1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/ further amended)1 GeneralThe second order digital multiplex equipment using positive justification described below, is intended for useon digital paths between countries using 1544 kbit/s
2、 primary multiplex equipments.2 Bit rateThe nominal bit rate should be 6312 kbit/s.The tolerance on that rate should be 30 parts per million (ppm).3 Frame structureTable 1/G.743 gives:- the tributary bit rate and the number of tributaries;- the number of bits per frame;- the bit numbering scheme;- t
3、he bit assignment;- the distributed frame and multiframe alignment signals.4 Loss and recovery of frame and multiframe alignment and consequent actionThe frame alignment recovery time should not exceed 16 ms. The signal to be applied to the tributaries duringthe out-of-frame-alignment time should be
4、 studied.Once frame alignment is established, multiframe alignment should be recovered in less than 420 microseconds.5 Multiplexing methodCyclic bit interleaving in the tributary numbering order and positive justification is recommended.The justification control signal should be distributed and use
5、the Cjn-bits (n = 1, 2, 3, see Table 1/G.743).Positive justification should be indicated by the signal 111, no justification by the signal 000. Majority decisionis recommended.Table 1/G.743 gives the maximum justification rate per tributary and the nominal justification ratio.6 Jitter6.1 Specificati
6、ons at the input portsThe digital signal presented at the input ports shall be as defined in Recommendation G.703 modified by the2 Fascicle III.4 - Rec. G.743transmission characteristic of the interconnecting cable. The input ports shall be able to tolerate a digital signal withthese electrical char
7、acteristics but modified by sinusoidal jitter up to the limits specified by the amplitude frequencyrelationship in Figure 1/G.743. The equivalent binary content of the signal, with jitter modulation, applied to the inputsshall be a pseudo-random bit sequence of length 215- 1.Note - The signal with j
8、itter modulation applied to the demultiplexer input shall contain the bits necessary forframing and justification in addition to information bits.TABLE 1/G.7436312-kbit/s multiplexing frame structureTributary bit rate (kbit/s) 1544Number of tributaries 4Frame structure (see Notes 1 and 2) Bit number
9、Bit for multiframe alignment signal (Mj) (see Note 1)Bits from tributaries1st bit for justification control signal (Cj1)Bits from tributaries1st bit for frame alignment signal (F0) (see Note 3)Bits from tributaries2nd bit for justification control signal (Cj2)Bits from tributaries3rd bit for justifi
10、cation control signal (Cj3)Bits from tributaries2nd bit for frame alignment signal (F1) (see Note 3)Bits from tributaries (see Note 4)Set I12 to 49Set II12 to 49Set III12 to 49Set IV12 to 49Set V12 to 49Set VI12 to 49Frame lengthMultiframe lengthBits per tributary per multiframe (including justifica
11、tion)Maximum justification rate per tributaryNominal justification ratio294 bits1176 bits288 bits5367 bit/s0.334Note 1 - This frame is repeated 4 times to form a multiframe with designated j = 1, 2, 3 , 4. The multiframealignment signal is a 011x-pattern. x may be used as an alarm service digit.Note
12、 2 - The bits from the second and fourth tributaries are inverted logically before multiplexing with thebits from the first and third tributaries.Note 3 - The frame alignment is F0= 0 and F1= 1.Note 4 - The bit available for the justification of tributary j is the first time slot of tributary j foll
13、owing F1inthe jth frame.Fascicle III.4 - Rec. G.743 3Input A1(UI) A2(UI) f1(Hz) f2 (Hz) f3(kHz) f4(kHz)1544 kbit/s 2 0.05 10 200 8 406312 kbit/s(provisional)8 0.05 10 200 32 160UI Unit intervalFIGURE 1/G.743Lower limit of maximum tolerable input jitter6.2 Multiplex signal output jitterThe jitter at
14、the 6312 kbit/s output of the multiplexer should not exceed 0.01 UI rms.6.3 Demultiplexer output jitter with no multiplexer or demultiplexer input jitterWith no jitter at the input to the multiplexer and demultiplexer, the jitter at the demultiplexer output should notexceed 1/3 unit intervals peak-t
15、o-peak.6.4 Demultiplexer jitter transfer characteristicThe gain of the jitter transfer characteristic should not exceed the limits given in Figure 2/G.743.Note - The frequency f0should be as low as possible taking into account the limitations of measuring equipment.FIGURE 2/G.743Demultiplexer transf
16、er characteristic4 Fascicle III.4 - Rec. G.7437 Digital interfacesThe digital interfaces at 1544 kbit/s and 6312 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 multiplexer timing signal from anexter
17、nal source as well as from an internal source.9 Service digitsThe service digits are reserved for national use.10 Fault conditions and consequent actions10.1 Fault conditionsThe digital multiplex equipment should detect the following fault conditions.10.1.1 Failure of power supply.10.1.2 Loss of fra
18、me alignment at the demultiplexer.It may also be equipped to detect the following fault conditions.10.1.3 Loss or degradation of incoming 1544 kbit/s signal.10.1.4 Loss or degradation of incoming 6312 kbit/s signal.10.1.5 Failure of the multiplex or demultiplex as evidenced by incorrect multiplexing
19、 or demultiplexing action.10.1.6 Failure of standby (if the multiplex is so equipped).10.2 Consequent actionsOn the detection of a fault condition, the following appropriate actions should be taken:10.2.1 For a multiplex equipped with automatic changeover, the consequent actions are specified in Tab
20、le 2/G.743.For a multiplex so equipped, a switch to a standby is performed in the event of a failure of the multiplex equipment inservice. A maintenance alarm is generated if a switch takes place, or if the standby fails. A prompt maintenance alarm isgenerated if an incoming signal fails, or if serv
21、ice is lost due to inability to complete automatic changeover to thestandby.10.2.2 For a multiplex not equipped with automatic changeover, a prompt maintenance alarm is generated in responseto any fault condition detected. Such multiplexers will normally be equipped to detect power failure and loss
22、ordegradation of incoming signal at the demultiplexer.10.2.3 The provision of an Alarm Indication Signal (AIS) to the 1544 kbit/s tributary outputs from the demultiplexeris under study. An AIS, suitable for use without special detectors at the primary PCM multiplex might be provided on anoptional ba
23、sis.Fascicle III.4 - Rec. G.743 5TABLE 2/G.743Fault conditions and consequent actions for a multiplex equipped with automatic changeoverConsequent actions (see 10.2.1)Equipment part Fault condition(see 10.1)Promptmaintenancealarm indicationgeneratedDeferredmaintenancealarm indicationgeneratedAlarm i
24、ndicationto the remotemultiplexequipmentgenerated(if so equipped)AutomaticchangeoveractuatedMultiplexerdemultiplexerFailureof power supplyNo Yes YesMultiplexer only Loss or degradationof incoming signalon a tributaryYes NoDemultiplexerLoss or degradationof incoming signalat 6312 kbit/sYes Yes Noonly
25、Alarm indicationreceived from theremote multiplexequipment(if so equipped)YesNote - A Yes in the table signifies that a certain action should be taken as a consequence of the relevant fault condition. An openspace in the table signifies that 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 to this action.Fascicle III.4 - Rec. G.743
