28 May, 1996

 

SOURCE :   SG15 Plenary May 28, 1966

 

             

 

             

TITLE  :Draft Recommendation H.323: VISUAL TELEPHONE SYSTEMS AND     EQUIPMENT FOR LOCAL AREA  NETWORKS  WHICH  PROVIDE  A  NON-GUARANTEED  QUALITY  OF  SERVICE

 

This document reflects changes to COM15-245 (H.323) approved by the May 28 Plenary of SG15.  It is the final master for the decided H.323.  It has no change marks.  The file name is p323ncm3.doc.  This document results from the application of the changes in the file h323wtd8.doc to the white document COM15-245 to produce the change marked document h323wht8.doc.  When the changes are accepted the result is p323ncm3.doc.

 

INTERNATIONAL  TELECOMMUNICATION  UNION

 

ITU-T                        H.323

TELECOMMUNICATION                                                                           May 28, 1996
STANDARDIZATION  SECTOR                                                           Decided May 28, 1996
OF  ITU

 

 

LINE  TRANSMISSION  OF  NON-TELEPHONE
SIGNALS

 

VISUAL  TELEPHONE  SYSTEMS  AND   EQUIPMENT FOR  LOCAL  AREA  NETWORKS  WHICH  PROVIDE  A  NON-GUARANTEED  QUALITY  OF  SERVICE

DRAFT  ITU-T  Recommendation  H.323

                       

 

 

 

 

 

FOREWORD

 

The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Tele­com­munication Union.  The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.

The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics.

ITU-T Recommendation H.323 was prepared by the ITU-T Study Group 15 (199x-199x) and was approved by the WTSC (Place, Month xx-xx, 199x).

___________________

 

 

 

 

 

ã  ITU  199x

All rights reserved.  No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.

 

SUMMARY

 

Recommendation H.323 describes terminals, equipment, and services for multimedia communication over Local Area Networks (LAN) which do not provide a guaranteed Quality of Service.  H.323 terminals and equipment may carry real-time voice, data, and video, or any combination, including videotelephony.

The LAN over which H.323 terminals communicate, may be a single segment or ring, or it may be multiple segments with complex topologies.  It should be noted that operation of H.323 terminals over the multiple LAN segments (including the Internet) may result in poor performance.  The possible means by which quality of service might be assured on such types of LANs/internetworks is beyond the scope of this recommendation.

H.323 terminals may be integrated into personal computers or implemented in stand-alone devices such as videotelephones.  Support for voice is mandatory, while data and video are optional, but if supported, the ability to use a specified common mode of operation is required, so that all terminals supporting that media type can interwork.  H.323 allows more than one channel of each type to be in use.  Other Recommendations in the H.323 series include H.225.0 packet and synchronization, H.245 control, H.261 and H.263 video codecs, G.711, G.722, G.728, G.729, and G.723 audio codecs, and the T.120 series of multimedia communications protocols.

H.323 makes use of the logical channel signalling procedures of Recommendation H.245, in which the content of each logical channel is described when the channel is opened.  Procedures are provided for expression of receiver and transmitter capabilities, so transmissions are limited to what receivers can decode, and so that receivers may request a particular desired mode from transmitters.  Since the procedures of H.245 are also used by Recommendation H.310 for ATM networks, Recommendation H.324 for GSTN, and V.70, interworking with these systems should not require H.242 to H.245 translation as would be the case for H.320 systems.

H.323 terminals may be used in multipoint configurations, and may interwork with H.310 terminals on B-ISDN, H.320 terminals on N-ISDN, H.321 terminals on B-ISDN, H.322 terminals on Guaranteed Quality of Service LANs, H.324 terminals on GSTN and wireless networks, and V.70 terminals on GSTN.

Table of Contents

SUMMARY..........................................................................................................................................

1 Scope.............................................................................................................................................

2 Normative references......................................................................................................

3 Definitions..................................................................................................................................

4 Symbols and abbreviations...........................................................................................

5 Conventions.............................................................................................................................

6 System description............................................................................................................

6.1 Information Streams.................................................................................................................................................................

6.2 Terminal Characteristics........................................................................................................................................................

6.2.1 Terminal elements outside the scope of H.323................................................................................................................

6.2.2 Terminal elements within the scope of H.323..................................................................................................................

6.2.3 LAN Interface.......................................................................................................................................................................

6.2.4 Video Codec..........................................................................................................................................................................

6.2.4.1 Terminal Based Continuous Presence.......................................................................................................................

6.2.5 Audio Codec.........................................................................................................................................................................

6.2.5.1 Audio Mixing................................................................................................................................................................

6.2.5.2 Maximum Audio-Video Transmit Skew.....................................................................................................................

6.2.6 Receive Path Delay..............................................................................................................................................................

6.2.7 Data Channel........................................................................................................................................................................

6.2.7.1 T.120 Data Channels....................................................................................................................................................

6.2.8 H.245 Control Function.......................................................................................................................................................

6.2.8.1 Capabilities exchange...................................................................................................................................................

6.2.8.2 Logical channel signalling...........................................................................................................................................

6.2.8.3 Mode preferences.........................................................................................................................................................

6.2.8.4 Master Slave Determination........................................................................................................................................

6.2.8.5 Timer and counter values............................................................................................................................................

6.2.9 RAS Signalling Function....................................................................................................................................................

6.2.10 Call Signalling Function....................................................................................................................................................

6.2.11 H.225.0 Layer......................................................................................................................................................................

6.2.11.1 Logical channel numbers...........................................................................................................................................

6.2.11.2 Logical Channel Bitrate Limits..................................................................................................................................

6.3 Gateway Characteristics..........................................................................................................................................................

6.4 Gatekeeper Characteristics....................................................................................................................................................

6.5 Multipoint Controller Characteristics..................................................................................................................................

6.6 Multipoint Processor Characteristics..................................................................................................................................

6.7 Multipoint Control Unit Characteristics..............................................................................................................................

6.8 Multipoint Capability................................................................................................................................................................

6.8.1 Centralized Multipoint Capability......................................................................................................................................

6.8.2 Decentralized Multipoint Capability.................................................................................................................................

6.8.3 Hybrid Multipoint - Centralized Audio.............................................................................................................................

6.8.4 Hybrid Multipoint - Centralized Video..............................................................................................................................

6.8.5 Establishment of Common Mode......................................................................................................................................

6.8.6 Multipoint rate matching....................................................................................................................................................

6.8.7 Multipoint Lip Synchronization.........................................................................................................................................

6.8.8 Multipoint Encryption.........................................................................................................................................................

6.8.9 Cascading Multipoint Control Units.................................................................................................................................

7 Call Signalling.....................................................................................................................

7.1 Addresses....................................................................................................................................................................................

7.1.1 LAN Address.......................................................................................................................................................................

7.1.2 TSAP Identifier.....................................................................................................................................................................

7.1.3 Alias Address.......................................................................................................................................................................

7.2 Registration, Admissions, and Status (RAS) Channel.......................................................................................................

7.2.1 Gatekeeper Discovery.........................................................................................................................................................

7.2.2 Endpoint Registration.........................................................................................................................................................

7.2.3 Endpoint Location...............................................................................................................................................................

7.2.4 Admissions, Bandwidth Change, Status, Disengage.....................................................................................................

7.3 Call Signalling Channel..........................................................................................................................................................

7.3.1 Call Signalling Channel Routing........................................................................................................................................

7.3.2 Control Channel Routing....................................................................................................................................................

7.4 Call Reference Value................................................................................................................................................................

7.5 Conference ID and Conference Goal......................................................................................................................................

8.  Call Signalling Procedures...................................................................................

8.1 Phase A  - Call set-up.............................................................................................................................................................

8.1.1 Basic Call Setup - Neither Endpoint Registered..............................................................................................................

8.1.2 Both Endpoints Registered to the Same Gatekeeper......................................................................................................

8.1.3 Only Calling Endpoint has Gatekeeper.............................................................................................................................

8.1.4 Only Called Endpoint has Gatekeeper..............................................................................................................................

8.1.5 Both Endpoints Registered to Different Gatekeepers....................................................................................................

8.1.6 Call Set-up via Gateways....................................................................................................................................................

8.1.6.1 Gateway Inbound Call Set-up.....................................................................................................................................

8.1.6.2 Gateway Outbound Call Set-up..................................................................................................................................

8.1.7 Call Setup with an MCU......................................................................................................................................................

8.1.8 Call Forwarding....................................................................................................................................................................

8.1.9 Broadcast Call Setup...........................................................................................................................................................

8.2 Phase B - Initial communication and capability exchange.................................................................................................

8.3 Phase C - Establishment of audiovisual communication....................................................................................................

8.3.1 Mode changes......................................................................................................................................................................

8.3.2 Exchange of video by mutual agreement..........................................................................................................................

8.3.3 Media Stream Address Distribution...................................................................................................................................

8.4 Phase D: Call Services.............................................................................................................................................................

8.4.1 Bandwidth Changes............................................................................................................................................................

8.4.2 Status.....................................................................................................................................................................................

8.4.3 Ad Hoc Conference Expansion..........................................................................................................................................

8.4.3.1 Direct Endpoint Call Signalling -  Conference Create............................................................................................

8.4.3.2 Direct Endpoint Call Signalling -  Conference Invite.............................................................................................

8.4.3.3Direct Endpoint Call Signalling -  Conference Join.................................................................................................

8.4.3.4 Gatekeeper Routed Call Signalling - Conference Create.........................................................................................

8.4.3.5 Gatekeeper Routed Call Signaling - Conference Invite...........................................................................................

8.4.3.6 Gatekeeper Routed Call Model - Conference Join...................................................................................................

8.4.4 Supplementary Services......................................................................................................................................................

8.5 Phase E: Call termination........................................................................................................................................................

8.5.1 Call Clearing without a Gatekeeper....................................................................................................................................

8.5.2 Call Clearing with a Gatekeeper..........................................................................................................................................

8.5.3 Call Clearing by Gatekeeper................................................................................................................................................

8.6 Protocol Failure Handling.......................................................................................................................................................

9 Interoperation with other terminal types......................................................

9.1 Speech only terminals..............................................................................................................................................................

9.2 Visual telephone terminals over the ISDN (H.320).............................................................................................................

9.3 Visual telephone terminals over GSTN (H.324)..................................................................................................................

9.4 Visual telephone terminals over Mobile Radio (H.324/M).................................................................................................

9.5 Visual telephone terminals over ATM (H.321)....................................................................................................................

9.6 Visual telephone terminals over Guaranteed Quality of Service LANs (H.322)...........................................................

9.7 Simultaneous Voice and Data Terminals over GSTN (V.70)............................................................................................

9.8 T.120 Terminals on the LAN..................................................................................................................................................

10 Optional enhancements...............................................................................................

10.1 Encryption.................................................................................................................................................................................

11 Maintenance.........................................................................................................................

11.1 Loopbacks for maintenance purposes.................................................................................................................................

11.2  Monitoring Methods............................................................................................................................................................