1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/ i = 1, 2, 3) (see Note 5 toTable 1/G.747).Positive justification should be indicated by the justification control signal 111 and no justification by the signal000. Majority decision is re
2、commended.Table 1/G.747 gives the maximum justification rate per tributary and the nominal justification ratio.2 Fascicle III.4 - Rec. G.747TABLE 1/G.7476312 kbit/s multiplexing frame structureNominal tributary bit rate (kbit/s) 2048Number of tributaries 3Frame structure Bit numberFrame alignment si
3、gnal (111010000)Bits from tributariesAlarm indication to the remote multiplex equipment (Note 1)Parity bit (Notes 2 and 3)Bit reserved for future use (Note 4)Bits from tributariesJustification control bits Cj1 (Note 5)Bits from tributariesJustification control bits Cj2 (Note 5)Bits from tributariesJ
4、ustification control bits Cj3(Note 5)Bits from tributaries available for justificationBits from tributariesSet I1 to 910 to 168Set II1234 to 168Set III1 to 34 to 168Set IV1 to 34 to 168Set V1 to 34 to 67 to 168Frame lengthBits per tributary in a frameMaximum justification rate per tributaryNominal j
5、ustification ratio840 bits273 bits7.5 kbit/s0.453Note 1 - See 10.2.1.Note 2 - The parity bit = 1 if the number of marks in all tributary bits including the bits in the justifiabletime-slots in the preceding frame is odd; the parity bit = 0 if the number of marks in all tributary bitsincluding the bi
6、ts in the justifiable time-slots in the preceding frame is even.Note 3 - The implementation and the use of this parity bit procedure are for further study.Note 4 - This bit should be set to 1 when not used.Note 5 - Cji(j = 1, 2, 3; i = 1, 2, 3) indicates the ith justification control bit of the jth
7、tributary.6 jitter6.1 Muldex jitter transfer characteristicA 2048 kbit/s signal, modulated by sinusoidal jitter, should be subject to a muldex jitter transfer characteristicFascicle III.4 - Rec. G.747 3within the gain/frequency limits given in Figure 1/G.747. The equivalent binary content of the tes
8、t signal should be1000.Note - In addition, the need to specify a demultiplexer tributary jitter transfer characteristic from the 6312 kbit/sdemultiplexer input to the 2048 kbit/s demultiplexer output is for further study.Note - The frequency f0should be as low as possible, taking into account the li
9、mitations of measuringequipment. In any case, f0should be no greater than 10 Hz. The selective measurement method should beused.FIGURE 1/G.747Muldex jitter transfer characteristic6.2 Output jitter6.2.1 Tributary output jitterWith no jitter applied to the input ports of the multiplexer and with the m
10、ultiplexer directly connected to thedemultiplexer, the peak-to-peak jitter at the tributary output port should not exceed 0.2 UI over a measurement intervalof one minute in the frequency range from f0to 100 kHz (see Note 1).When measured with an instrument incorporating a bandpass filter having a lo
11、wer cutoff frequency of 18 kHz,a roll-off of 20 dB/decade and an upper limit of 100 kHz, the peak-to-peak output jitter should not exceed 0.05 UI whenmeasured over a one minute interval (see Note 2).Note 1 - The frequency f0should be as low as possible, taking into account the limitations of measure
12、mentequipment. In any case f0should be no greater than 10 Hz.Note 2 - For interfaces meeting the national high Q option, detailed in Recommendation G.823, the lower cutofffrequency for the above measurement should be 700 Hz.6.2.2 Multiplexer output jitterThe peak-to-peak jitter at the 6312 kbit/s ou
13、tput port should not exceed 0.05 UI when it is measured over oneminute interval within the frequency range from f1= 10 Hz to f4= 60 kHz.6.3 Input jitter6.3.1 Tributary input jitterThe 2048 kbit/s input port should be capable of accommodating levels of input jitter up to the limits given in4 Fascicle
14、 III.4 - Rec. G.747Rec. G.823.6.3.2 Demultiplexer input jitterThe 6312 kbit/s input port should be capable of accommodating levels of input jitter up to the limits given inFigure 2/G.747.Note 1 - Current Recommendation G.703 does not refer to the jitter tolerated at the digital distribution frame at
15、6312 kbit/s nor at the input port of equipment connected to this distribution frame.Note 2 - The jitter accommodation requirement should be met when the jittered input signal is composed of themultiplexed tributary signals having any value of jitter allowed for the 2048 kbit/s.Peak-to-peak sinusoida
16、ljitter amplitudeFrequencyA1 (UI) A2(UI) f1 (Hz) f2 (Hz) f3 (kHz) f4 (kHz)5.0 0.15 10 120 4 60FIGURE 2/G.747Lower limit of maximum tolerable sinusoidal input jitterat 6312 kbit/s7 Digital interfacesThe digital interfaces at 2048 kbit/s and 6312 kbit/s should be in accordance with Recommendation G.70
17、3.8 Timing signalIf it is economically feasible, it may be desirable to be able to derive the multiplexing timing signal from anexternal source as well as from an internal source.Fascicle III.4 - Rec. G.747 59 Service digitsThree bits per frame are available for service functions (see Table 1/G.747)
18、: bit 1 of Set II is used to transmit analarm indication to the remote multiplex equipment when specific fault conditions are detected in the multiplexequipment (see 10 below); bit 2 of Set II may be used for a parity check; bit 3 of Set II is reserved for future use.10 Fault conditions and conseque
19、nt actions10.1 Fault conditions10.1.1 The digital multiplex equipment should detect the following fault conditions:1) failure of power supply;2) loss of an incoming 2048 kbit/s tributary signal at a multiplexer input port;3) loss of an incoming 6312 kbit/s multiplex signal at a demultiplexer input p
20、ort;4) loss of frame alignment signal at a demultiplexer input port;5) detection of an alarm indication received from the remote multiplex equipment at a demultiplexer inputport;6) detection of alarm indication signal (AIS) at a demultiplexer input port.Note 1 - The equivalent binary content of the
21、AIS at 2048 and 6312 kbit/s should be a continuous stream ofbinary 1s (marks) as recommended in Recommendation M.20.Note 2 - Some current 44 736/6312 kbit/s demultiplexers do not issue a 6312 kbit/s AIS. Thus no detection cantake place in that case.Note 3 - The strategy for detecting the presence of
22、 the AIS should be such that the AIS is detectable even in thepresence of an error ratio of 1 10-3. However, a signal with all bits except the frame alignment signal in the state of 1should not be mistaken as an AIS.10.1.2 The need to monitor the degradation of the incoming 6312 kbit/s signal for th
23、e purpose of end-to-end errorperformance monitoring of the 6132 kbit/s digital block as well as the procedure for detecting such degradation, are forfurther study.10.2 Consequent actionsFurther to the detection of a fault condition, the appropriate actions should be taken as specified inTable 2/G.74
24、7.Note 1 - The concept and definition of prompt maintenance alarm indication is given in Recommendation M.20.Note 2 - When the alarm indication signal (AIS) is detected at the input of the demultiplexer, the promptmaintenance alarm indication associated with loss of frame alignment should be inhibit
25、ed, while the rest of theconsequent actions are in accordance with those associated in Table 2/G.747 with the fault condition.10.2.1 Alarm indication to the remote multiplex equipment should be generated by changing bit 1 of Set II (seeTable 1/G.747) from the state 0 to the state 1.10.2.2 AIS should
26、 be applied to the following as specified in Table 2/G.747.- all three 2048 kbit/s tributary outputs from the demultiplexer;- 6312 kbit/s output of the multiplexer;- the time slots of the 6312 kbit/s signal at the output of the multiplexer, corresponding to the relevant2048 kbit/s tributary.6 Fascic
27、le III.4 - Rec. G.747TABLE 2/G.747Fault conditions and consequent actionsConsequent actions (see 10.2)AIS appliedEquipmentpartFault condition(see 10.1)PromptmaintenancealarmindicationgeneratedAlarmindication tothe remotemultiplexequipmentgeneratedTo all thetributariesTo thecompositesignalTo the rele
28、vanttime slotsof thecompositesignalMultiplexeranddemultiplexerFailureof power supplyYes Yes(if practicable)Yes(if practicable)MultiplexeronlyLoss of incoming signalon a tributaryYes YesLoss of incoming signalat 6312 kbit/sYes Yes YesDemultiplexerLoss of frame alignment Yes Yes YesonlyAlarm indicatio
29、nreceived fromthe remote multiplexequipmentNote - A Yes in the table signifies that a certain action should be taken as a consequence of the relevant fault condition. An open spacein the table signifies that the relevant action should not be taken as a consequence of the relevant fault condition, if this condition isthe only one present. If more than one fault condition is simultaneously present the relevant action should be taken if, for at least oneof the conditions, a Yes is defined in relation to this action.
