1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/ amended at Geneva, 1980 and at Melbourne, 1988)1 General characteristics1.1 Fundamental characteristicsThe encoding law used is the A-law as specified in Recommendation G.711. The samplin
2、g rate, load capacityand the code are also specified in that Recommendation.The number of quantized values is 256.Note - The inversion of bits 2, 4, 6 and 8 is covered by the encoding law and is applicable only to voice-channeltime slots.1.2 Bit rateThe nominal bit rate is 8448 kbit/s. The tolerance
3、 on this rate is 30 parts per million (ppm).1.3 Timing signalIt should be possible to derive the transmitting timing signal of a PCM multiplex equipment from an internalsource, from the incoming digital signal and also from an external source.Note - Further study is required on the effect of jitter
4、of the incoming signal on the timing signal, and on themeasures to be taken in case of loss of the incoming signal or the external source.2 Frame structureRefer to 3.4.1 and 3.4.2 of Recommendation G.704 for frame structure and use of derived channel time slots.3 Loss and recovery of frame alignment
5、Loss of frame alignment should be assumed to have taken place when four consecutive frame alignment signalshave been incorrectly received in their predicted positions.When frame alignment is assumed to be lost, the frame alignment device should decide that such alignment haseffectively been recovere
6、d when it detects the presence of three consecutive frame alignment signals.The frame alignment device having detected the appearance of a single correct frame alignment signal, shouldbegin a new search for the frame alignment signal when it detects the absence of the frame alignment signal in one o
7、f thetwo following frames.4 Fault conditions and consequent actions4.1 Fault conditionsThe PCM multiplex equipment should detect the following fault conditions.4.1.1 Failure of power supply.2 Fascicle III.4 - Rec. G.7444.1.2 Failure of codec (except when using single-channel codecs)As a minimum requ
8、irement, this fault condition should be recognized when, for at least one signal level in therange -21 to -6 dBm0, the signal-to-quantizing noise ratio performance of the local codec is 18 dB or more below thelevel recommended in Recommendation G.712.4.1.3 Loss of incoming signal at the 64 kbit/s in
9、put port (time slots 67 to 70)Note 1 - The detection of this fault condition is not mandatory when channel associated signalling is used andthe signalling multiplex is situated within a few metres of the PCM multiplex equipment.Note 2 - The detection of this fault condition is not mandatory when con
10、tradirectional interfaces are used.4.1.4 Loss of the incoming signal at 8448 kbit/s.Note 1 - The detection of this fault condition is required only when it does not result in an indication of loss offrame alignment.Note 2 - Where separate circuits are used for the digital signal and the timing signa
11、l, then loss of either or bothshould constitute loss of the incoming signal.4.1.5 Loss of frame alignment.4.1.6 Excessive bit error ratio detected by monitoring the frame alignment signal.4.1.6.1 With a random bit error of 10-4, the probability of activating the indication of fault condition within
12、a fewseconds should be less than 10-6.With a random bit error of 10-3, the probability of activating the indication of fault condition within a fewseconds should be higher than 0.95.4.1.6.2 With a random bit error ratio of 10-3, the probability of deactivating the indication of fault condition withi
13、n afew seconds should be almost 0.With a random bit error of 10-4, the probability of deactivating the indication of fault condition within a fewseconds should be higher than 0.95.Note - The activating and the deactivating period specified as “a few seconds“ is intended to be in the order of4 to 5 s
14、econds.4.1.7 Alarm indication received from the remote end (see 4.2.3 below).4.2 Consequent actionsFurther to the detection of a fault condition, appropriate actions should be taken as specified in Table 1/G.744.The consequent actions are as follows:4.2.1 Service alarm indication generated to signif
15、y that the service provided by the PCM multiplex is no longeravailable. This indication should be forwarded at least to the switching and/or signalling multiplex equipment dependingupon the arrangements provided. The indication should be given as soon as possible and not later than 2 ms afterdetecti
16、on of the relevant fault condition.This specification, taking into account the specification given in 3 above, is equivalent to recommending thatthe average time to detect a loss of frame alignment or a loss of the incoming 8448-kbit/s signal and to give the relevantindication should not be greater
17、than 3 ms.When using common channel signalling, the indication should be forwarded to the switching equipment bymeans of a separate interface on the PCM multiplex equipment.4.2.2 Prompt maintenance alarm indication generated to signify that performance is below acceptable standards andmaintenance at
18、tention is required locally. When the Alarm Indication Signal (AIS) (see General Note below to 4.2) isFascicle III.4 - Rec. G.744 3detected the prompt maintenance alarm indication, associated with loss of frame alignment (see 4.1.5 above) andexcessive error rate (see 4.1.6 above), should be inhibite
19、d, while the rest of the consequent actions are in accordancewith those associated in Table 1/G.744 with the two fault conditions.Note - The location and provision of any visual and/or audible alarms activated by the alarm indications givenin 4.2.1 and 4.2.2, is left to the discretion of each Admini
20、stration.4.2.3 Alarm indication to the remote end generated by changing bit 7 of channel time slot 66 from the state 0 to thestate 1. This should be effected as soon as possible.4.2.4 Transmission suppressed at the analogue outputs.4.2.5 AIS applied to time slots 67 to 70 of the 64 kbit/s outputs wh
21、en not used for speech (see General Note belowto 4.2). This action should be taken as soon as possible and not later than 2 ms after the detection of the faultcondition.4.2.6 AIS applied to time slots 67 to 70 of the output 8448 kbit/s composite signal when these are not used forspeech (if supervisi
22、on of incoming 64 kbit/s signal is provided).General Note to 4.2 - The equivalent binary content of the AIS is a continuous stream of binary 1s.The strategy for detecting the presence of the AIS should be such that the AIS is detectable, even in thepresence of an error ratio 1 10-3. However, a signa
23、l with all bits except the frame alignment in the 1s state, should notbe mistaken for an AIS.Note - All timing requirements quoted apply equally to restoration, subsequent to the fault condition clearing.4 Fascicle III.4 - Rec. G.744TABLE 1/G.744Fault conditions and consequent actions for the PCM mu
24、ltiplex equipmentConsequent actions (see 4.2)EquipmentpartFault condition(see 4.1)ServicealarmindicationgeneratedPromptmaintenancealarmindicationgeneratedAlarmindicationto theremote endgeneratedTrans-missionsuppressedat theanalogueoutputsAISappliedto 64-kbit/soutputs(time slots67 to 70)AIS appliedto
25、 time slots67 to 70of the8448 kbit/scompositesignalMultiplexerandFailureof power supplyYes Yes Yes, ifpracticableYes, ifpracticableYes, ifpracticableYes, ifpracticabledemultiplexerFailure of codec Yes Yes Yes YesMultiplexeronlyLoss of incoming signalat 64-kbit/s inputs timeslots 67 to 70(see notes u
26、nder 4.1.3)Yes YesLoss of incomingsignal at 8448 kbit/sYes Yes Yes Yes YesLoss of frame alignment Yes Yes Yes Yes YesDemultiplexerError rate 1 in 10-3for the alignment signalYes Yes Yes Yes YesonlyAlarm indication receivedfrom the remote end(bit 7 of time slot 66)YesNote - A Yes in the table signifi
27、es 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
28、simultaneously present the relevant action should be taken if, for at least oneof the conditions, a Yes is defined in relation to this action.5 Signalling5.1 Signalling arrangementRefer to 3.4.3 of Recommendation G.704. Channel time-slots 67 to 70 may be used to provide an interface at64 kbit/s whic
29、h shall be suitable for use with either common channel or channel-associated signalling or other servicesas required.5.2 Loss and recovery of multiframe alignment in case of channel associated signallingFor multiframe alignment each 64 kbit/s channel should be treated separately. For each channel, m
30、ultiframeFascicle III.4 - Rec. G.744 5alignment should be assumed to have been lost when two consecutive multiframe alignment signals have been receivedwith an error.Multiframe alignment should be assumed to have been recovered as soon as the first correct multiframe signalis detected.Note - To avoi
31、d a condition of spurious multiframe alignment, the following procedure may be used, in additionto the above:- Multiframe alignment should be assumed to have been lost when, for a period of one or two multiframes,all the bits in the relevant channel time slots 67, 68, 69 or 70 are at the state 0.- M
32、ultiframe alignment should be assumed to have been recovered, only when at least one bit in the state 1is present in the relevant time slots 67, 68, 69 or 70 preceding the multiframe alignment signal firstdetected.5.3 Fault conditions and consequent actions in case of channel associated signallingTh
33、e fault conditions and consequent actions for each 64 kbit/s signalling channel and for each signallingmultiplex equipment are the same as recommended in Recommendation G.732, 5.3.6 InterfacesThe analogue interfaces should be in accordance with Recommendations G.712, G.713 and G.714. The digitalinte
34、rfaces at 8448 kbit/s should be in accordance with Recommendation G.703. The digital interfaces at 64 kbit/s shouldbe of either the codirectional or the contradirectional type specified in Recommendation G.703. The specifications for64 kbit/s interfaces are not mandatory for channel associated signa
35、lling.7 Jitter7.1 Multiplex signal output jitter at 8448 kbit/s outputIn the case where the transmitting timing signal is derived from an internal oscillator, the peak-to-peak jitter atthe 8448 kbit/s output should not exceed 0.05 UI when it is measured within the frequency range from f1= 20 Hz tof4
36、 = 400 kHz.7.2 Jitter at 64 kbit/s output (for interfaces according to Rec. G.703)7.2.1 In the case where the incoming 8448 kbit/s signal has no jitter, the peak-to-peak jitter at the 64 kbit/s outputshould not exceed 0.025 UI when it is measured within the frequency range from f1= 20 Hz to f4= 10 k
37、Hz. Theequivalent binary content of the test signal applied to the 8448 kbit/s input shall be a pseudo-random bit sequence oflength 215- 1 as specified in Recommendation O.151.Note - In order to carry out this measurement without invoking AIS at the 64 kbit/s output, it will normally benecessary to include a frame alignment signal in the test signal.7.2.2 The jitter transfer function between the 8448 kbit/s input and the 64 kbit/s output is under study.Fascicle III.4 - Rec. G.744
