1、 International Telecommunication Union ITU-T G.799.2TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (12/2009) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital terminal equipments Other terminal equipment Mechanism for dynamic coordination of signal processing functions
2、Recommendation ITU-T G.799.2 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF IN
3、TERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDIA A
4、ND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 General G.700G.709 Coding of voice and audio signals G.710G.729 Principal characteristics of primary multiplex equipment G.730G.739 Principal characteristics of second order multiplex equipment G.740G.749 Principal
5、characteristics of higher order multiplex equipment G.750G.759 Principal characteristics of transcoder and digital multiplication equipment G.760G.769 Operations, administration and maintenance features of transmission equipment G.770G.779 Principal characteristics of multiplexing equipment for the
6、synchronous digital hierarchy G.780G.789 Other terminal equipment G.790G.799DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA
7、 OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.799.2 (12/2009) i Recommendation ITU-T G.799.2 Mechanism for dynamic coordination of signal proces
8、sing functions Summary As a result of the evolution of the telecommunication networks in recent years, signal processing features such as voice quality enhancement processing may now be found in different communication nodes and combined in different ways on a bearer path. However, instead of the in
9、tended purpose of preserving or enhancing voice quality, signal processing functions deployed on the same bearer path could cause overall voice quality degradation due to undesirable side-effects of the interaction of the individual functions. The concerns about the interaction of signal processing
10、functions can be mitigated if the communication nodes are properly coordinated and controlled to provide the end-to-end communication with the optimal placement of signal processing functions. Whilst local operators may have direct control of some of the equipment, this control by the local operator
11、s may not extend to all the nodes in call scenarios such as inter-system links. The traditional “static“ approach to the coordination of signal processing functions, such as those found in voice enhancement equipment, may not meet the requirements of modern call topologies, which tend to be dynamic.
12、 Lack of coordination of the signal processing functions may result in voice quality degradation. Recommendation ITU-T G.799.2 defines a generic framework for a coordination mechanism intended to minimize undesirable interactions of signal processing functions present on bearer paths of a communicat
13、ion link. The goal of this Recommendation is to provide a mechanism that can be used to optimize the end-to-end voice quality. History Edition Recommendation Approval Study Group 1.0 ITU-T G.799.2 2009-12-14 16 ii Rec. ITU-T G.799.2 (12/2009) FOREWORD The International Telecommunication Union (ITU)
14、is the United Nations specialized agency in the field of 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 issuin
15、g 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 Recommendations on these topic
16、s. 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 Recommendation, the expression “
17、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., interoperability or applicability) an
18、d 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 compliance with the Recommend
19、ation 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, validity or applicability of cla
20、imed 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 received notice of intellectual property, protected by patents, which may be required to implement this Recommend
21、ation. 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/. ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, wit
22、hout the prior written permission of ITU. Rec. ITU-T G.799.2 (12/2009) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 3 4 Abbreviations and acronyms 4 5 Dynamic coordination mechanism . 5 5.1 Levels of support 5 5.
23、2 Functions 5 5.3 Methodology . 5 5.4 Information to be exchanged 9 5.5 Enabling/disabling SPFs . 9 6 Coordination rules 10 Annex A Format and structure for capability list implementation . 12 Appendix I Network scenario examples for operating dynamic coordination mechanism among SPEs 14 I.1 Packet
24、network to packet network 14 I.2 Circuit-switched network to circuit-switched network 17 I.3 Packet network to circuit-switched network 19 Bibliography. 24 Rec. ITU-T G.799.2 (12/2009) 1 Recommendation ITU-T G.799.2 Mechanism for dynamic coordination of signal processing functions 1 Scope This Recom
25、mendation applies to signal processing functions that are intended for use in a communication link between terminal devices through network connections. Examples of signal processing functions are echo cancellers, acoustic echo control, automatic level control and noise reduction. Communication netw
26、orks include GSTN, IP networks, wireless mobile networks and any combination of them. This Recommendation defines a generic framework for a coordination mechanism intended to minimize undesirable interactions of signal processing functions present on bearer paths of a communication link. The goal of
27、 this Recommendation is to provide a mechanism that can be used to optimize the end-to-end voice quality. The signal processing functions subject to coordination by using this Recommendation could be present in the terminal devices and/or the communication networks. The mechanism performing dynamic
28、coordination of signal processing functions includes the following components: capability announcement, capability identification, capability interaction resolution and capability change. This Recommendation does not define the protocol to implement the coordination mechanism, but rather defines all
29、 the elements and information to be exchanged in support of the coordination mechanism. The implementation aspects of this mechanism will be defined in other ITU-T Recommendations. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in th
30、is 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; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edi
31、tion 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 Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.160 Recommendation IT
32、U-T G.160 (2008), Voice enhancement devices. ITU-T G.161 Recommendation ITU-T G.161 (2004), Interaction aspects of signal processing network equipment. ITU-T G.168 Recommendation ITU-T G.168 (2009), Digital network echo cancellers. ITU-T G.169 Recommendation ITU-T G.169 (1999), Automatic level contr
33、ol devices. ITU-T G.799.1 Recommendation ITU-T G.799.1 (2004), Functionality and interface specifications for GSTN transport network equipment for interconnecting GSTN and IP networks. 2 Rec. ITU-T G.799.2 (12/2009) 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following ter
34、ms defined elsewhere: 3.1.1 acoustic echo ITU-T G.160: Acoustic echo is the reflected signal resulting from the acoustic path between the earphone/loudspeaker and microphone of a terminal, hand-held or hands-free mobile station. 3.1.2 automatic level control device ITU-T G.161: An automatic level co
35、ntrol device (ALC) is a signal processing function located in the digital transmission path which automatically adjusts the level of a signal towards a predetermined value. Devices which modify the frequency response or spectral content of the signal in such a way as to affect the overall level of t
36、he signal are also defined as ALC devices for the purpose of this Recommendation. An ALC device is designed to process signals in one direction of transmission (see Figure 1). G.799.2(09)_F01Receive, or non-processing, pathALC deviceReceive in Receive outALCprocessingSend, or processing, pathSend ou
37、t Send inRinRoutSoutSinFigure 1 Block diagram of an automatic level control device ITU-T G.169 3.1.3 cancelled end ITU-T G.161: The side of an echo canceller which contains the echo path on which this echo canceller is intended to operate. This includes all transmission facilities and equipment (inc
38、luding the hybrid and terminating telephone set) which is included in the echo path. 3.1.4 network acoustic echo controller ITU-T G.161: Network acoustic echo controllers are devices placed in the 4-wire portion of a circuit and used for reducing cancelled-end acoustic echo. 3.1.5 network echo cance
39、ller ITU-T G.161: An network echo canceller is a voice-operated device placed in the 4-wire portion of a circuit and used for reducing the cancelled-end echo present on the send path by subtracting an estimation of that echo from the cancelled-end echo (see Figure 2). Rec. ITU-T G.799.2 (12/2009) 3
40、G.799.2(09)_F02HybridNetworkelementsNetworkelementsSinAECHOCancelled endRoutReceive pathEcho estimator and othercontrol circuitryDigital subtractorACANCSend pathNon-linearprocessorANLPLRESSoutLRETNon-cancelledendLRinRinFigure 2 Block diagram of an echo canceller ITU-T G.168 3.1.6 network echo suppre
41、ssors ITU-T G.161: A network echo suppressor is a voice-operated device placed in the 4-wire portion of a circuit and used for inserting loss in the transmission path to suppress echo. The path in which the device operates may be an individual circuit path or a path carrying a multiplexed signal. 3.
42、1.7 terminal acoustic echo controller ITU-T G.161: Terminal acoustic echo controllers are voice-operated devices installed in audio terminals on the customer premises, used for the purpose of eliminating acoustic echoes and protecting the communication from howling due to acoustic feedback from loud
43、speaker to microphone. 3.1.8 voice enhancement device ITU-T G.161: Voice enhancement devices are intended for use in digital network-based equipment for mobile applications. Voice enhancement functions include the control of acoustic echo generated by wireless handsets, noise reduction, and the reco
44、gnition and accommodation of tandem free operation (TFO) and interworking function (IWF) signals. 3.1.9 voice gateways ITU-T G.161: A voice gateway is a subset of a gateway that deals with voice and voiceband traffic only, and not data or video traffic. 3.2 Terms defined in this Recommendation This
45、Recommendation defines the following terms: 3.2.1 automatic listener enhancement (ALE) device: An automatic listener enhancement (ALE) device is defined as any signal processing function located in the digital transmission path that adjusts the level of a signal in one transmission direction based o
46、n the measurements of signal in the other transmission direction with the purpose of enhancing audibility in high environmental noise conditions. Devices that modify the frequency response or spectral content of the signal in such a way as to affect the overall level of the signal are also defined a
47、s ALE devices. NOTE The performance requirement for this function is outside the scope of this Recommendation. 3.2.2 signal processing equipment (SPE): A stand-alone physical entity that supports one or more signal processing functions. Examples of signal processing equipment are signal processing n
48、etwork equipment (SPNE) ITU-T G.161 and signal processing terminal devices. 3.2.3 signal processing function: A software component or a hardware entity that performs voice processing such as, but not limited to, electric or acoustic echo control, noise reduction or automatic level control. 4 Rec. IT
49、U-T G.799.2 (12/2009) 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AEC Acoustic Echo Control ACM Address Complete Message ALC Automatic Level Control ALE Automatic Listener Enhancement ANM Answer Message BSC Base Station Controller CNG Comfort Noise Generation EC Echo Canceller ECD Echo Control Device GSTN General Switched Telephone Network IAM Initial Address Message IP Internet Protocol IWF Interworking Function LSB Least Significant Bit MGW Media Gatew
