1、 International Telecommunication Union ITU-T H.242TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2009) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Communication procedures System for establishing communication between audiovisual terminals using digital ch
2、annels up to 2 Mbit/s Recommendation ITU-T H.242 ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS H.100H.199 INFRASTRUCTURE OF AUDIOVISUAL SERVICES General H.200H.219 Transmission multiplexing and synchronization H.220H.229 Systems aspects
3、 H.230H.239 Communication procedures H.240H.259 Coding of moving video H.260H.279 Related systems aspects H.280H.299 Systems and terminal equipment for audiovisual services H.300H.349 Directory services architecture for audiovisual and multimedia services H.350H.359 Quality of service architecture f
4、or audiovisual and multimedia services H.360H.369 Supplementary services for multimedia H.450H.499 MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definitions, protocols and procedures H.500H.509 Mobility for H-Series multimedia systems and services H.510H.519 Mobile mu
5、ltimedia collaboration applications and services H.520H.529 Security for mobile multimedia systems and services H.530H.539 Security for mobile multimedia collaboration applications and services H.540H.549 Mobility interworking procedures H.550H.559Mobile multimedia collaboration inter-working proced
6、ures H.560H.569 BROADBAND, TRIPLE-PLAY AND ADVANCED MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 Advanced multimedia services and applications H.620H.629 IPTV MULTIMEDIA SERVICES AND APPLICATIONS FOR IPTV General aspects H.700H.719 IPTV terminal devices H.720H.729 IPTV midd
7、leware H.730H.739 IPTV application event handling H.740H.749 IPTV metadata H.750H.759 IPTV multimedia application frameworks H.760H.769 IPTV service discovery up to consumption H.770H.779 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T H.242 (03/2009) i Recommendat
8、ion ITU-T H.242 System for establishing communication between audiovisual terminals using digital channels up to 2 Mbit/s Summary Videophone, videoconferencing and other conversational multimedia services on fixed bit-rate networks (such as ISDN) depend on the multiplex structure described in Recomm
9、endation ITU-T H.221. The control channel within this multiplex is the so-called bit-rate allocation signal (BAS) position in each frame. This Recommendation describes all the point-to-point procedures involving the BAS codes: initial capability exchange and mode initialization, including restricted
10、-network operation; in-session mode switching, including audiovisual mode changes and activation of data channels; other procedures, including single/multiple channel interconnection, encryption, mode-preference indication, conveyance of network addresses and use of BAS extension codes. This revised
11、 version of Recommendation ITU-T H.242 introduces a number of enhancements and clarifications to the previous version, primarily the description on the usage of G.719 and Annex C of Recommendation ITU-T G.722.1 (14 kHz audio) in H.320 systems. Source Recommendation ITU-T H.242 was approved on 16 Mar
12、ch 2009 by ITU-T Study Group 16 (2009-2012) under Recommendation ITU-T A.8 procedure. ii Rec. ITU-T H.242 (03/2009) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs).
13、 The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. 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 Sta
14、ndardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of informati
15、on technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
16、Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other
17、 obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or impleme
18、ntation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
19、As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urg
20、ed to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2009 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T H.242 (03/2009) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitio
21、ns and conventions . 2 4 Abbreviations and acronyms 3 5 Terminal capabilities 3 5.1 Audio capabilities. 4 5.2 Video capabilities . 7 5.3 Transfer rate capabilities 30 5.4 Data capabilities . 30 5.5 Terminals on restricted networks: capability . 30 5.6 Encryption and extension-BAS capabilities. 30 5.
22、7 Null capability 30 6 Transmission. 30 6.1 Transmission modes . 30 6.2 Establishment of compatible modes of operation 31 7 Frame structure . 31 8 Basic sequences for in-channel procedures 32 8.1 Capability exchange sequence A 32 8.2 Mode switching sequence B. 36 8.3 Frame reinstatement sequence C 3
23、6 9 Mode initialization, dynamic mode switching and Mode 0 forcing. 37 9.1 Mode initialization procedure. 37 9.2 Dynamic mode switching (see Figure 2) 39 9.3 Mode 0 forcing procedure 41 9.4 Mode mismatch recovery procedure 43 9.5 Procedure for influencing the mode transmitted from remote endpoint 43
24、 10 Recovery from fault conditions 43 10.1 Unexpected loss of synchronization or frame alignment . 44 10.2 Recovery from loss of connection(s) 44 11 Network consideration: call connection, disconnection and call transfer 45 11.1 Call connection. 45 11.2 Terminal disconnection 46 11.3 Call transfer 4
25、7 11.4 Conferencing 47 12 Procedure for activation and de-activation of data channels 47 12.1 General . 47 12.2 Procedures applicable to all data types. 47 iv Rec. ITU-T H.242 (03/2009) Page 12.3 Equipment capable of operating using protocol according to Recommendation ITU-T T.120 48 12.4 Data equip
26、ment not conforming to Recommendation ITU-T T.120 48 12.5 Dummy data . 49 13 Procedures for operation in restricted networks . 49 13.1 Network aspects 49 13.2 Terminal-network configurations and properties . 50 13.3 Transmission formats . 52 13.4 Procedures 52 14 Procedure for use of BAS-extension c
27、odes 60 15 Bit occupancy and the sequencing of BAS codes 61 16 Procedure for dealing with single/multiple channel interconnection . 64 17 Procedure for use of encryption control signal channel . 64 18 Transmission of network addresses 65 18.1 Address of initial connection 65 18.2 Addresses of additi
28、onal connections 65 19 Informative codes . 67 19.1 Recommendation version identification. 67 19.2 Manufacturer/type identification 67 Appendix I Initialization: Case of videophone to Recommendation ITU-T H.320, type Xb . 68 Appendix II Mode-0 forcing: Case of videophone to Recommendation ITU-T H.320
29、, type Xb . 72 Appendix III Example of use of message structure 74 III.1 Initial capability exchange, including MBE-cap 74 III.2 Subsequent capability exchange, including MBE capability message. 74 III.3 Mode switch to non-standard mode using MBE command . 75 Appendix IV Examples of symmetrical and
30、asymmetrical transmission modes 76 IV.1 Example of symmetrical transmission mode 76 IV.2 Example of asymmetrical transmission mode 76 IV.3 Example of unsymmetrical video mode . 76 Appendix V Examples relating to data transmissions 77 V.1 Transfer-rate 1B, audio at 48 kbit/s, no video or video off 77
31、 V.2 Transfer-rate 1B, audio at 16 kbit/s, no video or video off 77 V.3 Transfer-rate 1B, audio at 16 kbit/s, video on 77 V.4 Transfer-rate 2B, audio at 48 kbit/s, video on 77 V.5 Transfer-rate 2B, audio at 16 kbit/s, video on 78 Appendix VI Hierarchical capability BAS codes . 79 Rec. ITU-T H.242 (0
32、3/2009) v Page Appendix VII Interpretation of received audio capability BAS codes . 81 Appendix VIII Examples of legal and illegal capability BAS sequences. 82 Appendix IX. 84 Appendix X An algorithm to determine whether an incoming bit stream was encoded by -law or A-law PCM . 88 X.1 Basic determin
33、ation algorithm . 88 X.2 Possible extensions and refinements 89 Bibliography. 90 Rec. ITU-T H.242 (03/2009) 1 Recommendation ITU-T H.242 System for establishing communication between audiovisual terminals using digital channels up to 2 Mbit/s 1 Scope This Recommendation should be associated with ITU
34、-T H.221 and ITU-T H.230. A number of applications utilizing narrow-band (3 kHz) and wideband (7 kHz) speech together with video and/or data have been identified, including high quality telephony, audio and videoconferencing (with or without various kinds of telematic aids), audiographic conferencin
35、g, and so on. More applications will undoubtedly emerge in the future. To provide these services, a scheme is recommended in which a channel accommodates speech, and optionally video and/or data at several rates, in a number of different modes. Signalling procedures are required to establish a compa
36、tible mode upon call set-up, to switch between modes during a call and to allow for call transfer. Some services will require only a single channel which could, according to the procedures in this Recommendation, be B (64 kbit/s), H0(384 kbit/s), H11(1536 kbit/s) or H12(1920 kbit/s). Other services
37、will require the establishment of two or more connections providing B or H0channels: in such cases the first established is called hereafter the initial channel while the others are called additional channels. Unless otherwise specified, all references to frame alignment signal (FAS) bit-rate alloca
38、tion signal (BAS) and service channel (SC) refer to the initial channel or, in the case of a higher-order channel, to the time-slot No. 1 of this channel. All audio and audiovisual terminals using G.722 audio coding and/or G.711 speech coding or other standardized audio codings at lower bit rates sh
39、ould be compatible to permit connection between any two terminals. This implies that a common mode of operation has to be established for the call. The initial mode might be the only one used during a call or, alternatively, switching to another mode can occur as needed depending on the capabilities
40、 of the terminals. Thus, for these terminals, an in-channel procedure for dynamic mode switching is required. The following clauses develop these considerations and describe recommended in-channel procedures. 2 References The following ITU-T Recommendations and other references contain provisions wh
41、ich, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of
42、applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. I
43、TU-T G.719 Recommendation ITU-T G.719 (2008), Low-complexity full-band audio coding for high-quality conversational applications. ITU-T H.221 Recommendation ITU-T H.221 (2004), Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices. ITU-T H.224 Recommendation ITU-T H.224 (2000),
44、 A real time control protocol for simplex applications using the H.221 LSD/HSD/MLP channels. 2 Rec. ITU-T H.242 (03/2009) ITU-T H.230 Recommendation ITU-T H.230 (2004), Frame-synchronous control and indication signals for audiovisual systems. ITU-T H.241 Recommendation ITU-T H.241 (2003), Extended v
45、ideo procedures and control signals for H.300-series terminals. ITU-T H.243 Recommendation ITU-T H.243 (2000), Procedures for establishing communication between three or more audiovisual terminals using digital channels up to 1920 kbit/s. ITU-T H.244 Recommendation ITU-T H.244 (1995), Synchronized a
46、ggregation of multiple 64 or 56 kbit/s channels. ITU-T H.245 Recommendation ITU-T H.245 (2008), Control protocol for multimedia communication. ITU-T H.261 Recommendation ITU-T H.261 (1993), Video codec for audiovisual services at p 64 kbit/s. ITU-T H.262 Recommendation ITU-T H.262 (2000) | ISO/IEC 1
47、3818-2:2000, Information technology Generic coding of moving pictures and associated audio information: Video. ITU-T H.263 Recommendation ITU-T H.263 (2005), Video coding for low bit rate communication. ITU-T H.264 Recommendation ITU-T H.264 (2003), Advanced video coding for generic audiovisual serv
48、ices. ITU-T T.120 Recommendation ITU-T T.120 (1996), Data protocols for multimedia conferencing. ISO/IEC 14496-3 ISO/IEC 14496-3:2005, Information technology Coding of audio-visual objects Part 3: Audio. 3 Definitions and conventions This Recommendation defines the following terms: 3.1 H.221 frame s
49、tructure; H.221 framing: Frame structure according to ITU-T H.221. 3.2 T.120 protocol: See ITU-T T.120. 3.3 capset: Abbreviation for “Capability set“. 3.4 calling end: Endpoint which requests the first 64/56-channel connection of the whole session, resulting in the establishment of the “initial channel“. If, during fault-recovery procedures, the initial channel is transferred to another connection, this does not affect the definition. 3.5 called end: Endpoint which accepts the first 64/56-channel co
