1、INTERNATIONAL TELECOMMUNICATION UNION)45 4 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!, !30%#43 / i = 1, 2, 3, 4, 5) (seeNote 6 to Table 1/G.755).Positive justification should be indicated by the justification control signal 11111 and no justification by thesignal 00000. Majority decision is
2、recommended.Table 1/G.755 gives the maximum justification rate per tributary and the nominal justification ratio.6 Jitter6.1 Demultiplexer triburaty jitter transfer characteristicThe demultiplexer 44 736 kbit/s tributary jitter transfer characteristic should meet the gain/frequency limits given inFi
3、gure 1/G.755. The equivalent binary content of the test signal used should result in a tributary output signal of 1000.2 Fascicle III.4 - Rec. G.755TABLE 1/G.755139 264 kbit/s multiplexing frame structureNote 1 - Cji(j = 1, 2, 3; i = 1, 2, 3, 4, 5) indicates the ith justification control bit of the
4、jth tributary.Note 2 - See 10.2.1.Note 3 - 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 bits in the justifiable time-slots in
5、 the preceding frame is even.Note 4 - It is recognized that existing multiplex equipment installed prior to adoption of thisRecommendation does not insert the parity bit.Note 5 - The implementation and the use of this parity bit procedure are for further study.Note 6 - These bits should be set to 1
6、when not used.Nominal tributary bit rate (kbit/s) 44 736Number of tributaries 3Frame structure Bit numberFrame alignment signal (111110100000)Bits from tributariesJustification control bits Cj1(Note 1)Bits from tributariesJustification control bits Cj2 (Note 1)Bits from tributariesJustification cont
7、rol bits Cj3(Note 1)Alarm indication to the remote multiplex equipment (Note 2)Parity bit (Notes 3, 4 and 5)Bits reserved for future use (Note 6)Bits from tributariesJustification control bits Cj4 (Note 1)Bits from tributariesJustification control bits Cj5(Note 1)Bits from tributaries available for
8、justificationBits from tributariesSet I1 to 1213 to 159Set II1 to 34 to 159Set III1 to 34 to 159Set IV1 to 3456 to 910 to 159Set V1 to 34 to 159Set VI1 to 34 to 67 to 159Frame lengthBits per tributary in a frameMaximum justification rate per tributaryNominal justification ratio954 bits307 bits146 kb
9、it/s0.545Fascicle III.4 - Rec. G.755 3Note 1 - This characteristic is usually measured between the high speed and low speed interfaces of thedemultiplexer and the measurements are taken in unit intervals. It is then necessary to introduce a correction factor toaccount for the difference in the size
10、of unit intervals.Note 2 - In addition, the need to specify a muldex jitter transfer characteristic is for further study.Note 3 - It is recognized that the existing multiplex equipment designed prior to the adoption of thisRecommendation might need tributary test signals incorporating the 44 736 kbi
11、t/s frame structure defined inRecommendation G.572.Note - The frequency f0should be as low as possible, taking into account thelimitations of measuring equipment In any case f0should be no greater than 10 Hz. Theselective measurement method should be used.FIGURE 1/G.755Demultiplexer tributary jitter
12、 transfer characteristic6.2 Output jitter6.2.1 Tributary output jitterWith no jitter applied to the input ports of the multiplexer and with the multiplexer directly connected to thedemultiplexer, the peak-to-peak jitter at the tributary output port should not exceed 0.3 UI when measured over a onemi
13、nute interval within the frequency range from f1= 10 Hz to f4= 400 Hz.When measured with an instrument incorporating a bandpass filter having a lower cutoff frequency off3 = 60 kHz, a roll-off of 20 dB/decade and an upper limit of f4= 400 kHz, the peak-to-peak output jitter should notexceed 0.05 UI
14、when it is measured over a one minute interval.6.2.2 Multiplexer output jitterThe peak-to-peak jitter at the 139 264 kbit/s output port should not exceed 0.05 UI when it is measured over aone minute interval within the frequency range from 200 Hz to 3500 kHz.6.3 Input jitter6.3.1 Tributary input jit
15、terThe 44 736 kbit/s input port should be capable of accommodating levels of input jitter up to the limits given inFigure 2/G.755.Note - Current Recommendation G.703 does not refer to the jitter tolerated at the digital distribution frame at44 736 kbit/s nor at the input port of equipment connected
16、to this distribution frame.4 Fascicle III.4 - Rec. G.755Peak-to-peak sinusoidaljitter amplitudeFrequencyA1 (UI) A2 (UI) f1 (Hz) f2(Hz) f3(kHz) f4 (kHz)5.0 0.1 10 2.3 60 400FIGURE 2/G.755Lower limit of maximum tolerable sinusoidal input jitterat 44 736 kbit/s6.3.2 Demultiplexer input jitterThe 139 26
17、4 kbit/s input port should be capable of accommodating levels of input jitter up to the limits given inRecommendation G.823.Note - 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
18、the 44 736 kbit/s level.7 Digital interfacesThe digital interfaces at 44 736 kbit/s and 139 264 kbit/s should be in accordance with Recommendation G.703.8 Timing signalIf it is economically feasible, it may be desirable to be able to derive the multiplexing timing signal from anexternal source as we
19、ll as from an internal source.9 Service digitsSix bits per frame are available for service functions (see Table 1/G.755): bit 4 of Set IV is used to transmit analarm indication to the remote multiplex equipment when specific fault conditions are detected in the multiplexequipment when specific fault
20、 conditions are detected in the multiplex equipment (see 10 below); bit 5 of Set IV maybe used for a parity check; bits 6 to 9 of Set IV are reserved for further use.Fascicle III.4 - Rec. G.755 510 Fault conditions and consequent actions10.1 Fault conditions10.1.1 The digital multiplex equipment sho
21、uld detect the following fault conditions:1) failure of power supply;2) loss of an incoming 44 736 kbit/s tributary signal at a multiplexer input port;3) loss of an incoming 139 264 kbit/s multiplex signal at a demultiplexer input port;Note - The detection of this fault condition is required only wh
22、en it does not result in an indication of loss offrame alignment.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 demultiple
23、xer input port.Note 1 - The equivalent binary content of the AIS at 139 264 kbit/s should be a continuous stream of binary 1s(marks) as recommended in Recommendation M.20.Note 2 - The strategy for detecting the presence of the AIS should be such that the AIS is detectable even in thepresence of an e
24、rror 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 139 264 kbit/s signal for the purpose of end-to-end errorperformance monitoring of the 139 264 kbit/s d
25、igital block, as well as the procedure for detecting such degradation arefor further study.10.2 Consequent actionsFurther to the detection of a fault condition, the appropriate actions should be taken as specified inTable 2/G.755.Note 1 - The concept and definition of prompt maintenance alarm indica
26、tion 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 inhibited, while the rest of theconsequent actions are in accordance with those
27、 associated in Table 2/G.755 with the fault condition.10.2.1 Alarm indication to the remote multiplex equipment should be generated by changing bit 4 of Set IV (seeTable 1/G.755) from the state 0 to the state 1.10.2.2 AIS should be applied to the following as specified in Table 2/G.755:- all three 4
28、4 736 kbit/s tributary outputs from the demultiplexer;- 139 264 kbit/s output of the multiplexer;- the time slots of the 139 264 kbit/s signal at the output of the multiplexer, corresponding to the relevant44 736 kbit/s tributary.Note - The equivalent binary content of the AIS at 44 736 kbit/s is a
29、signal with a valid frame alignment signal,parity and justification control bits as defined in Table 2/G.752, with the tributary bits being set to a 1010 . sequence,starting with a binary 1 after each frame alignment, multi-frame alignment and justification control bit, and with alljustification con
30、trol bits being set to binary 0.6 Fascicle III.4 - Rec. G.755TABLE 2/G.755Fault conditions and consequent actionsNote - 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 sh
31、ould 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.Consequent a
32、ctions (see 10.2)AIS appliedEquipmentpartFault condition(see 10.1)PromptmaintenancealarmindicationgeneratedAlarmindication tothe remotemultiplexequipmentgeneratedTo all thetributariesTo thecompositesignalTo the relevanttime slotsof thecompositesignalMultiplexeranddemultiplexerFailureof power supplyYes Yes, ifpracticableYes, ifpracticableMultiplexeronlyLoss of incoming signalon a tributaryYes YesLoss of incoming signalat 139 264 kbit/sYes Yes YesDemultiplexerLoss of frame alignment Yes Yes YesonlyAlarm indicationreceived fromthe remote multiplexequipment
