1、 International Telecommunication Union ITU-T H.224TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2005) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Transmission multiplexing and synchronization A real time control protocol for simplex applications using the
2、 H.221 LSD/HSD/MLP channels ITU-T Recommendation H.224 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 a
3、spects 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 architec
4、ture for 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 Mob
5、ile multimedia 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
6、procedures H.560H.569 BROADBAND AND TRIPLE-PLAY MULTIMEDIA SERVICES Broadband multimedia services over VDSL H.610H.619 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. H.224 (01/2005) i ITU-T Recommendation H.224 A real time control protocol for simplex applications
7、 using the H.221 LSD/HSD/MLP channels Summary This Recommendation provides a simple yet flexible protocol for simplex, low delay applications such as far end camera control and text conversation using the LSD, HSD, and MLP channels defined in ITU-T Recs H.221 and H.243. This 2004 revised version add
8、s a Generic Capability Object Identifier in clause 11, which enables the use of the H.224 protocol with systems according to ITU-T Rec. H.245. Source ITU-T Recommendation H.224 was approved on 8 January 2005 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T R
9、ec. H.224 (01/2005) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and t
10、ariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Reco
11、mmendations 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 fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recomm
12、endation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperabi
13、lity or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that comp
14、liance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validit
15、y 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, ITU had not received notice of intellectual property, protected by patents, which may be require
16、d 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 patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, withou
17、t the prior written permission of ITU. ITU-T Rec. H.224 (01/2005) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations 3 5 Conventions 3 6 Relationship to other Recommendations 4 6.1 Relationship to Recommendation H.221 4 6.2 Relationship to T.120 protocols . 5 7 Major feature
18、s. 5 7.1 Physical layer transmission over H.221 . 6 7.2 Client Data Block segmentation. 6 7.3 Terminal address resolution . 7 7.4 Client ID assignments. 7 7.5 Data layer protocol frame structure 8 8 Field descriptions 9 9 Client Management Entity 10 9.1 CME Client List Message 10 9.2 CME Extra Capab
19、ilities Message. 11 9.3 CME Client List Command 11 9.4 CME Extra Capabilities Command 11 9.5 CME standard command codes 12 9.6 CME standard response codes 12 10 List of Standard Clients IDs . 13 10.1 Extended Client IDs . 13 10.2 Non-Standard Client IDs 13 11 Generic Capability Object Identifier 14
20、ITU-T Rec. H.224 (01/2005) 1 ITU-T Recommendation H.224 A real time control protocol for simplex applications using the H.221 LSD/HSD/MLP channels 1 Scope This Recommendation covers the frame structure, elements of procedure and formats to support a real time control (ITU-T Rec. H.224) protocol prim
21、arily used in multipoint videoconference networks using the H.243 broadcast capability of the H.221 LSD/HSD channels or the H.221 MLP data channel. H.224 frames are encapsulated in Q.922 Unnumbered Information (UI) frames, referred to as I mode for the remainder of this Recommendation. This protocol
22、 is intended to be used by Recommendations that describe applications that require the real-time H.224 services, limited at this time to far end camera control but potentially including other real-time applications. This protocol serves to provide low-cost, low-latency and low delay broadcast servic
23、es for applications that do not require reliable, flow-controlled links. This Recommendation is not intended for use by applications such as those specified in the T-series, e.g., JPEG image distribution that requires reliable links. This protocol allows for multiplexing of one or more datagram stre
24、ams over the H.221 LSD, HSD or MLP channels. Data transfer is always by way of Q.922 UI frames using fixed DLCI assignment. The data link protocol contains network layer information using unique source and destination terminal addresses, conveyed to the terminal via the TIA symbol as described in IT
25、U-T Recs H.230 and H.243. The block diagram in Figure 1 illustrates the location of the data link protocol in H.221 communications architecture. The interface between the client and the data link layer is beyond the scope of this Recommendation, and is left to the discretion of the manufacturers. 2
26、References The following ITU-T 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;
27、 users of this Recommendation 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. The reference to a document within this Reco
28、mmendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T Recommendation H.221 (2004), Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices. ITU-T Recommendation H.243 (2000), Procedures for establishing communication between three or more a
29、udiovisual terminals using digital channels up to 1920 kbit/s. ITU-T Recommendation Q.922 (1992), ISDN data link layer specification for frame mode bearer services. ITU-T Recommendation T.122 (1998), Multipoint communication service Service definition. ITU-T Recommendation T.123 (1999), Networks-spe
30、cific data protocol stacks for multimedia conferencing. ITU-T Recommendation T.125 (1998), Multipoint communication service protocol specification. 2 ITU-T Rec. H.224 (01/2005) ITU-T Recommendation T.140 (1998), Protocol for multimedia application text conversation. ISO/IEC 3309:1993, Information te
31、chnology Telecommunications and information exchange between systems High-level data link control (HDLC) procedures Frame structure. Figure 1/H.224 Block diagram of real time control protocol 3 Definitions This Recommendation defines the following terms: 3.1 BROADCAST value: The Terminal address val
32、ue, which specifies all connected terminals in a conference. For all data channels, the BROADCAST value is 0x0000. 3.2 channel: One of the H.221 data channels, LSD (low speed data), HSD (high speed data), or MLP (multilayer protocol). Note that MLP and H-MLP are aggregated to form a single data chan
33、nel as specified in ITU-T Rec. T.123. 3.3 client: An entity that uses the data transfer services of the Data Link layer. An example of a Client is Far End Camera Control. 3.4 client data block: A unit of data submitted at the H.224 Client Interface. If the H.224 segments a Client Data Block before t
34、ransmission, the remote terminal must receive all segments (in numerical order) before submitting the reconstructed Client Data Block to the destination client. The maximum length of a Client Data Block is 1024 octets. 3.5 client ID: A unique identification number used when sending data to a specifi
35、c client. Clients that are standardized for use in generic applications are allocated Standard Client IDs (listed in ITU-T Rec. H.224). Client IDs also may be assigned for non-standard or proprietary applications using the manufacturer specific mechanism described. 3.6 client management entity: A da
36、ta link client that uses Client ID 0x00 to send a complete list of locally registered clients and their optional extra capabilities. 3.7 HDLC frame format: As specified in ISO/IEC 3309. ITU-T Rec. H.224 (01/2005) 3 3.8 high priority data: Client Data Blocks that require a low transmission time laten
37、cy and/or low transmission time variability. 3.9 low priority data: Client Data Blocks that are part of a large data transfer that requires maximum bandwidth efficiency to minimize the total time to complete the transfer. 3.10 MLP channel: A H.221 channel in which H.224 and/or the T.120-series proto
38、cols are run. 3.11 MLP compatibility mode: An H.224 operation mode, which uses the MLP channel to transfer data. H.224 data sent on the MLP channel is broadcast to all other H.224 capable terminals. 3.12 simplex protocol: A communication protocol that is purely one-way, and where acknowledgements ar
39、e not part of any application protocol. Error control is either not present, or is accomplished via forward error correction. 3.13 ITU-T Recommendation T.120: The overview Recommendation for the T-series Recommendations. This is similar to the fashion in which ITU-T Rec. H.320 describes terminal equ
40、ipment conforming to the H-series Recommendations. 3.14 T.120 protocols: A suite of protocols, including T.122, T.123, T.124, T.125 and others that provide multipoint, reliable data transfer and application coordination for conferencing applications. 3.15 UI-mode: A mode of operation in which the H.
41、224 protocol is encapsulated within the information field of Q.922 UI frames for multipoint applications (see Figure 2). 4 Abbreviations This Recommendation uses the following abbreviations: BECN Backward Explicit Congestion Notification (ITU-T Rec. Q.922) BS Beginning Segment CME Client Management
42、Entity DE Discard Eligibility Indicator (ITU-T Rec. Q.922) DLCI Data Link Connection Identifier (ITU-T Rec. Q.922) EA Address Field Extension Bit (ITU-T Rec. Q.922) ES Ending Segment FCS Frame Check Sequence FECN Forward Explicit Congestion Notification HDLC High-level Data Link Control LSB Least Si
43、gnificant Bit MCU Multipoint Control Unit MSB Most Significant Bit UI frame Unnumbered Information frame 5 Conventions Channel Refers to the LSD channel, the HSD channel, the MLP channel or the aggregated MLP/H-MLP channel. BROADCAST value Always refers to the value 0x0000 when used in place of the
44、terminal address to indicate a request to broadcast the packet to all conference members. Equipment Refers to both terminals and MCUs. 4 ITU-T Rec. H.224 (01/2005) ID Short for identifier. “Shall“ Used in this Recommendation to specify a mandatory requirement. “Should“ Used in this Recommendation to
45、 specify a suggested but not required course of action. 6 Relationship to other Recommendations 6.1 Relationship to Recommendation H.221 6.1.1 H.224 capabilities H.224-LSD: The H.224 equipment is capable of operating on the LSD channel, including turning H.224 on and off. This capability is mandator
46、y for H.224 terminals and optional for H.224 MCUs. The H.224 operation on both LSD and the HSD channels at the same time is for further study. H.224-MLP: The H.224 equipment is capable of operating on the MLP channel as described in 6.2, including turning H.224 on and off. This capability is mandato
47、ry for H.224 terminals and optional for H.224 MCUs. If an MCU has this capability, it shall broadcast any UI frames it receives on the MLP channel from one terminal to all other terminals in the conference as required by ITU-T Rec. H.224. The presence of this capability in a terminal does not imply
48、the support of the T.120 protocols. H.224-HSD: The H.224 equipment is capable of operating on an HSD channel, including turning H.224 on and off. This capability is optional for H.224 terminals and MCUs. The H.224 operation on both the LSD and the HSD at the same time is for further study. H.224-sim
49、: The H.224 equipment is capable of simultaneously operating H.224 in the LSD channel and T.120 protocols in the MLP channel. Thus, H.224-sim capability equipment can both: a) open allowed combinations of LSD and MLP channels; and b) simultaneously run H.224 in LSD and T.120 protocols in MLP. This capability is optional for H.224 equipment. 6.1.2 H.224 commands H.224 procedures apply to these commands: H.224-LSD-on: Used to indicate the start of H.224 operation on the open LSD channel. This command shall be ign
