1、 International Telecommunication Union ITU-T H.221TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2009) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Transmission multiplexing and synchronization Frame structure for a 64 to 1920 kbit/s channel in audiovisual
2、teleservices Recommendation ITU-T H.221 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 H.230H.2
3、39 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 for audiov
4、isual 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 multimedia
5、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 procedures H.56
6、0H.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 middleware H.
7、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.221 (03/2009) i Recommendation ITU-T
8、 H.221 Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices Summary The purpose of Recommendation ITU-T H.221 is to define a frame structure for audiovisual teleservices in single or multiple B or H0channels or a single H11or H12channel which makes the best use of the characte
9、ristics and properties of the audio and video encoding algorithms, of the transmission frame structure and of the existing Recommendations. It offers several advantages: It takes into account of such as Recommendations ITU-T G.704, ITU-T X.30/I.461, etc. It may allow the use of existing hardware or
10、software. It is simple, economic and flexible. It may be implemented on a simple microprocessor using well-known hardware principles. It is a synchronous procedure. The exact time of a configuration change is the same in the transmitter and the receiver. Configurations can be changed at 20 ms interv
11、als. It needs no return link for audiovisual signal transmission, since a configuration is signalled by repeatedly transmitted codewords. It is very secure in case of transmission errors, since the code controlling the multiplex is protected by a double-error correcting code. It allows the synchroni
12、zation of multiple 64 kbit/s or 384 kbit/s connections and the control of the multiplexing of audio, video, data and other signals within the synchronized multiconnection structure in the case of multimedia services such as videoconference. It can be used to derive octet synchronization in networks
13、where this is not provided by other means. It can be used in multipoint configurations, where no dialogue is needed to negotiate the use of a data channel. It provides a variety of data bit rates (from 300 bit/s up to almost 2 Mbit/s) to the user. This revised version of this Recommendation introduc
14、es a number of enhancements and clarifications to the previous version, primarily the description on the usage of Recommendation ITU-T G.719 and Annex C of Recommendation ITU-T G.722.1 (14 kHz audio) in ITU-T H.320 systems. Source Recommendation ITU-T H.221 was approved on 16 March 2009 by ITU-T Stu
15、dy Group 16 (2009-2012) under Recommendation ITU-T A.8 procedures. ii Rec. ITU-T H.221 (03/2009) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommun
16、ication 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 Standardization Assemb
17、ly (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 information technology which
18、 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. Compliance with thi
19、s 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 obligatory languag
20、e 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 implementation of this Rec
21、ommendation 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. As of the date of a
22、pproval of this Recommendation, ITU had 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 urged to consult the TSB p
23、atent 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.221 (03/2009) iii CONTENTS Page 1 Basic principle 1 1.1 Frame alignment signal (FAS) . 1 1.2
24、 Bit-rate allocation signal (BAS) . 3 1.3 Encryption control signal (ECS) 3 1.4 Remaining capacity 3 2 Frame alignment . 3 2.1 General . 3 2.2 Multiframe structure. 4 2.3 Loss and recovery of frame alignment . 6 2.4 Loss and recovery of multiframe alignment. 6 2.5 Procedure to recover octet timing f
25、rom frame alignment 6 2.6 Description of the CRC-4 procedure 7 2.7 Synchronization of multiple connections . 9 3 Bit-rate allocation signal. 10 3.1 Encoding of the BAS 10 3.2 Values of the BAS 11 4 Bit positions for audio, video and data stream . 12 4.1 LSD streams . 12 4.2 Encoded audio streams . 1
26、3 4.3 Encoded video streams . 20 4.4 ISO-encoded audio streams 22 Annex A Definitions and tables of BAS values 26 A.1 Audio command values (000) 29 A.2 Transfer-rate command values (001) 30 A.3 Video, encryption, loop and other commands (010) 31 A.4 LSD/MLP commands (011) . 33 A.5 Audio capabilities
27、 (100) . 35 A.6 Video, MBE and encryption capabilities (101) 35 A.7 Transfer-rate capabilities (100) 36 A.8 LSD/MLP capabilities (101) and other (110). 36 A.9 Escape table values (111) . 37 A.10 HSD/H-MLP/MLP capabilities (Table A.2) 37 A.11 HSD/H-MLP commands (Table A.2). 41 A.12 Au-ISO commands (T
28、able A.2) . 42 A.13 Au-ISO capabilities (Table A.2). 44 A.14 Applications within LSD/HSD channels Capabilities (Table A.4). 45 A.15 Applications within LSD/HSD/MLP/H-MLP channels Commands (Table A.4) . 46 iv Rec. ITU-T H.221 (03/2009) Page A.16 Transfer-rate capabilities and commands used in channel
29、 aggregation (Table A.6) . 46 Annex B Frame structure for interworking between a 64 kbit/s terminal and a 56 kbit/s terminal. 47 B.1 Sub-channel arrangement . 47 B.2 Operation of the 64 kbit/s terminal. 48 B.3 Restriction against some communication modes . 48 B.4 Audio command codes (000) 49 Rec. IT
30、U-T H.221 (03/2009) 1 Recommendation ITU-T H.221 Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices 1 Basic principle This Recommendation provides for dynamically subdividing an overall transmission channel of 64 to 1920 kbit/s into lower rates suitable for audio, video, dat
31、a and telematics purposes. The overall transmission channel is derived by synchronizing and ordering transmissions over from 1 to 6 B-connections, from 1 to 5 H0 connections, or an H11or H12connection. The first connection established is the initial connection and carries the initial channel in each
32、 direction. The additional connections carry additional channels. The total rate of transmitted information is called the “transfer rate“; it is possible to fix the transfer rate less than the capacity of the overall transmission channel (values listed in Annex A). A single 64 kbit/s channel is stru
33、ctured into octets transmitted at 8 kHz. Each bit position of the octets may be regarded as a sub-channel of 8 kbit/s (see Figure 1). The eighth sub-channel is called the service channel (SC), consisting of several parts as described in clauses 1.1 to 1.4. An H0, H11or H12channel may be regarded as
34、consisting of a number of 64 kbit/s time-slots (TS) (see Figure 2). The lowest numbered time-slot is structured exactly as described for a single 64 kbit/s channel, while the other TS has no such structure. In the case of multiple B or H0channels, all channels have a frame structure; that is, the in
35、itial channel controls most functions across the overall transmission, while the frame structure in the additional channels is used for synchronization, channel numbering and related controls. The term “I-channel“ is applied to the initial or only B-channel, to TS1 of initial or only H0channel, and
36、to TS1 of H11, H12channels. 1.1 Frame alignment signal (FAS) This signal structures the I-channel and other framed 64 kbit/s channels into frames of 80 octets each and multiframes (MFs) of 16 frames each. Each multiframe is divided into eight 2-frame sub-multiframes (SMFs). The term “Frame Alignment
37、 Signal“ refers to bits 1-8 of the SC in each frame. In addition to framing and multiframing information, control and alarm information may be inserted in the FAS, as well as error check information to control end-to-end error performance and to check frame alignment validity. Other time-slots are a
38、ligned to the first. The bits are transmitted to line in order, bit 1 first. When an 8 kHz network clock is provided, FAS is transmitted and received in the least significant bit of the octet within each 125 s, e.g., in an ISDN basic or primary rate interface. It should be noted that, where interwor
39、king between the audiovisual terminal and the telephone is required, transmission using the network timing is essential. In the receiver side, FAS should be sought in all bit positions. If received the FAS position conflicts with the network octet timing, the FAS position is given priority. This may
40、 happen when the receiver utilizes network octet timing while the transmitter does not as in a terminal using codecs separate with ISDN terminal adaptor, or when interworking between 64 kbit/s and 56 kbit/s terminals takes place. The FAS can be used to derive receive octet timing when it is not prov
41、ided by the network. However, in the latter case, the terminal cannot transmit FAS with correct alignment into the octet-timed part of the network and cannot intercommunicate with terminals which rely only on network timing for octet alignment. 2 Rec. ITU-T H.221 (03/2009) Bit number 1 2 3 4 5 6 7 8
42、 (SC) 1 Octet number : FAS 8 9 : BAS 16 17 : ECS24 25 Sub-channel #1 Sub-channel #2 Sub-channel #3 Sub-channel #4 Sub-channel #5 Sub-channel #6 Sub-channel #7 Sub-channel #8 80 FAS Frame Alignment Signal BAS Bit-rate Allocation Signal ECS Encryption Control Signal Figure 1 Frame structure of a singl
43、e 64 kbit/s channel (B-channel) 125 s 1 2 3 4 5 6 7 6n2 6n1 6n H0 n = 1 H11 n = 4 H12 n = 5 Audio + service channel 1 2 3 4 5 6 7 8 1 Octet number : FAS 8 9 : BAS 16 17 Sub-channel # 1Sub-channel # 2Sub-channel # 3Sub-channel # 4Sub-channel # 5Sub-channel # 6Sub-channel # 7Sub-channel # 880 Figure 2
44、 Frame structure of higher-rate single channels (H0H11H12 channels) Rec. ITU-T H.221 (03/2009) 3 1.2 Bit-rate allocation signal (BAS) Bits 9-16 of the SC in each frame are referred to as the BAS. This signal allows the transmission of codewords to describe the capability of a terminal to structure t
45、he capacity of the channel or synchronized multiple channels in various ways, and to command a receiver to demultiplex and make use of the constituent signals in such structures. This signal is also used for controls and indications. NOTE For some countries having 56 kbit/s channels, the net availab
46、le bit rates will be 8 kbit/s less. Interworking between a 64 kbit/s terminal and a 56 kbit/s terminal is established according to the frame structure in Annex B. 1.3 Encryption control signal (ECS) Encryption capability requires a dedicated transmission channel. This is provided when required by al
47、locating bits 17-24 of the service channel. This reduces variable data and video transmission rates herein by 800 bit/s. The 800 bit/s is referred to as the ECS channel. 1.4 Remaining capacity The remaining capacity (including the rest of the service channel), carried in bits 1-8 of each octet in th
48、e case of a single 64 kbit/s connection, may convey a variety of signals within the framework of a multimedia service, under the control of the BAS. Some examples follow: voice encoded at 56 kbit/s using a truncated form of PCM of Rec. ITU-T G.711 (A-law or -law); voice encoded at 16 kbit/s and vide
49、o at 46.4 kbit/s; voice encoded at 56 kbit/s with a bandwidth 50 to 7000 Hz (sub-band ADPCM according to Rec. ITU-T G.722); the coding algorithm is also able to work at 48 kbit/s data can then be dynamically inserted at up to 14.4 kbit/s; still pictures coded at 56 kbit/s; data at 56 kbit/s inside an audiovisual session (e.g., file transfer for communicating between personal computers). 2 Frame alignment 2.1 General An 80-octet frame length produces an 80-bit word in the service chann
