ITU-T M 660-1988 Periodical in-station tests of echo suppressors complying with Recommendations G 161 and G 164《符合建议G 161和G 164的回波抑制器的定期站内测试》.pdf
《ITU-T M 660-1988 Periodical in-station tests of echo suppressors complying with Recommendations G 161 and G 164《符合建议G 161和G 164的回波抑制器的定期站内测试》.pdf》由会员分享,可在线阅读,更多相关《ITU-T M 660-1988 Periodical in-station tests of echo suppressors complying with Recommendations G 161 and G 164《符合建议G 161和G 164的回波抑制器的定期站内测试》.pdf(6页珍藏版)》请在麦多课文档分享上搜索。
1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G04%,%0(/.%G0G0#)2#5)430%2)/$)#!,G0G0).G1334!4)/.G0G04%343G0G0/&G0G0%#(/35002%33/23G0G0#/-0,9).G0G07)4(2%#/-%.$!4)/.3G0G0 G0G0!.$G0G0 )45G134G0G02ECOMMENDATIONG0G0- (Extract from th
2、e “LUEG0“OOK)NOTES1 ITU-T Recommendation M.660 was published in Fascicle IV.1 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book vers
3、ion and copyright conditions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be repr
4、oduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.1 Rec. M. 660 1Recommendation M.660Fascicle IV.1 Rec. M. 660PERIODICAL IN-STATION TESTS OF ECHO SUPPRESSORS COMPLYINGWITH RECOMMENDATI
5、ONS G.161 AND G.164Note 1 Certain of the tests in this Recommendation may conveniently be carried out on an in-station (or in-circuit) basis using measuring equipment to the specification in Recommendation O.25 1. This equipment will notprovide reliable test results for a circuit which is routed thr
6、ough circuit multiplication systems (CMS) employinginterpolation techniques this includes the case where a circuit is routed over time division multiple access/digital speechinterpolation (TDMA/DSI) satellite channels and therefore should not be used in this instance unless a permanent trunk-channel
7、 association in both directions of transmission can be made for the duration of the test sequence. The reason forthis is that without such a trunk-channel association, circuit continuity may not be maintained within the CMS in theabsence of a signal and during very low signal level conditions.Note 2
8、 The tests and periodicities specified in this Recommendation have been prepared to meet the needs ofecho suppressors conforming to Recommendations G.161 2 and G.164 3.1 Tests and periodicities applied to valve, rectifier and relay type echo suppressors1.1 The following tests should be made monthly:
9、1.1.1 Check of suppression operate levelIf not within 2 dB of the initial value, readjust to be as close to the initial value as possible.1.1.2 Check of suppression loss (blocking attenuation)The suppression loss should not be less than 30 dB in the frequency range 200 - 3500 Hz and not lessthan 40
10、dB in the range 1000 - 1500 Hz.1.1.3 Check of differential sensitivitya) Check that the suppression loss is removed in the presence of signal on the send path of sufficientmagnitude as compared with a signal on the receive path. This check should be made with magnitudes ofthe signal on the receive p
11、ath, ranging from the operate level to the expected maximum speech level.b) Check also that the suppression loss is not removed by the echo produced under the conditionscorresponding to the worst expected return loss. Use of an interrupted signal at the operate-frequency or atest speech signal is li
12、kely to be effective for this check.Note These tests will be necessary when the break-in function is provided.1.1.4 Check of disabling facilitiesa) Some echo suppressors can be disabled by the associated signalling and switching equipment. The correctperformance of this function, when provided, shou
13、ld be checked.b) Some echo suppressors can be disabled by special audio frequency signals on the circuit. The correctperformance of this function, when provided, should be checked.1.2 The following characteristic times should be measured every six months and if they are not within 20% of theinitial
14、values they should be readjusted to be as close to the initial values as possible.1.2.1 Suppression operate timesa) Relay-type echo suppressor. The operate time should not exceed 4 ms. Alternatively, the operate timeshould not be greater than 12 ms with a test signal at the operating frequency and 3
15、 dB above the operatelevel.b) Valve or rectifier type echo suppressor. The operate time should not exceed 4 ms. The period subsequentto the operate time, during which the specified suppression loss is achieved, should not exceed 0.5 ms.Thereafter, as long as the test signal is applied, the loss shou
16、ld not fall below that specified.2 Fascicle IV.1 Rec. M. 6601.2.2 Suppression hangover timeThe hangover time of the echo suppressor should be 50 ms. Exceptionally, where there is a long chain ofnational or international circuits beyond the point where the half-echo suppressor is fitted, the hangover
17、 time should be70 ms.2 Tests and periodicities applicable to semi-conductor type echo suppressors2.1 The following tests should be made every six months:2.1.1 Check of suppression operate levelIf not within 2 dB of 31 dBm0 readjust to be as close to this level as possible.2.1.2 Check of suppression
18、lossThe suppression loss should be at least 50 dB.2.1.3 Check of break-in differential sensitivity and receive lossCheck that the suppression loss is removed when the signal applied to the send-in port is within 2 dB of thelevel of a signal of the same frequency applied to the receive-in port. The l
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