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
19、evel of the signal applied at the receive-in portshould be between 15 and 20 dBm0. Check that the loss in the receive path (receive loss), when break-in occurs isbetween 5 and 15 dB when the level applied at the receive-in port is in the range 15 to 20 dBm0.2.1.4 Check of signalling disablingThe ope
20、ration and release of the signalling disabler circuit should be checked.2.1.5 Check of tone disablingThe characteristics of the tone disabler circuit should be checked and should be within the following limits:a) Disabler sensitivityThe disabler should operate for any single frequency within the dis
21、abling design range at a level of 30 dBm0.The disabler should be released when the disabling tone is reduced to a level of 36 dBm0.b) Guard sensitivityWith either a 1020 Hz signal applied to the receive-in port and a 2100 Hz signal at a level of 28 dBm0applied simultaneously to the send-in port, the
22、 suppressor should disable when the level of the 1020 Hzsignal is below 33 dBm0 and should not disable when this signal is above 28 dBm0.c) Broadband holding and releaseOnce disabled a 31 dBm0 signal of either 1020 Hz should hold disabling and a 36 dBm0 signal shouldnot.2.2 The following characteris
23、tic times should be measured every six months and should be within the limitsshown:2.2.1 Suppressiona) Suppression operate time: 5 ms (maximum).b) Suppression hangover time: 40-75 ms.2.2.2 Break-ina) Break-in operate time: 30 ms (maximum).b) Break-in hangover time: 150-350 ms.2.2.3 Tone disabilitya)
24、 Tone disabler operate time: 300 100 ms.b) Tone disabler hangover time: 250 150 ms.Note The disabler should not release for breaks of less than 100 ms in the disabling tone.Fascicle IV.1 Rec. M. 660 3(For definitions of terms see Recommendation G.161 2.)3 Tests and periodicities applicable to echo s
25、uppressors conforming to Recommendation G.1643.1 The following tests should be made, e.g. every six months.Note 1 If the echo suppressor interface is digital (for example, 2048 kbit/s) the levels prescribed for thevarious tests are coded in corresponding bit sequences.Note 2 Modern digital technique
26、s may allow the tests listed below to be carried out continuously withoutcausing any disturbance of the traffic on the circuit (in-built test system).3.1.1 Check of suppression operate levelThe operate level in the receive paths should be within 2 dB of 31 dBm0.3.1.2 Check of suppression lossThe sup
27、pression loss should be at least 50 dB.3.1.3 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 the range 0 to3 dB of the level of a signal of the same frequency applied to the receive-in port. T
28、he level of the signal applied at thereceive-in port should be any single value within the range 15 and 20 dBm0.Check that the loss in the receive path (receive loss), when break-in occurs, corresponds to the design value ofthe echo suppressor when the level applied at the receive-in port is in the
29、range 15 dBm0 to 20 dBm0.3.1.4 Check of signalling disablingThe operation and release of the signalling disable circuit should be checked.3.1.5 Check of tone disablingThe characteristics of the tone disabler circuit should be checked and should be within the following limits:a) Disabler sensitivityT
30、he disabler should operate for any single frequency within the disabling design range at a level of 30 dBm0. The disabler should be released when the disabling tone is reduced to a level of 36 dBm0.b) Broadband holding and releaseOnce disabled, a 31 dBm0 signal of 1020 Hz or a corresponding bit sequ
31、ence should hold disabling anda 36 dBm0 signal should not.3.2 The following characteristic times should be measured and should be within the limits shown:3.2.1 Suppressiona) Suppression operate time: 1 ms (see Note under 3.2.2).b) Suppression hangover time: 24-36 ms.3.2.2 Break-in (LR =constant)See
32、Table 1/M.660.4 Fascicle IV.1 Rec. M. 660TABLE 1/M.660Time Conditions For Break-In3.2.3 Tone disabilitya) Tone disabler operate time: 300 100 ms.b) Tone disabler hangover time: 250 150 ms (release time).Note The disabler should not release for breaks of less than 100 ms in the disabling tone (for de
33、finitions ofterms, see Recommendation G.164 3).3.3 Adaptive functionIf the echo suppressor incorporates the adaptive function, the following test should be made:Check that the break-in sensitivity of the echo suppressor increases at a speed of at least 4 dB/s during thephase of convergence if a leve
34、l greater than 20 dBm0 is applied to the input of the receive equipment.3.4 ConsequenceIf an echo suppressor is found not to comply with one of these tests, it should be taken out of service.References1 CCITT Recommendation Semi-automatic in-circuit echo suppressor testing system (ESTS), Vol. IV, Re
35、c O.25.2 CCITT Recommendation Echo suppressors suitable for circuits having either short or long propagation times,Orange Book, Vol. III, Rec. G.161, ITU, Geneva, 1977.3 CCITT Recommendation Echo suppressors, Vol. III, Rec. G.164.Function Operate times Hangover timesPartial break-in 2 ms (see Note)
36、26 msFull break-in 6-10 ms 48-66 msL: Level of signal at receive-in ports.Note Some types of built-in processor-controlled digital test systems use scanning periodsin excess of these values (for example, 4 ms) and would therefore affect the measuredvalues. It is for Administrations using such test systems to assess the impact of thisambiguity and to determine the need for any supplementary tests.
