1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/- the number of bits per frame;- the bit numbering scheme;- the bit assignment;- the bunched frame alignment signal.2 Fascicle III.4 - Rec. G.753TABLE 1/G.75334 368-kbit/s multiplexing fra
2、me structure using positive/zero/negative justificationTributary bit rate (kbit/s) 8448Number of tributaries 4Frame structure Bit numberFrame alignment signal (111110100000)Bits from the secondary tributariesJustification control bits (Cj1)Bits for service functionsJustification control bits (Cj2)Bi
3、ts from the secondary tributariesJustification control (Cj3)Bits reserved for national useBits from tributaries available for negative justificationBits from tributaries available for positive justificationBits from the tributariesSet I1 to 1213 to 716Set II1 to 45 to 89 to 1213 to 716Set III1 to 45
4、 to 89 to 1213 to 1617 to 716Frame lengthFrame durationBits per tributaryMaximum justification rate per tributary2148 bits62.5 s52816 kbit/sNote - Cjnindicates the nth justification control pulse of the jth tributary.4 Loss and recovery of frame alignment and consequent actionsThe frame alignment sy
5、stem should be adaptive to the error ratio in the line link. Until frame alignment isrestored the frame alignment system should retain its position. A new search for the frame alignment signal should beundertaken when three or more consecutive frame alignment signals have been incorrectly received i
6、n their positions.Frame alignment is considered to have been recovered when more than two consecutive frame alignmentsignals have been correctly received in their predicted positions.5 Multiplexing methodCyclic bit interleaving in the tributary numbering order and positive-negative justification wit
7、h two-commandcontrol are recommended. The justification control signal should be distributed and use Cjn-bits (n = 1, 2, 3 seeTable 1/G.753). Correction of one error in a command is possible.Positive justification should be indicated by the signal 111, transmitted in each of two consecutive frames;n
8、egative justification should be indicated by the signal 000, transmitted in each of two consecutive frames, and nojustification by the signal 111 in one frame followed by 000 in the next frame.Fascicle III.4 - Rec. G.753 3Digit time slots 9, 10, 11, 12 (Set III) are used for information carrying bit
9、s (for negative justification), and digittime slots 13, 14, 15, 16 in Set III when it is necessary are used for no information carrying bits (for positivejustification) for the tributaries 1, 2, 3, 4.Besides, when information from tributaries 1, 2, 3 and 4 is not transmitted, bits 9, 10, 11 and 12 i
10、n Set III areavailable for transmitting information concerning the type of justification (positive or negative) in frames containingcommands of positive justification control and intermediate amount of jitter in frames containing commands of negativejustification.Table 1/G.753 gives maximum justific
11、ation rate per tributary.6 JitterThe amount of jitter that should be tolerated at the input of the multiplexer and the demultiplexer should beaccording to 3.1.1/G.823. The amount of jitter at the output of the multiplexer and the demultiplexer should be studiedand specified.7 Digital interfaceThe in
12、terface at the nominal bit rate 34 368 kbit/s is under study.8 Timing signalThe clock should be able to be controlled by an external source.9 Service digitsSome spare bits per frame are available for service functions (bits 5, 6 and 8 in Set II) for national andinternational use. Bits 5 and 6 in Set
13、 II are available for a digital service channel (using 32 kbit/s Adaptive DeltaModulation) and bit 8 in Set II is available for ringing up a digital service channel.10 Fault conditions and consequent actions10.1 The digital multiplex equipment should detect the following fault conditions:10.1.1 Fail
14、ure of power supply.10.1.2 Loss of the incoming signal at 8448 kbit/s at the input of the multiplexer.Note - When using separate circuits for the digital signal and the timing signal, loss of either or both of themshould constitute loss of the incoming signal.10.1.3 Loss of the incoming signal at 34
15、 368 kbit/s at the input of the demultiplexer.Note - The 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 34 368 kbit/s inpu
16、t of the demultiplexer(see 10.2.2 below).4 Fascicle III.4 - Rec. G.75310.2 Consequent actionsAfter detecting a fault condition, appropriate actions should be taken as specified in Table 2/G.753. Theconsequent actions are as follows:10.2.1 Prompt maintenance alarm indication generated to signify that
17、 the performance is below acceptable standardsand maintenance attention is required locally. When detecting the Alarm Indication Signal (AIS) at the 34 368 kbit/sinput of the demultiplexer the prompt maintenance alarm indication associated with loss of frame alignment should beinhibited (see Note 1
18、below).Note - The location and provision of any visual and/or audible alarm 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 the state 1 bit 7of Se
19、t II at the 34 368 kbit/s output of the multiplexer.10.2.3 AIS (see Note 2 below) applied to all four outputs of the 8448 kbit/s tributary outputs from the demultiplexer.10.2.4 AIS (see Note 2 below) applied to the 34 368 kbit/s output of the multiplexer.10.2.5 AIS (see Note 2 below) applied to the
20、time slots of the 34 368 kbit/s signal at the multiplexer outputcorresponding to the relevant 8448 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 eq
21、uivalent binary content of the AIS at 8448 kbit/s and 34 368 kbit/s is a continuous stream ofbinary 1s.TABLE 2/G.753Fault conditions and consequent actionConsequent actions (see 10.2)AIS appliedEquipmentpartFault conditions(see 10.1)PromptmaintenancealarmindicationgeneratedAlarmindication tothe remo
22、temultiplexergeneratedTo alltributariesTo thecompositesignalTo the releventtime slotsof thecompositesignalMultiplexeranddemultiplexerFailureof power supplyYes Yes, ifpracticableYes, ifpracticableYes, ifpracticableMultiplexeronlyLoss of incoming signalon a tributaryYes YesLoss of incoming signalat 34
23、 368 kbit/sYes Yes YesDemultiplexer Loss of frame alignment Yes Yes Yesonly AIS 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.
