1、INTERNATIONAL TELECOMMUNICATION UNION lTU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU H.321 (02/98) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS Infrastructure of audiovisual services - Systems and terminal equipment for audiovisual services Adaptation of H.320 visual telephone terminals to B-
2、ISDN environments ITU-T Recommendation H.321 (Previously CCIlT Recommendation) STD=ITU-T RECMN H-321-ENGL 1998 YB62591 Ob48839 49T = ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS _ Characteristics of transmission channels used for other than telephone purposes Use of telephone-ty
3、pe circuits for voice-frequency telegraphy Telephone circuits or cables used for various types of telegraph transmission or Telephone-type circuits used for facsimile telegraphy Characteristics of data signals H. 1 O-H. I 9 H.20-H.29 H.30-H.39 simultaneous transmission H.40-H.49 H.50-H .99 H. I OO-H
4、. 199 CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS INFRASTRUCTURE OF AUDIOVISUAL SERVICES H.200-H.219 Transmission multiplexing and synchronization H .220-H. 229 Systems aspects H .230-H ,239 Communication procedures H .240-H .259 Coding of moving video H .260-H ,279 Related svstems aspects H 280-H .
5、299 General - Systems and terminal equipment for audiovisual services H.300-H.399 Il For further details, please refer to ITU-T List of Recommendations ITU-T RECOMMENDATION H.321 ADAPTATION OF H.320 VISUAL TELEPHONE TERMINALS TO B-ISDN ENVIRONMENTS Summary This Recommendation describes technical spe
6、cifications for adapting narrow-band audiovisual communications terminals, as defined in Recommendation H.320, to broadband ISDN environments. The terminal conforming to this Recommendation intenvorks with the same type of terminals (i.e. other H.321 terminals) accommodated in B-ISDN as well as exis
7、ting H.320 terminals accommodated in N-ISDN. This revision defines an AAL-5 based stack in addition to the AAL-1 based stack. Source ITU-T Recommendation H.321 was revised by ITU-T Study Group 16 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 6th of February 1998. FORE
8、WORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in 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
9、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, establishes the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations o
10、n these topics. The approval of Recommendations by the Members of the ITU-T is covered by the 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 I
11、n this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY IUGHTS The IT draws attention to the possibility that the practice or implementation of this Recommendation may
12、involve the use of a claimed Intellectual Property Right. The 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. As of the date of approval of t
13、his Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB paten
14、t database. O ITU 1998 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. 11 Recommendation H.321 (02/98) 1 2 3 3.1 3.2 4 4.1 4.2 4.3 4
15、.4 4.5 4.6 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6 6.1 6.2 6.3 6.4 6.5 7 7.1 7.2 CONTENTS Page Scope References Definitions and abbreviations . Definitions Abbreviations . System descnption System configuration Generic terminal architecture . Terminal type Applications Point-to-point communication M
16、ultipoint communication . Infrastructure Audio coding Multimedia multiplexing and synchronization . Video coding End-to-end control Communication procedures AAL functions Call control . Synchronization of 8 kHz timing . ATM Transfer Capability . Terminal equipment Audio source and arrangement . Vide
17、o source and arrangement . Data and other auxiliary equipment Optional enhancements Error resilience . Intercommunications . Intercommunication among H.32 1 terminals . Intercommunication with N-ISDN terminals . 7.2.1 Intercommunication with H.320 . 7.2.2 Intercommunication with telephony Recommenda
18、tion H.321 (02/98) 1 1 6 6 6 6 6 7 7 8 8 8 8 9 9 9 10 . 111 7.3 7.4 Intercommunication between AAL- 1 and AAL-5 Intercommunication with audiovisual terminals connected to other networks Annex A . The use of ATM Adaptation Layer Type 1 . A.l Scope A.2 AAL functions A.2.1 Convergence sublayer function
19、s . A.2.2 SAR sublayer functions . A.2.3 Cell Delay Variation A.3 Call control . A.3.1 Digital connection . A.3.2 Telephony connection . Annex B . The use of ATM Adaptation Layer Type 5 . B.l Scope B.2 Terminal architecture B.3 Network Adaptation Layer . B.3.1 Alignment of octets . Interleaving of t
20、ime slots . Determination of packet size . B.3.2 B.3.3 B.3.4 Optional error handling procedures . B.4 AAL functions B.4.1 Convergence sublayer functions . B.4.2 SAR sublayer functions . Call control . B . 5 B S.1 Digital connection . B.5.2 Telephony connection . Annex C . Alternatives for 8 kHz timi
21、ng of H.321 terminals . C.l Scope C.2 Receiver clock C.3 Transmitter clock C.4 Choosing between adaptive and independent clocks . Page 10 11 11 11 11 11 12 12 12 12 15 16 16 17 17 18 18 18 18 19 19 19 19 19 21 23 23 23 23 24 iv Recommendation H.321 (0298) Recommendation H.321 ADAPTATION OF H.320 VIS
22、UAL TELEPHONE TERMINALS TO B-ISDN ENVIRONMENTS (revised in 1998) 1 Scope This Recommendation describes technical specifications for adapting narrow-band visual telephone terminals, as defined in Recommendation H.320, to broadband ISDN environments. The terminal conforming to this Recommendation inte
23、rworks with the same type of terminals (i.e. other H.321 terminals) accommodated in B-ISDN as well as existing H.320 terminals accommodated in N-ISDN. It is noted that some of the functionalities supported by H.321 terminals are also supported by broadband audiovisual terminals defined in Recommenda
24、tion H.3 1 O. The interworking among H.310, H.321 and H.320 terminals is a mandatory requirement. Intenvorking between H.320 and H.321 terminals is achieved since the different H.321 terminals are defined in terms of the corresponding H.320 terminal types. (See 4.4 for more details.) Intenvorking be
25、tween H.320M.321 and H.310 terminals is achieved through a common set of H.320H.321 functions (defined in Recommendation H.3 1 O). For example, in addition to supporting the Recommendation H.262 video (MPEG-2 video), H.310 terminals shall support Recornmendation H.261 which is part of both Recommend
26、ation H.320 and Recommendation H.321. In H.321 terminals, the adaptation of H.320 functions over B-ISDN is achieved through either ATM Adaptation Layer 1 (AAL-1) or ATM Adaptation Layer 5 (AAL-5). Both Segmentation and Reassembly (SAR) and Convergence Sublayer (CS) functions, as defined in Recommend
27、ations 1.363.1 and 1.363.5, are considered in this Recommendation. H.321 terminals have the same inband functionalities as those supported by H.320 terminals, i.e. as defined in Recommendations H.242, H.230 and H.22 1. Extra broadband-related signalling functions, such as negotiation for the use of
28、the Adaptive Clock Recovery method (asynchronous mode), can be accomplished through 4.293 1 Information Elements as in Annexes A and C. H.321 terminals on the public B-ISDN will conform to Annex A for the use of AAL-1. As an option, they may also operate according to Annex B for the use of AAL-5. H.
29、321 terminals on customer premises networks may operate according to either Annex A or Annex B or both. Intenvorking between AAL-1 and AAL-5 transports shall be accomplished by the use of an AAL- VAAL-5 Intenvorking Unit on the customer premises, as specified in 7.3. 2 References The following ITU-T
30、 Recommendations and other references contain provisions which, 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; all users of this Recommendat
31、ion are therefore encouraged to investigate the possibility of 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. - ITU-T Recommendation H.221 (1997), Frame structurefor a 64 to 1920 k
32、bit/s channel in audiovisual telesewices. Recommendation H.321 (02/98) 1 ITU-T Recommendation H.230 (1 997), Frame-synchronous control and indication signals for audiovisual systems. ITU-T Recommendation H.242 (1 997), System for establishing communication between audiovisual terminals using digital
33、 channels up to 2 Mbith. ITU-T Recommendation H.243 (1 997), Procedures for establishing communication between three or more audiovisual terminals using digital channels up to 1920 kbith. ITU-T Recommendation H.26 1 (1 993), Video codec for audiovisual services at p x 64 kbith. ITU-T Recommendation
34、H.3 1 O (1 996), Broadband audiovisual communication systems and terminals. ITU-T Recommendation H.320 (1 997), Narrow-band visual telephone systems and terminal equipment. ITU-T Recommendation H.322 (1 996), Visual telephone systems and terminal equipment for local area network which provide a guar
35、anteed quality of service. ITU-T Recommendation 1.356 (1 996), B-ISDN ATM layer cell transfer performance. ITU-T Recommendation 1.361 (1 995), B-ISDN ATM layer speczjcation. ITU-T Recommendation 1.363.1 (1 996), B-ISDN ATM Adaptation Layer speclfication: Type 1 AAL. ITU-T Recommendation 1.363.5 (1 9
36、96), B-ISDN ATM Adaptation Layer speczjication: Type 5 AAL. ITU-T Recommendation 1.371 (1996), Trafic control and congestion control in B-ISDN. ITU-T Recommendation 1.41 3 (1 993), B-ISDN user-network interface. ITU-T Recommendation 1.5 80 (1 995), General arrangements for interworking between B-ISD
37、N and 64 kbith based ISDN. ITU-T Recommendation Q.293 1 (1 995), B-ISDN Digital Subscriber Signalling System No. 2 - User-Network Interface (UN4 layer 3 specijication for basic caWconnection control. Definitions and abbreviations 3.1 Definitions This Recommendation defines the following terms: 3.1.1
38、 3.1.2 3.1.3 3.1.4 provided as a single B/H,/H,/H,-channel or a multiple of B/HO-channels. 3.1.5 N-ISDN or equivalent channel in B-ISDN. broadband: Bit rate including and beyond that of narrow-band. circuit emulation: Emulation of the N-ISDN circuit-switched service by B-ISDN. inband signalling: Sig
39、nalling via BAS of the H.221 frame structure. narrow-band: Bit rate ranging from 64 kbitk to 1920 kbit/s. This channel capacity is outband signalling: Signalling via a subchannel not part of the B/H,/H,-channel in 2 Recommendation H.321 (02198) STDmITU-T RECMN H.321-ENGL 1998 4862591 Ob48846 62T 3.2
40、 Abbreviations This Recommendation uses the following abbreviations: AAL ATM BCH B-ISDN B-NT B-TA B-TE C and b) access signalling interworking between N-ISDN and B-ISDN. 5 Other Q.293 1 messages may also use these IEs. 12 Recommendation H.321 (02/98) Table A.lA3.321- 4.2931 information elements - Di
41、gital connection over AAL-1 Information element parameter(s) Parameter value(s) for H.321 terminals for digital connection over AAL1 Q.2931 information element Narrow-band Bearer Information transfer capability Unrestricted DigitaInformation (UDI) Restricted Digital Information (RI) UD1 with tone/an
42、nouncement (UDI-TA) Capability (N-BC) Circuit Transfer mode Information transfer rate 64 kbit/s 2 x 64 kbit/s 384 kbit/s 1536 kbit/s 1920 kbit/s Multirate (64 kbits base rate) Rate multiplier 2 to the maximum number of B-channels User information layer 1 protocol Recommendations H.221 and H.242 Bear
43、er class BCOB-A Broadband Bearer Capability (B-BC) Susceptibility to clipping Susceptible to clipping Call configuration Point-to-point (Variable: depends on the transfer rate) Forward peak cell rate (for CLP Ot-1) Backward peak cell rate (for CLP 0+1) ATM traffic descriptor AAL parameters AAL-1 Cir
44、cuit Transport Subtype identifier CBR rate 64 kbit/s n x 64 kbits 2 to the maximum value of n (in n x 64 kbit/s) supported by the H.321 terminal (Note 1) Null (synchronous) Adaptive Clock Method (Note 2) Multiplier Source clock frequency recovery method Error correction method Null (no error correct
45、ion is provided) (Note 3) (Note 4) Structure data transfer block size Partially filled cells method 47 (Under study) Cumulative transit delay value End-to-end transit delay Maximum end-to-end transit delay value Recommendation H.321 (02/98) 13 STDVITU-T RECMN H-321-ENGL 1778 4862573 Ob48857 405 Info
46、rmation element parameter(s) Table A.lm.321- Q.2931 information elements - Digital connection over AAL-1 (continued) Parameter value) for H.321 terminals for digital connection over AAL-1 4.2931 information element Quality of Service (QOS) Narrow-band Low Layer Compatibility (N-LLC) (Note 5) Narrow-
47、band High Layer Compatibility OI-HLC) OAM traffic descriptor Information transfer capability Negotiation indicator Transfer mode Information transfer rate Rate multiplier User information layer 1 protocol (Under study) Unrestricted Digital Information (UDI) Restricted Digital Information (RDI) UD1 w
48、ith tone/announcement (UDI-TA) Out-band negotiation not possible Out-band negotiation possible Circuit 64 kbit/s 2 x 64 kbit/s 384 kbit/s 1536 kbits 1920 kbits Multirate (64 kbit/s base rate) 2 to the maximum number of B-channels Recommendations H.22 1 and H.242 (Note 6) (Under study) NOTE 1 - It is
49、 important to note that, when H.321 terminals are communicating with H.320 terminals, then the multipliers 6,24 and 30 shall be used for the Ho, Hii, and H, transfer rates, respectively. On the other hand, when H.321 terminals are communicating among themselves over a B-ISDN network, then all integer values between 2 and 30 can be used, subject to any limitation of H.22 1 BAS codes for allowed information transfer rates. NOTE 2 - There are two possible solutions for recovering the source clock in H.32 1 terminals: 1) if a common clock is available at
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