1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/&G0G0$)4!,G0G042!.3-)33)/.3934%-34%2-).!,G0G0%15)0-%.43#(!2!#4%2)34)#3G0G0/&G0G039.#(2/./53$)4!,G0G0-5,4)0,%8G0G0%15)0-%.4/0%2!4).G0G0!4G0G0 G0KBIT S)45G134G0G0RecommendationG0G0 (Extract
2、from the “LUEG0“OOK)NOTES1 ITU-T Recommendation G.734 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 B
3、ook 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 may
4、 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.734 1Recommendation G.734Fascicle III.4 - Rec. G.734CHARACTERISTICS OF SYNCHRONOUS DIGITAL MULTIPLEXEQUIPMENT OPER
5、ATING AT 1544 kbit/s(former Recommendation G.736 of Volume III of the Yellow Book)1 General characteristicsThis Recommendation defines the characteristics of a synchronous multiplex equipment currently used forapplications in dedicated data networks, to combine up to 23 tributary channels at 64 kbit
6、/s in a 1544 kbit/s digitalstream.Note - For applications within an ISDN, it is expected that a 24-channel multiplex will be used that has a framestructure conforming to Recommendation G.733.1.1 Bit rateThe nominal bit rate is 1544 kbit/s.Note - The tolerance on this rate should be studied and speci
7、fied.1.2 Timing signalsIt should be possible to derive the multiplexer timing signals from the composite clock signal of a centralizedclock source as specified in Recommendation G.703, and from the 1544 kbit/s incoming digital stream.Note - The desirability of also providing a 1544 kHz transmitting
8、timing signal from a centralized clock sourceshould be further studied.2 Frame structure2.1 Number of bits per channel time slotThere are eight bits per channel time slot, numbered from one to eight.2.2 Number of channel time slots per frameThere are 24 time slots per frame, numbered from 1 to 24. S
9、uccessive bits for bytes 1 to 24 should beconsecutively numbered from 2 to 193. The first bit should be reserved for optional use. The frame repetition rate is8000 Hz.2.3 Channel time slot assignment2.3.1 Channel time slots 1 to 23 are assigned to tributaries.2.3.2 Channel time slot 24 is assigned t
10、o frame alignment and service digits. Two alternative methods, as given inTables 1/G.734 and 2/G.734 for allocation of these signals and associated frame alignment strategy are recommended.2 Fascicle III.4 - Rec. G.734TABLE 1/G.734Allocation of time slot 24, Method 1Bit number of time slot 241234567
11、8Service digitsFrame alignment signal10111 0Note - Loss of frame alignment should be assumed to have taken place when more than three of twelve successiveframes have an error in the frame alignment signal and/or in bit 1 of the 193-bit frame. Frame alignment should beassumed to have been recovered w
12、hen four consecutive correct frame alignment signals have been received.TABLE 2/G.734Allocation of time slot 24, Method 2Frame Number Bit number of time slot 24123456781 ServicedigitsFrame alignmentsignal001012 11010Note - Loss of frame alignment should be assumed to have taken place when seven cons
13、ecutive pairs of the frame alignmentsignal (00101, 11010) have been incorrectly received in their predicted positions. Frame alignment should be assumed to havebeen recovered when two consecutive correct pairs of frame alignment signals have been received.2.4 Service digitsThe use of service digits
14、in channel time slot 24 is under study.Note - The first bit could be considered for framing algorithms.Fascicle III.4 - Rec. G.734 33 Fault conditions and consequent action3.1 Fault conditionsThe digital multiplex equipment should detect the following fault conditions:- failure of power supply,- los
15、s of the incoming signal at 1544 kbit/s,- loss of frame alignment,- loss of timing signals supplied from the centralized clock,- alarm indication received from the remote digital multiplex equipment.Some of the above fault conditions may optionally be detected by auxiliary equipment normally used in
16、association with the digital multiplex equipment.3.2 Consequent actionsFurther to the detection of a fault condition, appropriate actions should be taken as specified in Table 3/G.734.TABLE 3/G.734Fault conditions and consequent actions for the digital multiplex equipmentConsequent action(see Notes
17、1 and 2)Equipment part Fault conditionsPromptmaintenance alarmindication generatedAlarm indication tothe remote endtransmitted(see Note 3)Multiplexout-of sync signalapplied to 64 kbit/soutput(see Note 4)Multiplexer anddemultiplexerFailure of power supply YesYes(if practicable)Yes(if practicable)Loss
18、 of incoming signal at1544 kbit/sYes Yes YesDemultiplexer only Loss of frame alignment Yes Yes YesAlarm indication receivefrom the remote endYesNote 1 - A Yes in the table signifies that an action should be taken as a consequence of the relevant fault condition. An openspace in the table signifies t
19、hat the relevant action should not be taken as a consequence of the relevant fault condition, if thiscondition is the only one present. If more than one fault condition is simultaneously present, the relevant action should be takenif, for at least one of the conditions, a Yes is defined in relation
20、to this action.Note 2 - These consequent actions may optionally be taken by auxiliary equipment normally used in conjunction with the digitalmultiplex equipment.Note 3 - The alarm indication to the remote end may be generated by changing a service bit of time slot 24 from the state 1 to thestate 0,
21、if possible.Note 4 - The binary content of the multiplex out-of-sync signal is under study. One Administration uses 00011010.4 Fascicle III.4 - Rec. G.7344 Multiplexing methodCyclic byte interleaving in the tributary numbering order should be used. The digital multiplex equipmentshould translate any
22、 incoming byte that contains only 0s into the zero byte suppression code.Note 1 - The content of the zero byte suppression code is under study.Note 2 - Further study is needed for the case when the zero suppression code must be extracted.5 Input jitter and wanderThe amount of jitter and wander that should be tolerated at the input of the demultiplexer should be accordingto Recommendation G.824, 3.1.1.6 Digital interfaceThe digital interface at 64 kbit/s and 1544 kbit/s should be in accordance with Recommendation G.703.
