1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G0!30%#43G0G0/- unidirectional synchronous 320 kbit/s access (Figure 1b/G.739).The 320 kbit/s channel is based on the allocation of 5 x 64 kbit/s time slots, e.g. for setting up sound-programme circuits
2、 according to Recommendations J.43 and J.44. Because these circuits are specified as unidirectional,the equipment for insertion/extraction has to be separated as shown in Figure 1b/G.739.1 General characteristics1.1 Bit rateThe nominal bit rate is 2048 kbit/s. The tolerance on this rate is 50 parts
3、per million (ppm).1.2 Types of external accessa) Bidirectional synchronous insertion/extraction of 64 kbit/s data channels (see Figure l a/G.739).Note 1 - The timing signal for the insertion side should be derived from the 2048 kbit/s incoming signal atthe insertion side (I0); the timing signal for
4、the extraction side should be derived from the 2048 kbit/sincoming signal at the extraction side (El).Note 2 - The provision of a timing signal output, available for the purpose of synchronizing otherequipments, is an option that might be required depending upon national synchronization arrangements
5、.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 a320 kbit/s channel (see Figure l b/G.739).Note - The synchronous insertion equipment for 320 kbit/s signals requires
6、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 frequency of the analogue/digital converter.2 Frame structure and use of derived channel time slots2.1 F
7、rame 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 Use of derived channel time slotsTime slots not accessed flow transparently through the equipment.No
8、te - 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 Fascicle III.4 - Rec. G.7392.2.1 64 kbit/s accessThe number of accessible channel time slots should be at least four and
9、 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 of priority: 6 -22 - 14 - 30 - 2 - 18 - 10 - 26 - 4 - 20 - 12 - 28 - 8 - 24 - 5 - 21 - 13 - 29 - 1 - 17 - 9 - 25
10、 - 3 - 19 - 11 - 27 - 7 - 23 - 15 -31.a) Bidirectional synchronous insertion/extraction of 64 kbit/s data channelsb) Unidirectional synchronous insertion and extraction of digital sound-programme (DSP) signal into/out of a 320 kbit/s channelI0, I1Insertion side I3, E3Synchronous digital sound-progra
11、mme signal accessE0, E1Extraction side T Timing signalI2, E264 kbit/s interfaceFIGURE 1/G.739External access equipment for 64 and 320 kbit/s channelsFascicle III.4 - Rec. G.739 32.2.2 320 kbit/s accessThe time slot allocation for digital channels with bit rate at 320 kbit/s is given in Table 1/G.739
12、.TABLE 1/G.739320 kbit/s channels (Note 1) Digitalsound-programmeABCDEFaccess points1 - 2 -3 - 4 -56 - 7 -8 - 9 -1011 - 12- 13 -14 - 1517 - 18- 19 -20 - 2122 - 23- 24 -25 - 2627 - 28- 29 -30 - 31I3, T, E3Figure 1b/G.738Note 1 - The six possible 320 kbit/s channels in a 2048 kbit/s stream are numbere
13、d A to F. Preferably the channel pairs A-B, C-D and E-F should be used for stereophonic 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 usedfor purposes other than a voice channel encoded within the PCM multipl
14、ex equipment.3 Frame alignment and CRC procedures both at insertion (I0) and extraction (El) 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 CR
15、C multiframe alignment in TSORefer to 4.2 of Recommendation G.706.3.4 CRC bit monitoringRefer to 4.3 of Recommendation G.706.4 Fault conditions and consequent actions4.1 Fault conditionsThe equipment should detect the following conditions:4.1.1 Failure of power supply.4.1.2 Loss of incoming signal a
16、t I2or I3.Note - This detection is not mandatory when contradirectional interfaces are used.4 Fascicle III.4 - Rec. G.7394.1.3 Loss of the incoming signal at 2048 kbit/s both at insertion (I0) and extraction (El) sides.Note 1 - The detection of this fault condition is required only when it does not
17、result in an indication of loss offrame alignment.Note 2 - Where separate circuits are used for the digital 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 (El) sides.4.1.5 Exces
18、sive bit error ratio detected by monitoring the frame alignment signal at both 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
19、a random bit error ratio of 10-4, the probability of activating the indication 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
20、 With a random bit error ratio of 10-3, the probability of deactivating the indication 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.Not
21、e - The activating and deactivating period specified as “a few seconds“ is intended to be in the order of4 to 5 seconds.4.2 Consequent actionsFurther to the detection of fault condition, appropriate actions should be taken as specified in Table 2/G.739.The consequent actions are as follows:4.2.1 Pro
22、mpt maintenance alarm indication generated to signify that performance is below acceptable standards andmaintenance attention is required locally. When the AIS at the 2048 kbit/s inputs (I0, El) is detected (see General Notesbelow to 4.2), the prompt maintenance alarm indication associated with loss
23、 of frame alignment (see 4.1.4) andexcessive error rate (see 4.1.5) should be inhibited, while the rest of the consequent actions are in accordance withthose associated in Table 2/G.739 with the two fault conditions.Note - The location and provision of any visual and/or audible alarm activated by th
24、e alarm indications given in 4.2.1 is left to the discretion of each Administration.4.2.2 AIS applied to E2, 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 tim
25、e slots in the composite 2048 kbit/s output signal at insertion side (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 o
26、f application of this equipment in anetwork and therefore is not mandatory.Fascicle III.4 - Rec. G.739 54.2.6 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 n
27、ot mandatory.4.2.7 AIS applied to the 2048 kbit/s output, insertion side (I1).Note - The provision of this consequent action depends on the type of this equipment in a network and thereforeis not mandatory.General Notes to 4.2Note 1 - The equivalent binary content of the alarm indication signal (AIS
28、) is a continuous stream of binary 1s.The strategy for detecting the presence 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 x 10-3. Nevertheless, a signal in which all the binaryelements, with the excepti
29、on of the frame alignment signal, are in the state 1, should not be taken 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
30、 digital interfaces at 64 kbit/s should be either of the codirectional or the contradirectional type specified inRecommendation G.703.The need to define a digital interface operating at 320 kbit/s is under study.Note 1 - It should be noted that according to the principle of minimizing the number of
31、different types ofinterfaces, the information rate of 320 kbit/s will be 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
32、should take into account theneed to provide octet alignment, to allow controlled 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.739TABLE 2/G.739Fault
33、 conditions and consequent actions for the external access equipmentConsequent actions (see 4.2)Fault conditions (see 4.1) Promptmaintenancealarms indicationgeneratedAIS applied to E2or E3outputsInhibition ofdigitalinformationinsertionI2, I3AIS applied to therelevant time slot of the2048 kbit/s comp
34、ositesignal at insertion side(I0)Both 2048 kbit/ssignals are bypassed(see Note 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)Y
35、es(if practicable)Loss of incoming signal at I2or I3 inputs (see Note under 4.1.2)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 ofRec. G.706, 4.2)Ins.s. (I0) Yes(see 4.2.1)Yes YesError rati
36、o1 10-3on theframeExtr.s. (E1) Yes(see 4.2.1)Yes Yesalignmentsignal (seeNote under 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 action
37、 should not be taken as aconsequence 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 should be taken if, for at least one ofthe conditions, a Yes is defined in relation to this action.Fascicle
38、 III.4 - Rec. G.739 76 Jitter6.1 Jitter at 2048 kbit/s outputWhen there is no jitter on the 2048 kbit/s inputs (I0, El) 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 fl= 20 Hz to f4= 100 kHz. Theequivalent bin
39、ary content of the test signal applied at the 2048 kbit/s input shall be a pseudo-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.
40、6.2 Jitter at E2and E3outputs6.2.1 The jitter at the E2(64 kbit/s) output when there 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= 100 kHz. The equivalent binary content ofthe test signal applied at the 2048 kbit/s
41、 input shall be a pseudo-random bit sequence of length 215 - 1 as specified inRecommendation 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
42、and electrical characteristics of a 320 kbit/s interface are identical to those of the 2048 kbit/sinterface, the jitter at the E3(synchronous 320 kbit/s) output when there is no jitter at the 2048 kbit/s input (El) isaccording to 6.1 above.6.3 Jitter transfer functions6.3.1 The jitter transfer funct
43、ion between the 2048 kbit/s input (I0, El) and the output (Il, E0) should not exceed thegain/frequency limits given in Figure 2/G.739.Some Administrations require that equipment be fitted with jitter reducers. In this case, the jitter transferfunction should not exceed the gain/frequency limits give
44、n in Figure 3/G.739.Note 1 - The 2048 kHz signal shall be modulated with sinusoidal 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 tr
45、ansfer function between the 2048 kbit/s input (El) and the E2(64 kbit/s) output should 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
46、1 - The 2048 kbit/s test signal shall be modulated by sinusoidal jitter. The equivalent 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
47、 test signal.Note 3 - The jitter reduction of 1/32 due to demultiplexing is equivalent to -30.1 dB.6.3.3 Since the physical and electrical characteristics of a 320 kbit/s interface are identical to those of the 2048 kbit/sinterface, the jitter transfer function between the 2048 kbit/s input (El) and
48、 E3(synchronous 320 kbit/s) output isaccording to 6.3.1 above.8 Fascicle III.4 - Rec. G.739Note 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 selecti
49、ve method is recommendedwith a bandwidth sufficiently small referred to the relevant measurement frequency, but notwider than 40 Hz.Note 3 - For interfaces within national boundaries, this characteristic may be used.FIGURE 2/G.739Note 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 f
