1、 International Telecommunication Union ITU-T J.161TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2007) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS IPCablecom Audio and video codec requirements and usage for the provision of bidirectional
2、 audio services over cable television networks using cable modems ITU-T Recommendation J.161 ITU-T Rec. J.161 (06/2007) i ITU-T Recommendation J.161 Audio and video codec requirements and usage for the provision of bidirectional audio services over cable television networks using cable modems Summar
3、y ITU-T Recommendation J.161 specifies the media aspects of the interfaces between IPCablecom client devices for audio and video communication. Specifically, it identifies the audio and video codecs necessary to provide the highest quality and the most resource-efficient service delivery to the cust
4、omer. This Recommendation also specifies the performance required in client devices to support future IPCablecom codecs. Additionally, this Recommendation describes a suggested methodology for optimal network support for codecs. Source ITU-T Recommendation J.161 was approved on 20 June 2007 by ITU-T
5、 Study Group 9 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. J.161 (06/2007) 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 p
6、ermanent 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 Assembly (WTSA), which meets every four years, esta
7、blishes 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 fall within ITU-Ts purview, the necessary st
8、andards 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 this Recommendation is voluntary. However, the R
9、ecommendation 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 language such as “must“ and the negative equivalents
10、 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 Recommendation may involve the use of a claimed
11、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 approval of this Recommendation, ITU had recei
12、ved 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 patent database at http:/www.itu.int/ITU-T/ipr
13、/. ITU 2008 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. J.161 (06/2007) iii CONTENTS Page 1 Scope 1 1.1 Introduction and overview 1 1.2 Purpose of this Recommendation. 1 1.3 Phasing of requiremen
14、ts . 1 2 References. 2 2.1 Normative references 2 2.2 Informative references 3 3 Terms and definitions . 4 4 Abbreviations, acronyms and conventions. 5 4.1 Abbreviations and acronyms 5 4.2 Conventions 6 5 Background. 6 5.1 IPCablecom voice communications quality requirements . 7 5.2 Network preparat
15、ion for codec support 7 6 Device requirements for audio codec support 9 6.1 Dynamic update capability. 10 6.2 Maximum service outage . 10 6.3 Minimum processing capability . 10 6.4 Minimum audio codec storage capability. 11 7 Audio codecs specifications . 11 7.1 Feature support . 11 7.2 Mandatory co
16、dec 16 7.3 Recommended codecs 17 7.4 Optional features 17 7.5 Session description of codecs. 18 8 Video requirements. 22 8.1 Overview 22 8.2 IPCablecom video devices . 22 8.3 Video encoder requirements. 23 8.4 Video format requirements. 23 8.5 H.263 annexes 24 8.6 Multipoint conferencing support 27
17、8.7 Signalling messages 28 9 RTP and RTCP usage . 29 9.1 RTP requirements. 29 9.2 RTCP requirements 29 Appendix I Codec comparison tables . 37 ITU-T Rec. J.161 (06/2007) 1 ITU-T Recommendation J.161 Audio and video codec requirements and usage for the provision of bidirectional audio services over c
18、able television networks using cable modems 1 Scope This Recommendation specifies the media aspects of the interfaces between IPCablecom client devices for audio and video communication. Specifically, it identifies the audio and video codecs necessary to provide the highest quality and the most reso
19、urce-efficient service delivery to the customer. This Recommendation also specifies the performance required in client devices to support future IPCablecom codecs. Additionally, this Recommendation describes a suggested methodology for optimal network support for codecs. 1.1 Introduction and overvie
20、w The quality of audio and video delivered over the IPCablecom architecture will depend on multiple factors: the end device performance, the networks inherent quality, and the intelligence of the system resource allocation policy. This Recommendation specifies codecs and capabilities supporting audi
21、o and video applications, with a particular emphasis on the stringent requirements of IP-based voice communications. Acceptable voice communications functionality imposes strict delay and packet-loss criteria on IP implementations and will thus stress system resources, particularly if bandwidth beco
22、mes congested or saturated. Video applications while more forgiving to dropped packets and delay require bandwidth of at least an order of magnitude more than audio applications. The IPCablecom architecture is designed to support both voice and video applications simultaneously. Speech and video com
23、pression are evolving technologies. New algorithms are being enabled as more sophisticated and higher performing processors become available at lower cost. Additionally, the system infrastructure and mechanisms for allocating resources will evolve. Due to this dynamism, the priority in designing the
24、 architecture is to define a robust system to accommodate evolving technology without creating a legacy burden. Therefore, the IPCablecom philosophy is to establish cost-effective envelopes for network and device performance to enable the most appropriate current technology, while allowing upgrades
25、as technology and market needs evolve. To address near-term market needs, this Recommendation also specifies codec and performance mandates to deliver the quality-of-service necessary for launching competitive services. 1.2 Purpose of this Recommendation The purpose of this Recommendation is to exte
26、nd the existing IPCablecom v1Codec Recommendation by introducing two new low-bit codecs, ITU-T T.38 fax relay for reliable fax transmission, IETF RFC 2833 DTMF Relay for reliable DTMF transmission and metrics to measure voice quality. It is issued to facilitate design and field-testing leading to th
27、e manufacturability and interoperability of conforming hardware and software by multiple vendors. 1.3 Phasing of requirements The codec requirements contained in this Recommendation cover both audio and video multimedia terminals (MTAs) and trunking gateways (media gateway). The term MTA-2 is used t
28、o define a terminal supporting video. 2 ITU-T Rec. J.161 (06/2007) In the initial phase of IPCablecom, MTAs are not required to support the MTA-2 requirements as defined in clause 8. MTAs MUST support the requirements for audio terminals as defined in clauses 5, 6, 7, and 9. Support for video termin
29、als will be REQUIRED in later phases of IPCablecom. All MTA-2s MUST support the requirements defined in clause 8. 2 References 2.1 Normative references The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Rec
30、ommendation. 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 Recommendations and other refe
31、rences 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 G.107 ITU-T Recommendation G.107 (2005), The E-model, a computati
32、onal model for use in transmission planning. ITU-T G.165 ITU-T Recommendation G.165 (1993), Echo cancellers. ITU-T G.168 ITU-T Recommendation G.168 (2007), Digital network echo cancellers. ITU-T G.711 ITU-T Recommendation G.711 (1988), Pulse code modulation (PCM) of voice frequencies. ITU-T G.728 IT
33、U-T Recommendation G.728 (1992), Coding of speech at 16 kbit/s using low-delay code excited linear prediction. ITU-T G.729 ITU-T Recommendation G.729 (2007), Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-exited linear prediction (CS-ACELP). ITU-T J.170 ITU-T Recommendation J.
34、170 (2005), IPCablecom security specification. ITU-T J.171.x ITU-T Recommendation J.171.x (2005), IPCablecom trunking gateway control protocol (TGCP). ITU-T P.56 ITU-T Recommendation P.56 (1993), Objective measurement of active speech level. ITU-T P.561 ITU-T Recommendation P.561 (2002), In-service
35、non-intrusive measurement device Voice service measurements. ITU-T T.38 ITU-T Recommendation T.38 (2007), Procedures for real-time Group 3 facsimile communication over IP networks. ITU-T V.18 ITU-T Recommendation V.18 (2000), Operational and interworking requirements for DCEs operating in the text t
36、elephone mode. IETF RFC 2833 IETF RFC 2833 (2000), RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals. IETF RFC 3611 IETF RFC 3611 (2003), RTP Control Protocol Extended Reports (RTCP XR). IETF RFC 3550 IETF RFC 3550 (2003), RTP: A Transport Protocol for Real-Time Applications. ITU-T
37、Rec. J.161 (06/2007) 3 IETF RFC 3551 IETF RFC 3551 (2003), RTP Profile for Audio and Video Conferences with Minimal Control. IETF RFC 3951 IETF RFC 3951 (2004), Internet Low Bit Rate Codec (iLBC). IETF RFC 3952 IETF RFC 3952 (2004), Real-time Transport Protocol (RTP) Payload Format for internet Low
38、Bit Rate Codec (iLBC) Speech. IETF RFC 4298 IETF RFC 4298 (2005), RTP Payload Format for BroadVoice Speech codecs. ANSI T1.521 ANSI T1.521-1999, Packet Loss Concealment for Use with ITU-T Recommendation G.711. IMTC IMTC Voice-Over-IP Forum Service Interoperability Implementation Agreement 1.0, dated
39、 December 1, 1997. ANSI/SCTE 24-21 ANSI/SCTE 24-21 (2006), BV16 Speech Codec Specification for Voice over IP Applications in Cable Telephony. 2.2 Informative references ITU-T F.703 ITU-T Recommendation F.703 (2000), Multimedia conversational services. ITU-T H.243 ITU-T Recommendation H.243 (2005), P
40、rocedures for establishing communication between three or more audiovisual terminals using digital channels up to 1920 kbit/s. ITU-T H.245 ITU-T Recommendation H.245 (2006), Control protocol for multimedia communication. ITU-T H.261 ITU-T Recommendation H.261 (1993), Video codec for audiovisual serv
41、ices at p 64 kbit/s. ITU-T H.263 ITU-T Recommendation H.263 (2005), Video coding for low bit rate communication. ITU-T H.323 ITU-T Recommendation H.323 (2006), Packet-based multimedia communications systems. ITU-T H.324 ITU-T Recommendation H.324 (2005), Terminal for low bit-rate multimedia communic
42、ation. ITU-T J.160 ITU-T Recommendation J.160 (2005), Architectural framework for the delivery of time-critical services over cable television networks using cable modems. ITU-T J.163 ITU-T Recommendation J.163 (2005), Dynamic quality of service for the provision of real-time services over cable tel
43、evision networks using cable modems. ITU-T P.862 ITU-T Recommendation P.862 (2001), Perceptual evaluation of speech quality (PESQ): An objective method for end-to-end speech quality assessment of narrow-band telephone networks and speech codecs. ITU-T T.140 ITU-T Recommendation T.140 (1998), Protoco
44、l for multimedia application text conversation. IETF RFC 2327 IETF RFC 2327 (1998), SDP: Session Description Protocol. IETF RFC 4103 IETF RFC 4103 (2005), RTP Payload for Text Conversation. COX COX (R.V.): Current Methods of Speech Coding, International Journal of High Speed Electronics another vend
45、or may omit the same item. 5 Background This clause outlines the IPCablecom architecture support elements and the DOCSIS network infrastructure necessary to deliver quality audio and video service. It is intended to clarify external interfaces and functional requirements necessary to implement the t
46、argeted audio and video quality using speech and video codecs. ITU-T Rec. J.161 (06/2007) 7 The key requirement for voice communications using IP transmission is the ability to attain “toll“ or better audio quality. Given the variable nature of shared packet mediums and the stringent human-factor re
47、quirements of this quality standard, it is necessary to optimize multiple system parameters to attain this goal. Additionally, IPCablecom has been tasked with offering superior quality, exceeding current PSTN standards where feasible. Key requirements from the IPCablecom product definition requiring
48、 architectural optimization for codecs follow. 5.1 IPCablecom voice communications quality requirements As defined in the IPCablecom architecture Recommendation ITU-T J.160, requirements for toll-quality voice communications service in IPCablecom include numerous metrics to ensure competitive or sup
49、erior quality and service to the PSTN. In order to support these requirements, network plant and equipment may have to be groomed. In order to provide guidelines for that grooming, several network implications affecting codec performance are discussed below. 5.2 Network preparation for codec support The critical areas of network performance, which must be optimized in tandem with codecs, are packet loss, delay and jitter. Elaboration of network/codec implications for each of these areas follows. 5.2.1
