1、 International Telecommunication Union ITU-T H.248.20TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2013) SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMSInfrastructure of audiovisual services Communication procedures Gateway control protocol: The use of Local and Remote Descriptors with ITU-T H.22
2、1 and ITU-T H.223 multiplexing Recommendation ITU-T H.248.20 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 Sys
3、tems aspects H.230H.239 Communication procedures H.240H.259Coding 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 arc
4、hitecture 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.51
5、9 Mobile 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.559 Mobile multimedia collaboration inter-wo
6、rking procedures 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 Ubiquitous sensor network applications and Internet of Things H.640H.649 IPTV MULTIMEDIA SERVICES AND APPLIC
7、ATIONS FOR IPTV General aspects H.700H.719 IPTV terminal devices H.720H.729 IPTV middleware 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 Digital Signage H.780H.789
8、For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T H.248.20 (03/2013) i Recommendation ITU-T H.248.20 Gateway control protocol: The use of Local and Remote Descriptors with ITU-T H.221 and ITU-T H.223 multiplexing Summary Recommendation ITU-T H.248.20 defines how the
9、Local and Remote Descriptors are used within ITU-T H.248, ITU-T H.221 and ITU-T H.223 multiplexing (MUX) terminations to associate demultiplexed streams (logical channels) with ITU-T H.248.1 streams. This revision incorporates updates the allowed media values to align with the latest version of the
10、Session Description Protocol (SDP). History Edition Recommendation Approval Study Group 1.0 ITU-T H.248.20 2002-11-29 16 2.0 ITU-T H.248.20 2013-03-16 16 ii Rec. ITU-T H.248.20 (03/2013) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of
11、 telecommunications, information and communication technologies (ICTs). 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 t
12、elecommunications 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 Recommendations on these topics. The approval of ITU-T Recommendations is covered by t
13、he 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 Recommendation, the expression “Administration“ is used for conciseness to indicate both
14、 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., interoperability or applicability) and compliance with the Recommendation is achieved when a
15、ll 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 compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY R
16、IGHTS 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, validity or applicability of claimed Intellectual Property Rights, whether asserted by
17、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 required to implement this Recommendation. However, implementers are cautioned that thi
18、s may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2013 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-
19、T H.248.20 (03/2013) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Logical channel parameters within the MUX termination . 2 5.1 Text encoding . 2 5.2 Binary encoding 3 6 Example 3 6.1 Context model 4 6.2 The media descriptor for the TDM termin
20、ation . 4 6.3 The multiplex descriptor for the MUX termination . 4 6.4 The media descriptor for the MUX termination . 4 6.5 The media descriptor for the RTP termination . 5 Rec. ITU-T H.248.20 (03/2013) 1 Recommendation ITU-T H.248.20 Gateway control protocol: The use of Local and Remote Descriptors
21、 with ITU-T H.221 and ITU-T H.223 multiplexing 1 Scope This Recommendation defines how ITU-T H.248.1 Local and Remote Descriptors are coded in the case of the use of ITU-T H.221 and ITU-T H.223 multiplexes. Figure 1 shows the scope of this Recommendation. H.248.20_F01ContextMedia gatewayStream 1Stre
22、am 3Stream 2H.221/H.223Scope of RecommendationCircuitterminationMultiplex terminationPacketterminationLogical channelnumbersFigure 1 Scope of this Recommendation 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute
23、 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 applying the most recent edition of the Recomme
24、ndations 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. ITU-T H.221 Recommendation ITU-T H.221 (2009), F
25、rame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices. ITU-T H.223 Recommendation ITU-T H.223 (2001), Multiplexing protocol for low bit rate multimedia communication. ITU-T H.245 Recommendation ITU-T H.245 (2011), Control protocol for multimedia communication. ITU-T H.248.1 Reco
26、mmendation ITU-T H.248.1 (2013), Gateway control protocol: Version 3. ITU-T H.324 Recommendation ITU-T H.324 (2009), Terminal for low bit-rate multimedia communication. IETF RFC 3550 IETF RFC 3550 (2003), RTP: A Transport Protocol for Real-Time Applications. 2 Rec. ITU-T H.248.20 (03/2013) IETF RFC
27、4566 IETF RFC 4566 (2006), SDP: Session Description Protocol. 3 Definitions None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ABNF Augmented Backus-Naur Form LCN Logical Channel Number MG Media Gateway MGC Media Gateway Controller MUX Multiplex PER
28、 Packed Encoding Rules RTP Real-time Transport Protocol SDP Session Description Protocol TDM Time Division Multiplex 5 Logical channel parameters within the MUX termination Every demultiplexed ITU-T H.221 and ITU-T H.223 media stream is associated with an ITU-T H.248.1 Stream. For each ITU-T H.248.1
29、 stream, a Stream Descriptor is defined within the MUX termination. The Logical Channel Number (LCN) values for the ITU-T H.221 and ITU-T H.223 media streams are defined in the Local and Remote Descriptors. Which descriptor is used depends on the media direction of the logical channel defined by a s
30、pecific LCN (different LCN values may be used in each media direction of the logical channel). The Local Descriptor defines the media flowing in to the multiplexer, and the value in the Remote Descriptor defines the media flowing out from the multiplexer. If either descriptor is not defined, the med
31、ia stream flow is not activated for the specific direction. A descriptor MAY be added later during the session (using the ITU-T H.248.1 Modify command) or the media stream is unidirectional. If the ITU-T H.221 and ITU-T H.223 media stream is bidirectional, both the Local and Remote Descriptors MUST
32、be defined, even if the LCN value, codecs etc. are the same in both media stream directions. For the ITU-T H.248.1 Stream associated with the ITU-T H.245 control stream (LCN 0), only the Local Descriptor (e.g., if the control stream is not associated with an ITU-T H.248.1 Stream which also is define
33、d elsewhere within the Context) may be used, even if the control stream is bidirectional. If the demultiplexed streams are forwarded to a packet network (e.g., IP network, transported using the Real-time Transport Protocol (RTP), the payload types, etc. (i.e., for the IP port) are defined within the
34、 ephemeral packet termination. The payload type values may, or may not, be the same within the multiplexed ITU-T H.221 and ITU-T H.223 stream and within the demultiplexed packet streams. 5.1 Text encoding According to ITU-T H.248.1, the stream Local and Remote Descriptors contain SDP. As such, SDP i
35、s required to describe how the stream maps to an ITU-T H.245 Logical Channel Number. The use of SDP for the ITU-T H.245 control stream is optional, since the LCN value MUST be 0 by default. The clauses below describe the necessary SDP syntax and values to describe this mapping for the ITU-T H.221 an
36、d ITU-T H.223 Multiplex termination. Rec. ITU-T H.248.20 (03/2013) 3 5.1.1 “c=line“ Line for H.221 and H.223 MUX termination The syntax of the connection field: connection-field = “c=“ nettype SP addrtype SP connection-address CRLF The value of nettype is “H221“ or “H223“. The value of addrtype is “
37、. The value of connection-address is irrelevant, so any value which is allowed according to the ABNF rules can be used. This Recommendation uses the “ value. 5.1.2 “m=line“ Line for ITU-T H.221 and ITU-T H.223 MUX termination The syntax of the media field: media-field = “m=“ media SP port “/“ intege
38、r SP proto 1*(SP fmt) CRLF The possible media values for media are “audio“, “video“, “data“ and “application“, depending on the media type within the specific ITU-T H.248.1 Stream. Value “application“ is used if a Stream is defined for the demultiplexed ITU-T H.245 messages. NOTE Some older applicat
39、ions may use the value “control“. To aid interoperability MGs should be able to recognize “control“. The value of port defines the ITU-T H.221 and ITU-T H.223 Logical Channel Number (LCN) associated with the ITU-T H.248.1 stream defined in the Local or Remote Descriptor (depending on the media flow
40、direction) for that specific ITU-T H.248.1 stream. The use of the optional “/“ integer parameter in the ITU-T H.221 and ITU-T H.223 MUX Termination, defining number of ports, is not defined by this Recommendation. The use of a media field for the demultiplexed control stream (ITU-T H.245 messages in
41、 an ITU-T H.324 network) is optional. Its use depends on whether the ITU-T H.245 messages are “transported“ to specific termination(s) within the ITU-T H.248.1 Context, or if they are terminated at the MUX termination and then transported elsewhere using other mechanisms (e.g., as ITU-T H.248.1 Even
42、ts). If a media field for the control stream is used, the value of port MUST be zero (the LCN value for the ITU-T H.245 control channel). The value of proto is “H221“ or “H223“. The fmt value defines the payload type used to encode the specific media within the multiplexed ITU-T H.223 stream. If the
43、 media is “control“, the value of fmt is “H245“. 5.2 Binary encoding The Logical Channel Number is indicated through the use of Annex C/H.248.1 property “LCN“ C007. A value of 0 indicates that the stream is an ITU-T H.245 control stream. The multiplex value of “H221“ or “H223“ shall indicate that no
44、n-zero ITU-T H.245 LCN values are multiplexed ITU-T H.221 and ITU-T H.223 streams. 6 Example The following example describes a connection using the text encoding, where a multiplexed ITU-T H.223 stream, transported on a TDM bearer in a network using Annex C of ITU-T H.324 (“H.324M“), is demultiplexe
45、d in the MG. The demultiplexed media streams are then transported on an IP network using separate RTP connections for each media. The ITU-T H.248.1 Context includes three terminations; one TDM termination, one MUX termination and one RTP termination. Three ITU-T H.248 Streams are used in the example
46、: One for the multiplexed ITU-T H.223 stream (StreamID = 1), one for the demultiplexed audio stream (StreamID = 2) and one for the demultiplexed video stream (StreamID = 3). NOTE Only the SDP parameters affected by this Recommendation are included in the examples. 4 Rec. ITU-T H.248.20 (03/2013) 6.1
47、 Context model Figure 2 shows the Context model used in the example. NOTE ITU-T H.248.1 Stream 4 described in clause 6.4 is not shown in the picture since it is not associated with another termination in this example. It is used “internally“ within the MUX Termination. H.248.20_F02ContextMedia gatew
48、ayStream 1Stream 3Stream 2TermTDMTermMUXTermRTPFigure 2 Example context model 6.2 The media descriptor for the TDM termination TID= MyTDM/7/1 Media = Stream = 1 Local, Remote, and LocalControl Descriptors 6.3 The multiplex descriptor for the MUX termination Mux = H.223 MyTDM/7/1 6.4 The media descri
49、ptor for the MUX termination The payload type in the SDP m= lines defines the codec used for that specific stream received in the multiplexed TDM stream. Media = Stream = 1 LocalControl = H.324 properties etc , Stream = 2 ;demultiplexed audio stream Local = v=0 c=H223 - - m=audio 1 H223 4 ;codec G.723.1, LCN 1 , Remote = v=0 c=H223 - - m=audio 2 H223 4 ;codec G.723.1, LCN 2 , Stream = 3 ;demultiplexed video stream Rec. ITU-T H.248.20 (03/2013) 5 Loc
