1、STD-ITU-T RECMN H-332-ENGL 1776 48b259L Ob53b29 O20 11111 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU H.332 (09i98) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS Infrastructure of audiovisual services - Systems and terminal equipment for audiovisual ser
2、vices H.323 extended for loosely coupled conferences ITU-T Recommendation H.332 (Previously CCITT Recommendation) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS Characte
3、ristics of transmission channels used for other than telephone purposes Use of telephone-type circuits for voice-frequency telegraphy Telephone circuits or cables used for various types of telegraph transmission or simultaneous transmission Telephone-type circuits used for facsimile telegraphy Chara
4、cteristics of data signals CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS INFRASTRUCTURE OF AUDIOVISUAL SERVI CES General Transmission multiplexing and synchronization Systems aspects Communication procedures Coding of moving video Related systems aspects H. I O-H. 1 9 H .20-H .29 H.30-H.39 H.40-H.49 H
5、.50-H.99 H. I OO-H. 199 H.200-H.219 H.220-H.229 H.230-H.239 H.240-H.259 H.260-H.279 H.280-H.299 11 Systems and terminal equipment for audiovisual services H.300-H.399 Supplementary services for multimedia H.450-H.499 II For further details, please refer to ITU-T List of Reconzmendations. COPYRIGHT I
6、nternational Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesITU-T RECOMMENDATION H.332 H.323 EXTENDED FOR LOOSELY COUPLED CONFERENCES Summary This Recommendation describes terminals, equipment, and services for multimedia communication over packet-based netwo
7、rks. H.332 terminals and equipment may carry real-time voice, data, and video in any combination. The goal is to work within the framework of Recommendation H.323, yet provide scalability well beyond the limits of Recommendation H.323 to enable applications involving hundreds and thousands of partic
8、ipants. H.3 32 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 term
9、inals supporting that media type can interwork. Like Recommendation H.323, this Recommendation allows more than one channel of each type to be in use. Other Recommendations in the H.332 series include H.323 visual telephone equipment for Local Area Networks, H.225.0 packet and synchronization, H.245
10、 control, H.261 and H.263 video codecs, G.711, G.722, G.728, G.729, and G.723.1 audio codecs, and the T. 120 series of multimedia communications protocols. H.332 terminals are based on Recommendation H.323; therefore, they interwork via gateways with H.310 terminals on B-ISDN, H.320 terminals on N-I
11、SDN, 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. Source ITU-T Recommendation H.332 was prepared by ITU-T Study Group 16 (1997-2000) and was approved under the WTSC Resolution No. 1 proced
12、ure on the 25th of September 1998. COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesSTD-ITU-T RECMN H.332-ENGL 1798 E Lib2591 Db53b32 bL5 m FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in
13、the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. 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 worldwid
14、e basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the IT-T is covered by the
15、procedure laid down in WTSC Resolution No. 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recornmendation, the expression “Adininistrationl is used for conciseness to indicate b
16、oth a telecommunication administration aiid a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concer
17、ning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by
18、 patents, which may be required to implement this Recommendation. However, iinplementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 1998 All rights reserved. No part of this publication may be reproduced
19、 or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. Il Recommendation H.332 (09198) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesSTD-IT
20、U-T RECMN H.332-ENGL 1998 48b2592 flb53b33 55L M CONTENTS Page Scope 1 2 . 3 4 5 6 7 7.1 7.2 7.3 Conference model . 1 4 Nonnative references 4 Definitions 4 Symbols and abbreviations . Conventions 5 Announcement encoding Extensions . Gr ammar . Default records . 8 8 9 9 10 Procedures for conference
21、establishment . Registration . Capability negotiation Announcement Invitation . 8 8.1 8.2 8.3 8.4 Procedures during the conference . Being invited to the panel . Building a roster for an RTP session Joining the panel . Leaving the panel . Periodicity of RTCP SDES items . Generating SSRC in RTP/RTCP
22、10 10 10 11 12 12 12 9 9.1 9.2 9.3 9.4 9.5 9.6 12 10 Security . Mandatory features of H.332 terminals 12 11 13 Bibliography . 12 Recommendation H.332 (09/98) . 111 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesPage Appendix I - Exampl
23、es of SDP announcements . 13 13 I. 1 1.2 Example for distance education 14 14 1.2.1 Public announcement 1.2.2 Private announcement . 16 Example for an RTP/RTCP audio conference using social control . Appendix II - Usage of RSVP . 18 iv Recommendation H.332 (09/98) COPYRIGHT International Telecommuni
24、cations Union/ITU TelecommunicationsLicensed by Information Handling ServicesRecommendation H.332 H.323 EXTENDED FOR LOOSELY COUPLED CONFERENCES (Geneva, 1998) 1 Scope This Recommendation covers highly scalable conferencing on packet-based networks involving hundreds and thousands of participants. T
25、his type of conference is defined in Recommendation H.323 as broadcast and broadcast-panel conferences. This Recommendation is based on Recommendation H.323, thus providing interoperability with circuit-switched endpoints (H.320, H.321, H.324) via Gateways as shown in Figure 1. Use of data, as oppos
26、ed to real-time streams like audio and video, is for further study. Figure 1M.332 - Scope of H.332 conference 2 Conference model The goal of this Recommendation is to provide scalability of the number of terminals in a conference well beyond the limits of Recommendation H.323. Recommendation H.323 i
27、s limited in scalability due to the requirements for tightly coupled conferencing. It requires all participants of the conference to be known and a set of procedures for conference setup, capability negotiation, creation and control of audio/video/data streams, and conference tear down. Such a proce
28、dure for conference setup and capability negotiation at the start of the conference, though essential for tightly coupled conferences, Recommendation H.332 (09/98) 1 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Servicesis cumbersome and impr
29、actical for conferences involving an arbitrarily large number of participants. Information required to setup a large conference must be disseminated well before the start of the conference. Small conferences, like telephone calls, are usually ad hoc in nature. In comparison, large conferences are us
30、ually planned and pre-announced. Examples include presentation to a large geographically dispersed audience, distance learning, etc. When a conference is pre-announced, conference capabilities can also be pre-announced. Some form of capability negotiation is also desirable to accommodate users at di
31、fferent network bandwidth and endpoint resources (Processor power, display resolution, etc.). Network bandwidth may span from low-speed modem links of 14.4 kbit/s to high speed B-ISDN links of 622 Mbit/s. Layered video can be used to accommodate participants at different bandwidth links and their ne
32、ed for varying picture quality. Loosely coupled conferencing is already part of RTP/RTCP. It is designed to scale to thousands of participants. Over a period of time, the identity of each participant is known through the RTCP messages. Floor control is provided through human or social control. Human
33、 control works well for small conferences or in a setting where everybody participating can see each other. But when conferences consist of hundreds of participants, some form of automatic chair-control mechanism is desirable. RTCP is constrained to occupy a small percentage of the total conference
34、bandwidth and any chair-control mechanism implemented in RTCP will not provide service in a timely manner. Therefore, the concept of an H.323 panel is introduced here. The basic model of this Recommendation is shown in Figure 2. The panel consists of a small H.323 conference connected to a large num
35、ber of RTP receiving terminals via RTP/RTCP. These RTP receiving terminals may be H.332 terminals, or other RTP/RTCP capable terminals that have external means to understand how to connect to the conference. Within the panel, full interaction is allowed. Interaction could be through social- or chair
36、- control. Outside the panel, the participants are passive; they are essentially receivers who are, by default, not allowed to interact. If they wish to interact, they have to join the panel or get invited by the panel. Inside the panel, any H.323 model - centralized, decentralized, or hybrid - can
37、be used. However, outside the panel multicast is used in order to provide the scalability required for the H.332 conference. This can be achieved either by using the H.323 decentralized model, or, when the centralized model is used, by using a Multipoint Processor (MP) to multicast media streams to
38、the RTP receiving terminals. The panel consists of permanent and temporary members and is limited in size only by the amount of resources available at the Multipoint Controller (MC) for the conference. The permanent members consist of those who are essential to the conference such as the teacher in
39、a distance-learning virtual class or the presenter in a virtual auditorium full of people. The temporary members come from the RTP receiving terminals who want to participate with questions, discussions, etc. Temporary members change with time as new members join and old members leave voluntarily or
40、 are requested to leave to make room for new ones. The panel employs social or automatic control, If social control is used, then all in the panel can potentially talk and send their video on the audio and video RTP sessions. But, in practice, through social control, one participant usually talks at
41、 a time. Automatic control, on the other hand, is through H.323 chair-control. H.323 chair-control gives special privileges to the chair. Any panel member who wants to talk and send video must first request the floor from the chair. When the floor is granted by the chair, the participant can use the
42、 audio and video RTP sessions. The sequence of events in an H.332 conference is as follows: 1) The conference is pre-announced with sufficient information to enable discovery and participation. The IETF Session Description Protocol (SDP) shall be used to encode the conference announcement. Any mecha
43、nism can be used to carry the announcement. Some suggested mechanisms are: email (SMTP) and web (HTTP). 2 Recommendation H.332 (09/98) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesIf the conference limits participation for security,
44、registration or fee-paying reasons, then the public announcement shall contain information on how to register and obtain a private announcement with the encryption key(s) and algorithm(s), and any other private information. Capability negotiation may be done prior to the conference. If capabilities
45、change, a new announcement shall be created and sent. Even though the capabilities of the conference have been determined prior to the conference, the panel may change the capabilities during the conference. However, changing capabilities during the conference is not advisable as it may force some R
46、TP receiving terminals out of the conference because of the mismatch in capabilities. Before the start of the conference, permanent members of the panel either join or are invited according to the rules of Recommendation H.323. The method through which permanent members are selected is beyond the sc
47、ope of this Recornmendation. The conference starts with a small H.323 panel of permanent members. RTP receiving terminals join the conference to receive streams from the panel. During the conference, RTP receiving terminals may either join the panel or be invited by the panel to participate as tempo
48、rary panel members. The panel participants shall joidleave the H.323 panel according to the rules of Recommendation H.323. The RTP receiving terminals joidleave the conference according to the rules of RTPRTCP. The H.332 conference ends when the H.323 panel conference ends according to the procedure
49、s of Recommendation H.323. j PL (decentralized model shown) I H.245 I IL I I I I I I I I I I-. I I I I I I I I I I l I I I I I r- i+, receiver -1 . -I _ Large RTPTCP-based loosely coupled conference A A A c A RTP/RTCP audio session RTP/RTCP video Session Y I I l I Il I I I I I 11 11 I! 11 11 11 Figure 2LH.332 - A large conference consisting of an H.323 panel and RTPRTCP-based receivers Recommendation H.332 (09/98) 3 - COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling Services3 Normative references The fol
