1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/&G0G0$)4!,G0G042!.3-)33)/.3934%-34%2-).!,G0G0%15)0-%.43#(!2!#4%2)34)#3G0G0/&G0G03%#/.$G0G0/2$%20#-G0G0-5,4)0,%8G0G0%15)0-%.4G0G0/0%2!4).!4G0G0 G0KBIT S)45G134G0G0RecommendationG0G0 (Extrac
2、t from the “LUEG0“OOK)NOTES1 ITU-T Recommendation G.746 was published in Fascicle III.4 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
3、 Book version 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 m
4、ay be reproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.4 - Rec. G.746 1Recommendation G.746Fascicle III.4 - Rec. G.746CHARACTERISTICS OF SECOND ORDER PCM MULTIPLEXEQUIPMENT OPERA
5、TING AT 6312 kbit/s(Malaga-Torremolinos, 1984)1 General characteristics1.1 Fundamental characteristicsThe encoding law used is the -law as specified in Recommendation G.711. The sampling rate, load capacityand the code are also specified in that Recommendation.The number of quantized values is 255.
6、Two character signals are reserved for zero value (11111111 and01111111).In some networks the all 0 character signal (00000000) is eliminated to avoid loss of timing information to thedigital line, resulting in 254 quantized values.1.2 Bit rateThe nominal bit rate is 6312 kbit/s. The tolerance on th
7、is rate is 30 parts per million (ppm).1.3 Timing signalIt should be possible to derive the transmitting timing signal of a PCM multiplex equipment from an internalsource, from the incoming digital signal and also from an external source.2 Frame structureRefer to 3.2.1 and 3.2.2 of Recommendation G.7
8、04 for frame structure and use of derived channel time slots.3 Loss and recovery of frame alignmentThe strategy for the loss and recovery of frame alignment should be according to Rec. G.706, 3.1.4 Fault conditions and consequent actions4.1 Fault conditionsThe PCM multiplex equipment should detect t
9、he following conditions:4.1.1 Failure of power supply.4.1.2 Loss of incoming signals at 6312 kbit/s.4.1.3 Loss of frame alignment.4.1.4 Alarm indication received from the remote PCM multiplex equipment.2 Fascicle III.4 - Rec. G.7464.2 Consequent actionsFurther to the detection of a fault condition,
10、appropriate actions should be taken as specified in Table 1/G.746.The consequent actions are as follows:4.2.1 A service alarm indication should be generated to signify that the service provided by the PCM multiplex is nolonger available. This indication should be forwarded to the switching and/or si
11、gnalling equipment depending upon thearrangement provided.TABLE 1/G.746Fault conditions and consequent actions for the PCM multiplex equipmentConsequent actionsEquipmentpartFault condition Service alarmindicationgeneratedPromptmaintenancealarm indicationgeneratedAlarm indicationto the remote endgene
12、ratedTransmissionsuppressed at theanalogue outputsMultiplexer anddemultiplexerFailureof power supplyYes Yes Yes(if practicable)OptionalLoss of incoming signalat 6312 kbit/sYes Yes Yes YesDemultiplexeronlyLoss of framealignmentYes Yes Yes YesAlarm indicationreceived fromthe remote endOptional Yes Opt
13、ionalNote 1- A Yes in the table signifies that a certain action should be taken as a consequence of the relevant fault condition. An openspace in the table signifies that the relevant action should not be taken as a consequence of the relevant fault condition, if thiscondition is the only one presen
14、t. If more than one fault condition is simultaneously present the relevant action should be taken if, forat least one of the conditions, a Yes is defined in relation to this action.Note 2 - Indications of additional fault conditions, such as codec failure and excessive bit errors, are left to the di
15、scretion of individualAdministrations.4.2.2 The service alarm described in 4.2.1 above should be used to automatically remove the associated circuitsfrom service and to restore them to service when frame alignment has been recovered.Note - The removal of the associated circuits described in 4.2.2 ab
16、ove should be done in such a way that thecircuits are not needlessly removed in the case of a brief isolated loss of frame alignment but are removed in the case ofa permanent or intermittent loss of frame alignment.It is also important to minimize the impact of signalling errors which may occur duri
17、ng periods of loss of framealignment. These functions should be provided in the PCM multiplex equipment or in the switching/signallingequipment.4.2.3 A prompt maintenance alarm indication should be generated to signify that performance is below acceptablestandards and maintenance attention is requir
18、ed locally.Fascicle III.4 - Rec. G.746 34.2.4 An alarm indication to the remote end should be generated by forcing bit a to the value 1.4.2.5 Transmission should be suppressed at the analogue outputs.4.2.6 Rapid indication of loss of frame alignmentAn indication should be given to the Signalling Sys
19、tem No. 6 equipment (digital version) when the PCMmultiplex equipment (local end only) detects a loss of frame alignment. The average time to detect and give an indicationof random bits in the frame alignment signal bit positions should not be greater than 3 ms. This indication will serve thesame fu
20、nction as that provided by the data carrier failure alarm in the analogue version (see Recommendation Q.2751).5 Signalling5.1 Signalling arrangementRefer to 3.2.3 of Recommendation G.704.5.2 Loss of multiframe alignment in case of channel associated signallingLoss of multiframe alignment is assumed to have taken place when loss of frame alignment occurs.6 InterfacesAnalogue: Refer to Recommendations G.712, G.713 and G.714.Digital: Refer to Recommendation G.703.Reference1 CCITT Recommendation Data channel failure detection, Vol. VI, Rec. Q.275.
