1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STAN DARD IZAT ION SECT0 R OF ITU G.169 (06i99) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS International telephone connections and circuits - Apparatus associated with long-distance telephone circuits Automatic
2、 level control devices ITU-T Recommendation G. 169 (Previously CCITT Recommendation) ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS - INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G. 1 OO-G. 199 G. I 004.1 O9 G. I I O-G. 1 1 9 General definitions Gener
3、al Recommendations on the transmission quality for an entire international General characteristics of national systems forming pari of international connections telephone connection General characteristics of the 4-wire chain formed by the international circuits and national extension circuits Gener
4、al characteristics of the 4-wire chain of international circuits; international transit circuits G .I 20-G . I 29 G.130-G.139 G.140-G.149 General characteristics of international telephone circuits and national extension G. 1 50-G. I 59 Transmission plan aspects of special circuits and connections u
5、sing the international telephone connection network Protection and restoration of transmission systems Software tools for transmission systems INTERNATIONAL ANALOGUE CARRIER SYSTEM GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER- TRANSMISSION SYSTEMS INDIVIDUAL CHARACTERISTICS OF INTERNATIONA
6、L CARRIER TELEPHONE SYSTEMS ON METALLIC LINES GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE METALLIC LINES SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY TES TING EQUIPMEN TS TRANSMISSION MEDIA CHARACTERISTICS DIGITAL
7、 TRANSMISSION SYSTEMS TERMINAL EQUIPMENTS DIGITAL NETWORKS DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.170-G.179 G.180-G.189 G. 19043.199 G.200-G.299 G .300-G. 399 G.400-G .449 G.450-G.499 G .700-G. 799 G.800-G.899 G.900-G.999 For further details, please refer to ITU-T List of Recommendations. STD.1T
8、U-T RECNN GmLbS-ENGL 1999 48b2591 Ob64772 T7B W ITU-T RECOMMENDATION G.169 AUTOMATIC LEVEL CONTROL DEVICES Summary This Recommendation applies to testing of Automatic Level Control (ALC) devices intended for use in digital network-based equipment. It does not apply to subscriber-based level control
9、devices, devices that operate in the analogue domain, or any means of fixed level control within the network which may be part of an overall network transmission plan. The scope of this Recommendation is to define certain performance constraints for network ALC devices and, where appropriate, to def
10、ine laboratory tests that may be performed on an ALC device to verify that these constraints are met. An ALC device that satisfies all the constraints and passes all of the tests in this Recommendation should ensure (but will not guarantee) that the pre-existing standard of overall network performan
11、ce (e.g. the transmission of speech, voiceband data and other voiceband signals, ISDN, etc.) is not degraded when the ALC device is installed in the network. This Recommendation also describes the general characteristics of ALC devices and indicates what characteristics are important to provide acce
12、ptable performance in the network. Issues relating to the interaction of ALC devices with other network and subscriber equipment are also discussed in this Recommendation. This Recommendation does not define a standard algorithm. This Recommendation does not define planning rules, deployment aspects
13、 or target levels for ALC devices. Source ITU-T Recommendation G.169 was prepared by ITU-T Study Group 15 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 22nd of June 1999. Recommendation G.169 (06/99) 1 STD-ITU-T RECMN GeLbq-ENGL 1999 FOREWORD ITU (International Telec
14、ommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on th
15、em with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval
16、 of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation the te
17、rm recognized operating agency (ROA) includes any individual, company, corporation or governmental organization that operates a public correspondence service. The terms Administration, ROA and public correspondence are defined in the Constitution of the ITU (Geneva, 1992). INTELLECTUAL PROPERTY RIGH
18、TS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserte
19、d by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned
20、 that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 1999 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfi
21、lm, without permission in writing from the ITU. 11 Recommendation G.169 (06/99) 1 2 3 4 5 5.1 5.2 5.3 5.4 6 6.1 6.2 6.3 7 7.1 7.2 7.3 7.4 7.5 STD ITU-T RECMN CONTENTS 48b2571 Obb4774 840 Page Scope References Terms and definitions . Abbreviations and acronyms Characteristics of ALC devices General .
22、 ALC characteristics Tandemed operation . Delay performance . Test signals . Test signal for level and gain checks Electrical circuit noise Environmental noise . Tests . Stability 7.1.1 7.1.2 Networks with echo control Echo Noise tolerance . Signalling tones 7.4.1 DTMF tests . Voiceband data and fac
23、simile transmission . 7.5.1 Disabler characteristics . 7.5.2 an ALC device is not disabled by 2 1 O0 Hz . Networks without pre-existing echo control . Tests to confirm satisfactory voiceband data and fax performance when Annex A . Guidance for measuring signal levels in networks . their placement in
24、 the PSTN Appendix I . Guidance for the design of Automatic Level Control (ALC) algorithms and I . 1 Introduction 1.2 Discussion 1.3 ALC considerations Recommendation G.169 (06/99) 1 i 2 3 4 4 4 5 5 5 6 6 7 7 10 12 12 15 15 17 19 20 20 20 21 . 111 Page 1.3.1 Location of ALC . 21 1.3.2 Algorithmic an
25、d subjective considerations . 22 1.3.3 Equipment issues . 23 1.3.4 Echo 23 23 1.3.5 Loop stability . Appendix II - Considerations relating to ALC deployment 11.2 Tandemed operation . 25 24 II. 1 Location of ALC . 24 iv Recommendation G.169 (06/99) Recommendation G.169 AUTOMATIC LEVEL CONTROL DEVICES
26、 (Geneva, 1999) 1 Scope This Recommendation applies to testing of Automatic Level Control (ALC) devices intended for use in digital network-based equipment. An ALC device is defined as any signal processing function located in the digital transmission path which automatically adjusts the level of a
27、signal towards a predetermined value. Devices which modifj 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 as ALC devices for the purpose of this Recommendation. This Recommendation does not apply to subscriber-base
28、d level control devices, devices that operate, in the analogue domain, or any means of fixed level control within the network which may be part of an overall network transmission plan. The scope of this Recommendation is to define certain performance constraints for network ALC devices and, where ap
29、propriate, to define laboratory tests that may be performed on an ALC device to veri that these constraints are met. An ALC device that satisfies all the constraints and passes all of the tests in this Recommendation should ensure (but will not guarantee) that the pre-existing standard of overall ne
30、twork performance (e.g. the transmission of speech, voiceband data and other voiceband signals, ISDN, etc.) is not degraded when the ALC device is installed in the network. This Recommendation also describes the general characteristics of ALC devices and indicates what characteristics are important
31、to provide acceptable performance in the network. Issues relating to the interaction of ALC devices with other network and subscriber equipment are also discussed in this Recommendation. This Recommendation does not define a standard algorithm. This Recommendation does not define planning rules, dep
32、loyment aspects, or target levels for ALC devices. This information may be found in Recommendations currently under development in ITU-T Study Group 12. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisio
33、ns of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendati
34、ons and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. i ITU-T Recommendation P.56 (1 993), Objective measurement of active speech level. 2 ITU-T Recommendation G. 122 (1 993), Influence of national systems on stability and talker echo in i
35、nternational connections. 3 CCITT Recommendation G. 164 (1 988), Echo suppressors. 4 ITU-T Recommendation G. 165 (1 993), Echo Cancellers. Recommendation G.169 (06/99) 1 ITU-T Recommendation V.8 (1 998), Procedures for starting sessions of data transmission over the public switched telephone network
36、 ITU-T Recommendation V.25 (1 996), Automatic answering equipment and general procedures for automatic culling equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls. ITU-T Recommendation T
37、30 (1 996), Procedures for document facsimile transmission in the general switched telephone network. ITU-T Recommendation T.4 (1 996), Standardization of Group 3 Facsimile terminals for document transmission. ITU-T Recommendation G.168 (1997), Digital network echo cancellers. ITU-T Recommendation
38、P.56 1 (1 996), In-service non-intrusive measurement device - Voice service measurements. ITU-T Recommendation P.501 (1996), Test signalsfor use in Telephonometry. CCITT Recommendation 4.24 (1 988), Multifrequency push-button signal reception. Terms and definitions This Recommendation defines the fo
39、llowing terms: 3.1 ALC device: 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 l
40、evel of the 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. Receive or non-processing path ALC Device r - - - - - - - - - - 1 Receive out Receive in Ri“ I 7 R0“t I I I I I I I
41、I I I I I I I I I I I I I I I Send out I Send in Si“ sou 4 I 1- - - - - - - - - - - 4 T1530230-98 Send or processing path Figure VG.169 - Block diagram of an ALC device 3.2 Disabled ALC device: An ALC device that has been forced into a 64 kbit/s bit-sequence integrity mode of operation, by whatever
42、means. 3.3 Echo canceller: A device placed in the 4-wire portion of a circuit and used for reducing cancelled-end echo present on the send path by subtracting an estimation of that echo from the cancelled-end echo. 2 Recommendation 6.169 (06/99) 3.4 Full ALC device: An ALC device designed to process
43、 signals in both directions of transmission. 3.5 Full echo canceller: An echo canceller designed to cancel echoes in both directions (Le. near-end and far-end echoes). 3.6 Laboratory tests: Tests which may be performed in a laboratory or any environment where the ALC device is not installed in the n
44、etwork and is therefore not in service. 3.7 Target level: For a particular signal type, the input signal level for which an active (enabled) ALC device will progress to unity gain. At other input signal levels, the output level of the ALC device will be adjusted towards the target level. Note that w
45、ith some ALC devices, the target level may be different for different types of signals, e.g. the target level for speech may be different from the target level for a tone. Also, the treatment of signals which are above the target level may be different from the treatment of signals which are below t
46、he target level. In principle, an advanced ALC device may feature more than one target level, depending on the transmitted signal (e.g. speech, data, or DTMF tones). 4 Abbreviations and acronyms This Recommendation uses the following abbreviations: ALC Automatic level control AID Analogue-to-digital
47、 converter css Composite source signal DIA Digital-to-analogue converter DCME Digital circuit multiplication equipment DTMF Dual-tone multi-frequency ERL Echo return loss ISDN Integrated services digital network 5 Characteristics of ALC devices 5.1 General This Recommendation is applicable to Automa
48、tic Level Control (ALC) devices installed in digital network-based equipment. An ALC device is defined as any signal processing function located in the digital transmission path which automatically adjusts the level of a signal towards a predetermined value. Devices which modi the frequency response
49、 or spectral content of the signal in such a way as to affect the overall level of the signal are also defined as ALC devices for the purpose of this Recommendat ion. 5.2 ALC characteristics ALC devices installed in the network should have the following characteristics: 1) 2) 3) The ability to introduce restricted gain or loss in the circuit to maintain the level of a call at a predetermined value. The ability to maintain the stability of a connection at all times (both during call set-up and for the duration of the call), in cases with and without associated echo
