1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/ further amended)1 GeneralThe fourth order digital multiplex system with positive/zero/negative pulse justification as given below isintended for use on digital connection between countrie
2、s having the same type of justification using any third orderdigital systems at 34 368 kbit/s.2 Bit rateThe nominal bit rate should be 139 264 kbit/s. The tolerance on that rate should not be more than 15 parts permillion (ppm).3 Frame structureTable 1/G.754 gives:- the tributary bit rate and the nu
3、mber of tributaries;- the number of bits per frame;- the bit numbering scheme;- the bit assignment;- the bunched frame alignment signal.TABLE 1/G.754139 264-kbit/s multiplexing frame structure using positive/zero/negative justificationTributary bit rate (kbit/s) 34 368Number of tributaries 4Frame st
4、ructure Bit numberFrame alignment signalBits for service functionsBits from tributariesJustification control bit (Cj1)Bits from tributariesJustification control bit (Cj2)Bits from tributariesJustification control bit (Cj3)Bits from tributaries available for negative justificationBits from tributarie
5、s available for positive justificationBits from tributariesSet I1 to 1011 to 1213 to 544Set II1 to 45 to 544Set III1 to 45 to 544Set IV1 to 45 to 89 to 1213 to 544Frame lengthFrame durationBits per tributariesMaximum justification rate per tributary2176 bits15.625 s53764 kbit/sNote - Cjnindicates th
6、e nth justification control bit of the jth tributary.2 Fascicle III.4 - Rec. G.7544 Loss and recovery of frame alignment and consequent actionThe frame alignment system should be adaptive to the error rate in the line link. Until frame alignment isrestored the frame alignment system should retain it
7、s position. A new search for the frame alignment signal should beundertaken when three and more consecutive frame alignment signals have been incorrectly received in their position.Frame alignment is considered to have been recovered when more than two consecutive frame alignmentsignals have been co
8、rrectly received in their predicted positions.5 Multiplexing methodCyclic bit interleaving in the tributary numbering order and positive-negative justification with two commandcontrol are recommended. The justification control signal should be distributed and use Cjn-bits (n = 1, 2, 3 seeTable 1/G.7
9、54). Correction of one symbol error in a command is possible.Positive justification should be indicated by the signal 111, transmitted in each of two consecutive frames;negative justification should be indicated by the signal 000, transmitted in each of two consecutive frames, and nojustification by
10、 the signal 111 in one frame followed by 000 in the next frame.Digit time slots 5, 6, 7, 8 (Set IV) are used for information carrying bits (for negative justification), and digittime slots 9, 10, 11, 12 in Set IV, when it is necessary, are used for no information carrying bits (for positivejustifica
11、tion) for the tributaries 1, 2, 3, 4.Besides, when information from tributaries 1, 2, 3 and 4 is not transmitted, bits 5, 6, 7 and 8 in Set IV areavailable for transmitting information concerning the type of justification (positive or negative) in frames containingcommands of positive justification
12、control and intermediate amount of jitter in frames containing commands of negativejustification.Table 1/G.754 gives maximum justification rate per each third order tributary.6 JitterThe amount of jitter that should be accepted at the inputs of the demultiplexer and multiplexer and should be atthe o
13、utput of the demultiplexer is under study.7 Digital interfaceThe interface at the nominal bit rates 34 368 kbit/s and 139 264 kbit/s is under study.8 Timing signalThe clock should be able to be controlled by an external source.9 Service functionsSome spare bits per frame are available for service fu
14、nctions (bits 11 and 12 in Set I) for national andinternational use. Bit 11 in Set I is available for a digital service channel (using 32 kbit/s Adaptive Delta Modulation)and bit 12 is available for ringing up a digital service channel.10 Fault conditions and consequent actions10.1 The digital multi
15、plex equipment should detect the following fault conditions:10.1.1 Failure of power supply.Fascicle III.4 - Rec. G.754 310.1.2 Loss of the incoming signal at 34 368 kbit/s at the input of the multiplexer.10.1.3 Loss of the incoming signal at 139 264 kbit/s at the input of the demultiplexer.Note - Th
16、e detection of this fault condition is required only when it does not result in an indication of loss offrame alignment.10.1.4 Loss of frame alignment.10.1.5 Alarm indication received from the remote multiplex equipment at the 139 264 kbit/s input of thedemultiplexer (see 10.2.2 below).10.2 Conseque
17、nt actionsAfter detection of a fault condition appropriate actions should be taken as specified in the Table 2/G.754. Theconsequent actions are as follows:10.2.1 Prompt maintenance alarm indication generated to signify that the performance is below acceptable standardsand maintenance attention is re
18、quired locally. When detecting the Alarm Indication Signal (AIS) at the 139 264 kbit/sinput of the demultiplexer the prompt maintenance alarm indication associated with loss of frame alignment should beinhibited (see Note 1 below).Note - The location and provision of any visual and/or audible alarm
19、activated by this prompt maintenancealarm indication is left to the discretion of each Administration.10.2.2 Alarm indication to the remote multiplex equipment generated by changing from the state 0 to thestate 1 bit 12 of Set I at the 139 264 kbit/s output of the multiplexer.10.2.3 AIS (see Note 2
20、below) applied to all the four outputs of the 34 368 kbit/s tributary outputs from thedemultiplexer.10.2.4 AIS (see Note 2 below) applied to the 139 264 kbit/s output of the multiplexer.10.2.5 AIS (see Note 2 below) applied to the time slots of the 139 264 kbit/s signal at the multiplexer outputcorr
21、esponding to the relevant 34 368 kbit/s tributary.Note 1 - The bit rate of the AIS at the output of the corresponding demultiplexer should be as specified for thetributaries. The method of achieving this is under study.Note 2 - The equivalent binary content of the AIS at 34 368 kbit/s and 139 264 kb
22、it/s is a continuous stream ofbinary 1s.4 Fascicle III.4 - Rec. G.754TABLE 2/G.754Fault conditions and consequent actionsConsequent actions (see 10.2)AIS appliedEquipmentpartFault condition(see 10.1)PromptmaintenancealarmindicationgeneratedAlarmindication tothe remotemultiplexergeneratedTo alltribut
23、ariesTo thecompositesignalTo the relevanttime slotsof thecompositesignalMultiplexeranddemultiplexerFailureof power supplyYesYes, ifpracticableYes, ifpracticableYes, ifpracticableMultiplexeronlyLoss of incoming signalon a tributaryYes YesLoss of incoming signalat 139 264 kbit/sYes Yes YesDemultiplexe
24、ronlyLoss of frame alignment Yes Yes YesAIS received fromthe remote multiplexerNote - A Yes in the table signifies that a certain action should be taken as a consequence of the relevant fault condition. Anopen space in the table signifies that the relevant action should not be taken as a consequence of the relevant fault condition,if this condition is the only one present. If more than one fault condition is simultaneously present the relevant action shouldbe taken if, for at least one of the conditions, a Yes is defined in relation to this action.
