1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/- unidirectional synchronous 384 kbit/s access (Figure l b/G.737).The 384 kbit/s channel is based on the allocation of 6 x 64 kbit/s time slots, e.g. for setting up sound-programme circuit
2、s according to Recommendations J.41 and J.42. Because these circuits are specified as unidirectionalthe equipment for insertion/extraction has to be separated as shown in Figure l b/G.737.FIGURE 1/G.737External access equipment for 64 and 384 kbit/s channels2 Fascicle III.4 - Rec. G.7371 General cha
3、racteristics1.1 Bit rateThe nominal bit rate is 2048 kbit/s. The tolerance on this rate is 50 parts per million (ppm).1.2 Types of external accessa) Bidirectional synchronous insertion/extraction of 64 kbit/s data channels (see Figure l a/G.737).Note 1 - The timing signal for the insertion side shou
4、ld be derived from the 2048 kbit/s incoming signal atthe insertion side (I0): the timing signal for the extraction side should be derived from the 2048 kbit/sincoming signal at the extraction side (E1).Note 2 - The provision of a timing signal output, available for the purpose of synchronizing other
5、equipments, is an option that might be required depending upon national synchronization arrangements.Note 3 - Further study is required on the possible need for an internal clock.b) Unidirectional synchronous insertion and extraction of a digital sound-programme signal into/out of a384 kbit/s channe
6、l (see Figure l b/G.737).Note - The synchronous insertion equipment for 384 kbit/s signals requires the internal regeneration of atiming signal synchronized by the 2048 kbit/s input signal I0. This timing signal output of the synchronousinsertion equipment is used for synchronizing the sampling freq
7、uency of the analogue/digital converter.2 Frame structure and use of derived channel time slots2.1 Frame structure of the 2048 kbit/s signalRefer to 2.3 of Recommendation G.704. Bit 1 of the frame should be used in accordance with 2.3.3 ofRecommendation G.704, i.e. for a CRC check bit procedure.2.2
8、Use of derived channel time slotsTime slots not accessed flow transparently through the equipment.Note - Further study is required as to whether the binary content of time slots used at the access points shouldbe replaced, after extraction from the composite signal, by the AIS.2.2.1 64 kbit/s access
9、The number of accessible channel time slots should be at least four and the equipment shall allow access to anyof channel time slots 1 to 15 and 17 to 31.Note - Equipment exists which provides access to at least four channel time slots in the following order ofpriority: 6 - 22 - 14 - 30 - 2 - 18 - 1
10、0 - 26 - 4 - 20 - 12 - 28 - 8 - 24 - 5 - 21 - 13 - 29 - 1 - 17 - 9 - 25 - 3 - 19 - 11 - 27 - 7 -23 - 15 - 31.2.2.2 384 kbit/s accessThe time slot allocation for digital channels with a bit rate at 384 kbit/s is given in Table 1/G.737.Fascicle III.4 - Rec. G.737 3TABLE 1/G.737384 kbit/s channels (Not
11、e 1)Digital sound-programme accessABCDEpoints1-2-317-18-194-5-620-21-227-8-923-24-2510-11-1226-27-2813-14-1529-30-31I3, T, E3Figure 1b/G.735Note 1 - The five possible 384 kbit/s channels in a 2048 kbit/s stream are numbered A to E. Preferably the channel pairs A-B and C-Dshould be used for stereopho
12、nic transmission.Note 2 - If the channel time slot 16 which is assigned to signalling as covered in 5 is not needed for signalling, it may be used forpurposes other than a voice channel encoded within the PCM multiplex equipment.3 Frame alignment and CRC procedures both at insertion (I0) and extract
13、ion (E1) sidesAn illustration of the procedure is given in Figure 2/G.706.3.1 Loss of frame alignmentRefer to 4.1.1 of Recommendation G.706.3.2 Recovery of frame alignmentRefer to 4.1.2 of Recommendation G.706.3.3 CRC multiframe alignment in TSORefer to 4.2 of Recommendation G.706.3.4 CRC bit monito
14、ringRefer to 4.3 of Recommendation G.706.4 Fault conditions and consequent actions4.1 Fault conditionsThe equipment should detect the following fault conditions:4.1.1 Failure of power supply.4.1.2 Loss of incoming signal at I2or I3.Note - This detection is not mandatory when contradirectional interf
15、aces are used.4.1.3 Loss of the incoming signal at 2048 kbit/s both at insertion (I0) and extraction (E1) sides.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
16、 signal and the timing signal, the loss of either or bothshould constitute loss of the incoming signal.4.1.4 Loss of frame alignment both at insertion (I0) and extraction (E1) sides.4 Fascicle III.4 - Rec. G.7374.1.5 Excessive bit error ratio detected by monitoring the frame alignment signal at both
17、 the insertion (I0) andextraction (E1) sides.Note - The detection of this fault condition at insertion side (I0) depends on the type of application of thisequipment in a network and therefore is not mandatory.4.1.5.1 With a random bit error ratio of 10-4, the probability of activating the indication
18、 of fault condition within afew seconds should be less than 10-6.With a random bit error ratio of 10-3, the probability of activating the indication of fault condition within afew seconds should be higher than 0.95.4.1.5.2 With a random bit error ratio of 10-3, the probability of deactivating the in
19、dication of fault condition within afew seconds should be almost 0.With a random bit error ratio of 10-4, the probability of deactivating the indication of fault condition within afew seconds should be higher than 0.95.Note - The activating and the deactivating period specified as “a few seconds“ is
20、 intended to be in the order of4 to 5 seconds.4.2 Consequent actionsFurther to the detection of a fault condition, appropriate actions should be taken as specified in Table 2/G.737.The consequent actions are as follows:4.2.1 Prompt maintenance alarm indication generated to signify that performance i
21、s below acceptable standards andmaintenance attention is required locally. When the AIS at the 2048 kbit/s inputs (I0, E1) is detected (see General Notesbelow to 4.2), the prompt maintenance alarm indication associated with loss of frame alignment (see 4.1.4) andexcessive error ratio (see 4.1.5) sho
22、uld be inhibited, while the rest of the consequent actions are in accordance withthose associated in Table 2/G.737 with the two fault conditions.Note - The location and provision of any visual and/or audible alarm activated by the alarm indications given in 4.2.1 is left to the discretion of each Ad
23、ministration.4.2.2 AIS applied to E2or E3outputs (see General Notes below to 4.2). This action should be taken as soon aspossible and not later than 2 ms after the detection of the fault condition.4.2.3 AIS applied to relevant time slots in the composite 2048 kbit/s output signal at insertion side (
24、I1) if supervisionof the incoming I2and I3signal is provided.4.2.4 Inhibition of I2or I3digital information insertion.4.2.5 Both 2048 kbit/s signals are bypassed.Note - The provision of this consequent action depends on the type of application of this equipment in anetwork and therefore is not manda
25、tory.4.2.6 AIS applied to the 2048 kbit/s output, extraction side (E0).Note - The provision of this consequent action depends on the type of application of this equipment in anetwork and therefore is not mandatory.Fascicle III.4 - Rec. G.737 54.2.7 AIS applied to the 2048 kbit/s output, insertion si
26、de (I1).Note - The provision of this consequent action depends on the type of this equipment in a network and thereforeis not mandatory.General Note to 4.2Note 1 - The equivalent binary content of the alarm indication signal (AIS) is a continuous stream of binary 1s.The strategy for detecting the pr
27、esence of the AIS should be such that with a high probability the AIS is detectable evenin the presence of random errors having a mean error ratio 1 10-3. Nevertheless, a signal in which all the binaryelements, with the exception of the frame alignment signal, are in the state 1, should not be taken
28、 as an AIS.Note 2 - All timing requirements quoted apply equally to restoration, subsequent to the fault condition clearing.5 InterfacesThe digital interfaces at 2048 kbit/s should be in accordance with Recommendation G.703.The digital interfaces at 64 kbit/s should be either of the codirectional or
29、 the contradirectional type specified inRecommendation G.703.The need to define a digital interface operating at 384 kbit/s is under study.Note 1 - It should be noted that according to the principle of minimizing the number of different types ofinterfaces, the information rate of 384 kbit/s will be
30、offered to customers at the user/network interface level using the2048 kbit/s interface as defined in Recommendations I.431 and G.703.Note 2 - In the case of the 64 kbit/s codirectional interface, the design of the input ports should take account ofthe need to provide octet alignment, to allow contr
31、olled slips when the tributary timing and that of the multiplexer timingsource are plesiochronous, and to absorb jitter and wander up to the limits given in Recommendation G.823.6 Fascicle III.4 - Rec. G.737TABLE 2/G.737Fault conditions and consequent actions for the external access equipmentConsequ
32、ent actions (see 4.2)Fault conditions (see 4.1)PromptmaintenancealarmsindicationgeneratedAIS applied to E2or E3outputsInhibition ofdigitalinformationinsertionI2, I3AIS applied to therelevant time slot of the2048 kbit/s compositesignal at insertion side(I1)Both 2048 kbit/ssignal are bypassed(see Note
33、 under 4.2.5)AIS applied to the2048 kbit/s output,extraction side (E0)(see Note under 4.2.6)AIS applied to the2048 kbit/s output,insertion side (I1)(see Note under 4.2.7)Failure of power supply Yes Yes Yes(if practicable)Yes(if practicable)Loss of incoming signal at I2or I3 inputs (see Note under 4.
34、1.2)Yes YesLoss ofincomingExtr.s. (E1)Yes Yes Yessignal at2048 kbit/sIns.s. (I0) Yes Yes YesLoss of framealignment (seeExtr.s. (E1)Yes(see 4.2.1)Yes YesNote 2 of Rec.G.706, 4.2)Ins.s. (I0)Yes(see 4.2.1)Yes YesError ratio1 10-3on theframeExtr.s. (E1) Yes(see 4.2.1)Yes Yesalignmentsignal (seeNote unde
35、r 4.1.5)Ins.s. (I0)Yes(see 4.2.1)Yes YesNote - A Yes in the table signifies that an action should be taken as a consequence of the relevant fault condition. An open space in the table signifies that the relevant actionshould not be taken as a consequence of the relevant fault condition, if this cond
36、ition is the only one present. If more than one fault condition is simultaneously present, therelevant action should be taken if, for at least one of the conditions, a Yes is defined in relation to this action.Fascicle III.4 - Rec. G.737 76 Jitter6.1 Jitter at 2048 kbit/s outputWhen there is no jitt
37、er on the 2048 kbit/s inputs (I0, E1) the peak-to-peak jitter at the 2048 kbit/s outputs (I1, E0)should not exceed 0.10 UI when it is measured within the frequency range from f1= 20 Hz to f4= 100 kHz. Theequivalent binary content of the test signal applied at the 2048 kbit/s input shall be a pseudo-
38、random bit sequence oflength 215- 1 as specified in Recommendation O.151. See Figure 2/G.823.Note - It may be necessary to include a frame alignment signal in the test signal to enable the measurement to becarried out.6.2 Jitter at E2and E3outputs6.2.1 The jitter at the E2(64 kbit/s) output when the
39、re is no jitter at the 2048 kbit/s input (E1) should not exceed0.025 UI when measured within the frequency range from f1= 20 Hz to f4= 10 kHz. The equivalent binary content ofthe test signal applied at the 2048 kbit/s input shall be a pseudo-random bit sequence of length 215- 1 as specified inRecomm
40、endation 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.6.2.2 Since the physical and electrical characteristics of a 384 kbit/s interface are identical to those of t
41、he 2048 kbit/sinterface, the jitter at the E3(synchronous 384 kbit/s) output when there is no jitter at the 2048 kbit/s input (E1) isaccording to 6.1 above.6.3 Jitter transfer functions6.3.1 The jitter transfer function between the 2048 kbit/s input (I0, E1) and the output (I1, E0) should not exceed
42、 thegain/frequency limits given in Figure 2/G.737.Some Administrations require that equipment be fitted with jitter reducers. In this case, the jitter transferfunction should not exceed the gain/frequency limits given in Figure 3/G.737.Note 1 - The 2048 kHz signal shall be modulated with sinusoidal
43、jitter. The equivalent binary content of the testsignal shall be 1000.Note 2 - It may be necessary to include a frame alignment signal in the test signal to enable the measurement tobe carried out.6.3.2 The jitter transfer function between the 2048 kbit/s input (E1) and the E2(64 kbit/s) output shou
44、ld not exceed-29.6 dB when measured over the frequency range f0to 10 kHz. The frequency f0should be less than 20 Hz and as lowas possible (e.g. 10 Hz), taking into account the limitations of measuring equipment.Note 1 - The 2048 kbit/s test signal shall be modulated by sinusoidal jitter. The equival
45、ent binary content of thetest signal shall be 1000.Note 2 - 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.Note 3 - The jitter reduction of 1/32 due to demultiplexing is equivale
46、nt to -30.1 dB.6.3.3 Since the physical and electrical characteristics of a 384 kbit/s interface are identical to those of the 2048 kbit/sinterface, the jitter transfer function between the 2048 kbit/s input (El) and E3(synchronous 384 kbit/s) output isaccording to 6.3.1 above.8 Fascicle III.4 - Rec
47、. G.737Note 1 - The frequency f0should be less than 20 Hz and as low as possible (e.g. 10 Hz),taking into account the limitations of measuring equipmentNote 2 - To achieve accurate measurements the use of a selective method is recommendedwith a bandwidth sufficiently small referred to the relevant m
48、easurement frequency, but notwider than 40 Hz.Note 3 - For interfaces within national boundaries, this characteristic may be usedFIGURE 2/G.737Note 1 - The frequency f0should be less than 20 Hz and as low as possible (e.g. 10 Hz),taking into account the limitations of measuring equipment.Note 2 - To achieve accurate measurements, the use of a selective method is recommendedwith a bandwidth sufficiently small referred to the relevant measurement frequency, but notwider than 40 Hz.FIGURE 3/G.737Fascicle III.4 - Rec. G.737
