1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 / TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#)&)#!4)/.3G0G0&/2G0G0-%!352).G0G0%15)0-%.4).G1334!4)/.G0G0%#(/G0G0#!.#%,%2G0G04%34%15)0-%.4)45G134G0G0RecommendationG0G0 (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation O.27 was published in Fasc
2、icle IV.4 of the Blue Book. This file is an extract from theBlue 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 version and copyright conditions remain unchanged (see below).2 In this
3、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 reproduced or utilized in any form or by any means, electronic ormechani
4、cal, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.4 - Rec. O.27 1Recommendation O.27Fascicle IV.4 - Rec. O.27INSTATION ECHO CANCELLER TEST EQUIPMENT(Melbourne, 1988)1 GeneralThe in-station echo canceller test equipment (ISET) is intended to test type C
5、 and D echo cancellers includingtone disablers as specified in Recommendation G.165 1. Two test modes are provided as described below. The testsperformed in each test mode are listed in Table 1/O.27.2 Test modes2.1 Routine test modeIn this test mode, ISET provides 7 simplified tests of echo cancelle
6、r performance under normal circuitconditions with the adaptation and non-linear processing logic activated. Access to the echo canceller being tested is ona 4-wire basis, and these simple performance tests are made by applying test signals to the receive-in (Rin) and thesend-in (Sin) ports of the ec
7、ho canceller. Test results are measured at the send-out (Sout) port. A functional blockdiagram of the test arrangement is shown in Figure 1/O.27.FIGURE 1/O.27Functional block diagram of test arrangement2.2 Diagnostic test modeIn this mode, all performance tests are made according to procedures speci
8、fied in Recommendation G.1651. The adaptation and non-linear processing logic is disabled when necessary by controlling the echo canceller that isbeing tested.2 Fascicle IV.4 - Rec. O.273 Operating principles3.1 Method of accessWhen an echo canceller to be tested is fitted to a particular circuit, a
9、 reserved echo canceller should besubstituted so that the tests can be made without causing any disturbance to the circuit. If no reserved echo canceller isavailable, the circuit should be blocked from service while the tests are being performed.ISET may be connected to an echo canceller under test
10、either manually at local access points or remotely byaccess arrangements through a switching system. Administrations may wish to provide remote access capability to echocancellers for routine tests as shown in Figure 2/O.27. Local access as shown in Figure 3/O.27 is for diagnostic testswhere the use
11、 of control signals to inhibit the H register, adaptation and center clipper logic are needed.FIGURE 2/O.27Configuration for routine test modeAI Adaptation inhibitHC H register clearCO Centre clipper offEC Echo cancellerISET In-station echocanceller testerFIGURE 3/O.27Configuration for diagnostic te
12、st modeFascicle IV.4 - Rec. O.27 33.2 Testing sequencesWhen access has been established, a series of tests is performed manually or automatically. The tests to beperformed in the routine and diagnostic test modes are given in Table 1/O.27. Measurement results for each test shallbe provided to the ma
13、intenance personel by a visual display or printed message.If an echo canceller fails any of the routine tests, it should be completely tested in the diagnostic test mode.TABLE 1/O.27Test ProceduresNo. Type of TestG.165 1Test modesReferenceRoutine Diagnostic1 Steady state residual and returned echo l
14、evel test 3.4.2.1 0 02 Convergence test 3.4.2.2 0 03 Double talk detection oversensitivity test 3.4.2.3.1 0 04 Double talk detection undersensitivity test 3.4.2.3.2 0 05 Leak rate test 3.4.2.4 06 Infinite return loss convergence test 3.4.2.5 0 07 Tone disabler send side sensitivity test 4.2 0 08 Ton
15、e disabler receive side sensitivity test 4.2 0 09 Tone disabler guard band test 4.3 010 Tone disabler holding band test 4.4 011 Tone disabler operate time test 4.5 012 Tone disabler release time test 4.8 013 External disabler control test 3.3 04 Test procedures and test requirements4.1 Routine test
16、modeFigure 1/O.27 shows a functional arrangement for the routine test mode. The following seven tests should berepeated with an appropriate echo path delay ms1set in the adjustable echo delay unit.At the beginning of each of the seven tests, a conditioning tone is applied for 1 second to the Rinport
17、 forinitialization of the echo canceller to be tested. The conditioning tone is a 2100 Hz signal of 10 dBm0 with periodicphase reversals occurring every 0.45 seconds and is also used to disable echo cancellers. During this initializationperiod the H register of the canceller is cleared. After the co
18、nditioning tone is disconnected, no signal is applied to thecanceller for at least 0.4 seconds to allow it to return to an enabled state. Further information on the characteristics ofecho canceller tone disablers may be found in 4 and Annex B of Recommendation G.165 1._1Different echo cancellers may
19、 be designed to work satisfactorily for different echo path delays depending on their application invarious networks. Thus represents the echo path delay for which the echo canceller is designed. Each Administration may choosea delay value of appropriate for their equipment.4 Fascicle IV.4 - Rec. O.
20、274.1.1 Check of steady state residual and returned echo levelStep 1: A random noise signal (A) of 10 dBm0 is applied to the Rinport. With the echo path loss setat 10 dB, an echo appears at the Sinport.Step 2: After 2 seconds the returned echo level at the Soutport is measured.Requirement: The retur
21、ned echo level must be less than 65 dBm0.4.1.2 Check of convergenceStep 1: A random noise signal (A) of 10 dBm0 is applied to the Rinport. With the echo path loss setat 6 dB, an echo is appears at the Sinport.Step 2: A second random noise signal (B) of 10 dBm0 is applied to the Sinport as shown in F
22、igure1/O.27.Step 3: After 0.5 seconds noise signal (B) is disconnected, and 0.5 seconds later the returned signallevel at the Soutport is measured.Requirement: The signal level must be less than 37 dBm0.4.1.3 Check of double talk detection oversensibilityStep 1: A random noise signal (A) of 10 dBm0
23、is applied to the Rinport. With the echo path loss setas 6 dB, an echo appears at the Sinport.Step 2: After 0.5 seconds, a second random noise signal (B) of 25 dBm0 is applied to the Sinport.Step 3: One second later noise signal (B) is disconnected and the returned echo level at the Soutport ismeasu
24、red.Requirement: The returned echo level must be less than 25 dBm0.4.1.4 Check of double talk detection undersensitivityStep 1: With the echo path loss set at 10 dB, a random noise signal (A) of 10 dBm0 is applied to theRinport.Step 2: After 1 second the noise signal (A) at the Rinport is disconnect
25、ed.Step 3: After an interval of 0.5 seconds, the noise signal (A) is reapplied to the Rinport.Simultaneously a second noise signal (B) of 0 dBm0 is applied to the Sinport.Step 4: 0.5 seconds later the noise signal (B) is disconnected and the residual echo level at the Soutport is measured.Requiremen
26、t: The returned echo level must be less than 26 dBm0.4.1.5 Check of infinite return loss convergenceStep 1: With the echo path loss set at 6 dB, a random noise signal (A) of 10 dBm0 is applied to theRinport.Step 2: After 1 second the echo path between Routand Sinis disconnected while noise signal (A
27、)remains connected to the Rinport.Step 3: 0.5 seconds later the returned echo level at the Soutport is measured.Requirement: The returned echo level must be less than 37 dBm0.4.1.6 Check of tone disabler send-side sensitivityThere are two parts to this test to ensure that the disabler tone detection
28、 circuit on the send side is notoversensitive or undersensitive.Step 1: A 2100 Hz signal of 36.5 dBm0 with periodic phase reversals every 0.45 seconds is appliedfor one second to the Sinport.Step 2: A random noise signal (A) of 10 dBm0 is applied to the Rinport.Step 3: After 0.5 seconds the returned
29、 echo level at the Soutport is measured.Requirement: The returned echo level must be less than 32 dBm0 to show that the disabler is not operated.Fascicle IV.4 - Rec. O.27 5Step 4: The conditioning tone is reapplied for one second to the Rinport. After at least 0.4 seconds,the 2100 Hz signal with per
30、iodic phase reversals every 0.45 seconds is reapplied to the Sinportat a level of 29.5 dBm0 for one second.Step 5: Then the random noise signal (A) of 10 dBm0 is reapplied to the Rinport with the echo pathloss set at 10 dB.Step 6: After 0.5 seconds the returned echol level at the Soutport is measure
31、d.Requirement: The returned echo level must be between 29.5 dBm0 and 26.5 dBm0 to show that thedisabler is operated.4.1.7 Check of tone disabler receive-side sensitivityThere are also two parts to this test to ensure that the disabler tone detection on the receive side is notoversensitive or underse
32、nsitive.Step 1: A 2100 Hz signal of 36.5 dBm0 with period periodic phase reversals every 0.45 seconds isapplied for one second to the Rinport.Step 2: A random noise signal (A) of 10 dBm0 is applied to the Rinport. With the echo path loss setat 10 dB, an echo appears at the Sinport.Step 3: After 0.5
33、seconds the returned echo level at the Soutport is measured.Requirement: The returned level must be less than 32 dBm0 to show that the disabler is not operated.Step 4: The conditioning tone is reapplied for one second to the Rinport. After at least 0.4 seconds,the 2100 Hz signal with periodic phase
34、reversals every 0.45 seconds is reapplied to the Sinportat a level of 29.5 dBm0 for one second.Step 5: Then the random noise signal (A) of 10 dBm0 is reapplied to the Rinport with the echo pathloss set at 10 dB.Step 6: After 0.5 seconds the returned echo level at the Soutport is measured.Requirement
35、: The returned echo level must be between 29.5 dBm0 and 26.5 dBm0 to show that thedisabler is operated.4.2 Diagnostic test modeIn this mode diagnostic tests are performed as specified in Recommendation G.165. 3.3.2 and 4 1.5 Specifications for transmission measuring equipmentThe following specificat
36、ions apply for climatic conditions specified in Recommendation O.3.5.1 Signal generator5.1.1 Range of frequency0.3 to 3.4 kHz in 0.01 kHz steps.5.1.2 Range of level40 to 0 dBm0 in 0.1 dB steps.5.1.3 AccuracyFrequency 0.01 kHzLevel 0.1 dB.5.2 Level meter5.2.1 Range of measurement70 to + 3.2 dBm0.5.2.
37、2 Accuracy 0.1 dB (above 40 dBm0).6 Fascicle IV.4 - Rec. O.275.2.3 Dynamic response timeUnder study2.5.3 Random noise source5.3.1 Level40 to + 0 dBm0.5.3.2 Noise signalThe noise test signal is a band-limited white noise (300 3400 Hz).5.4 Echo path5.4.1 Echo loss0 dB to 40 dB in 0.1 dB steps.5.4.2 Ec
38、ho delay0 to ms3in 1 ms steps.5.4.3 Bandwidth0.3 to 3.4 kHz.6 Calibration6.1 Calibration of measuring equipmentCalibration features should be provided to check that the accuracy requirements are met.6.2 Self-check of operational functionA local self-checking facility should be provided to make sure
39、that the testing functions are operatingproperly.7 Optional arrangements7.1 Automatic test functionA function to perform tests in sequence automatically according to the predetermined procedure, may beprovided.7.2 Automatic start functionA timed automatic start function which enables the unattended
40、operations, may be provided.References1 CCITT Recommendation Echo Cancellers, Vol. III, Rec. G.165._2A meter with a rapid response time will be needed to meet the timing requirements of some of the tests specified above.3Different echo cancellers may be designed to work satisfactorily for different echo path delays depending on their application invarious networks. Thus represents the echo path delay for which the echo canceller is designed. Each Administration maychoose a delay value of appropriate for their equipment.
