MC. A point-to-point conference becomes a multiparty conference by adding
parties, and vice versa by dropping parties.
NOTE 2: The term 'conference' in H.323 corresponds to the term 'session' in the B-ISDN information model.
4.1.2 Channels defined in H.323
H.323 uses the concept of channels to structure the information exchange between communicating entities. The
following channels are part of the communication process:
• Call signalling channel. This reliable channel carries information for call control and supplementary service
control. The Q.931-like protocol used over this channel is specified in H.225.0 and in H.450.x (for
supplementary services).
• H.245 control channel. This reliable channel carries the H.245 protocol for media control.
• RAS channel. This unreliable channel provides for communication between an endpoint and its gatekeeper. The
RAS (Registration, Admission and Status) protocol is specified in H.225.0.
• Logical channels for media. Usually each real-time medium is carried in a separate pair of uni-directional
unreliable channels, one for each direction, using the RTP and RTCP protocols. A call with audio and video
therefore involves at least four logical channels. Data traffic, however, uses a bi-directional reliable channel and a
protocol stack according to T.120.
In this list, a 'reliable channel' means connection-mode transport, while 'unreliable' refers to connectionless transport. In
an IP-based scenario, this corresponds to TCP and UDP, respectively.
Annex C of H.323 provides a means of carrying real-time media information (audio or video) over an ATM SVC
instead of over UDP/IP when an ATM path exists endstation-to-endstation. This allows the real-time media to take
advantage of the QoS guarantees that ATM provides. Other H.323-related protocols are still carried over TCP/IP or
UDP/IP, using an IP/ATM (e.g. MPLS, MPOA, LANE, RFC 1577, RFC 1483) technique. If audio or video is carried
over ATM according to annex C of H.323, a bi-directional logical channel may be used instead of a pair of
uni-directional channels, thereby resulting in a single SVC used bi-directionally instead of two SVCs used
uni-directionally.
4.1.3 Protocols and related standards
H.323 itself does not specify protocols but normatively refers to a number of other ITU-T Recommendations H.225.0,
H.245, H.235, H.450.x, T.120 etc.
H.225.0 covers three areas:
• Call signalling. A protocol loosely based on Q.931 is specified for call establishment. Its main purpose is to
obtain a transport address for an H.245 connection. Except in the fast connect case (see 4.1.5), where no H.245
connection exists, a call is not cleared when a call signalling connection terminates. Call clearing is normally
done by H.245 signalling. However, for the sake of supplementary service usage, the H.225.0 call signalling
connection may be kept until call release.
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12 EG 202 090 V1.1.2 (1999-03)
• RAS protocol. This protocol between endpoint and gatekeeper provides the following major functions:
- Gatekeeper discovery. Enables an endpoint to find its responsible gatekeeper.
- Endpoint Registration/Unregistration. A terminal or gateway registers with a gatekeeper to enable
participation in calls. An endpoint may unregister if it is not to take part in further calls.
- Admission. Enables a terminal or gateway to get permission to set up or accept a call.
- Bandwidth changes. Instructs or permits an endpoint to change the bandwidth for an existing call.
- Endpoint Location. Locates endpoints based on their alias addresses and returns a transport address (IP
address + port number) where they can be called.
- Disengage. Informs the gatekeeper of call release or instructs the endpoint to terminate a call.
- Status. Keeps the gatekeeper informed of the status of a call.
• RTP/RTCP. H.225.0 specifies the use of the RTP and RTCP protocols for audio and video streams in an H.323
call.
H.245 operates between two endpoints or between an endpoint and an MCU and provides the following functionality:
• capabilities exchange;
• opening and closing of logical channels;
• mode requests;
• master-slave determination;
• flow control;
• call clearing;
• media loop.
Also there are various other H.245 messages that are indicated as applicable in annex A of H.323 but for which there are
no H.323-specific detailed procedures. These include round trip delay determination (can be used as a heartbeat
mechanism) and various conference commands, requests and indications.
H.235 deals with security issues for H.323 calls.
H.450.x series of recommendations specifies generic procedures (H.450.1) and specific protocols for supplementary
services (currently call transfer and call diversion; several others in the drafting state).
T.120 is used as data conferencing protocol. A T.120 conference is treated as a logical channel with its own protocol
suite.
Another important aspect is the coding of user plane information. A number of recommendations apply here, including
G.711, G.723.1, G.728, and G.729 for audio coding and H.261 and H.263 for video coding.
4.1.4 Call procedures
This subclause summarizes the steps involved in a simple H.323 call where gatekeepers are in use. A terminal may
participate in a call if it has registered with its associated gatekeeper. The actual procedures may be more complex than
described here since there are various options for routeing the call control and H.245 control channels either directly
between endpoints or via one or more gatekeepers. Also the adding or dropping of other parties is not considered here.
The calling terminal wishing to place a call may either know the transport address (IP address) or have an alias address
of the destination (e.g. an E.164 number). In the latter case the terminal may ask the gatekeeper(s) for endpoint location,
passing the alias address to the gatekeeper(s), which will return a transport address. This explicit location procedure
allows multicasting of the request to many gatekeepers. Usually, however, the address resolution is implicit in the
admission procedure between an endpoint and its associated gatekeeper, as described below.
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13 EG 202 090 V1.1.2 (1999-03)
The first step of call establishment is taken by the terminal by asking the gatekeeper for call admission, passing the
destination (alias and/or transport) address to the gatekeeper. If granted admission, the terminal will send a SETUP
message to the transport address returned by the gatekeeper. At the destination side, the called endpoint asks its
gatekeeper for admission to accept the incoming call. If granted, the call will be accepted, and a transport address for the
H.245 control channel is returned to the calling endpoint. The H.245 control channel is then established, and the further
call related signalling is done via H.245: exchange of capabilities between calling and called endpoint, master-slave
determination, opening and closing of logical channels etc. Once a logical channel is open, user data can be sent on it.
During the lifetime of a call an endpoint and its associated gatekeeper may exchange status messages or bandwidth
change messages. A call is cleared by closing all logical channels, sending a command to end the session (call) on the
H.245 control channel and releasing the H.245 control channel. The call control channel can be released at any time
after the H.245 control channel is established, at the latest at call clearing.
4.1.5 Fast connect
Fast connect is an option specified in 8.1.7 of H.323 that reduces the number of round trip delays involved in
establishing a call and initial media streams by including H.245 open logical channel information in the SETUP and
CONNECT messages. A separate H.245 channel using its own TCP connection may or may not subsequently be
established, depending on the need for further channel opening and closing during the call. Fast connect is also
mandated in the new H.323 annex F ("Single Use Device"), currently determined in Study Group 16.
Related to this is the use of UDP instead of TCP for signalling, as specified in new H.323 annex E. Both annex E and
annex F will appear in H.323 version 3 shortly.
4.1.6 Inter-domain signalling
A new annex G to H.225.0, currently in a "determined" state in SG16, covers inter-domain address resolution aspects.
The protocol operates between administrative domain border gatekeepers and between border gatekeepers and clearing
houses. It allows an administrative domain to obtain routing addresses for calls to destinations in other domains.
4.2 Overview of modelling work relating to B-ISDN signalling
Work under Question 6 in ITU-T Study Group 11 has developed in document TRQ.2001an information model for
future B-ISDN signalling capabilities. The information model comprises a number of object classes and associations.
Object classes are grouped into four service levels as follows:
• session service level;
• resource service level;
• call service level;
• bearer service level.
The majority of the object classes involved are shown in figure x/TRQ.2001 reproduced in Figure 1.
ETSI
14 EG 202 090 V1.1.2 (1999-03)
Session Service
Level
Session
0.*
Remote Session Local Session
1.*
0.*
Party End Point Party End Point
Remote Session
Direct Session
Association
Association
0.* 0.*
0.*
Resource Service
Level Resource Group
0.* 0.*
0.*
Remote RG Local RG
1.*
0.*
Party End Point Party End Point
Remote RG Direct RG
Association
Association
0.*
0.*
1.*
Resource
1.* 1.*
1.*
0.*
Remote Resource Local Resource
Remote Resource Local Resource
1.*
0.*
Party End Point Party End Point
Component Component
Remote Resource Direct Resource
0.1 0.* 0.* 0.1
Association
Association
0.* 0.*
Call Service
Level
Network View
Remote
1.*
Local
Call
Service Component
Service Component
1.* 1.*
0.*
Remote Call Local Call
0.*
0.*
Party End Point Party End Point
Remote Call Direct Call
Association
Association
0.* 0.*
Bearer Service
Level
Remote NC
Direct NC
0.*
0.*
Association Association
0.* 0.*
Remote NC Local NC
0.*
0.*
Party End Point Party End Point
0.*
0.*
Remote
Remote Bearer
Network Loca
...