1、CCITT FASCICLE 111.4 89 4Ab2591 0503775 2 Note I - Burst tones do not occur in the call channel after call set-up has taken place. Note 2 - Burst rates are in the order of 10 to 25 Hz. Note 3 - Charge metering pulses are of long duration, e.g. 150/450 ms and are evaluated as a continuous References
2、CCITT Recommendation Recommendations relating to the accuracy of carrier frequencies, Vol. III, Rec. G.225, 8 1. CCITT Recommendation Pilots on groups, supergroups, etc., Vol. III, Rec. G.241, 4 1. Ibid., !j 2. Zbid., 8 3. CCIT Recommendation Assumptions for the calculation of noise on hypothetical
3、reference circuits for telephony, Vol. III, Rec. G.223, Table 3/G.223, 8 6. CCIT Recommendation Measurement of circuit noise in cable systems using a uniform-spectrum random noise loading, Vol. III, Rec. G.228, $9 A.l, A.2.2. CCIT Recommendation Assumptions for the calculation of noise on hypothetic
4、al reference circuits for telephony, Vol. III, Rec. G.223, 8 2.1. CCITT Recommendation Measuring method and through-connection filters for noise produced by modulating equipment, Vol. III, Rec. G.230. CCIR Recommendation Measurement of performance by means of a signal of a uniform spectrum for syste
5、ms using frequency-division multiplex telephony in the fixed satellite service, Vol. IV, Rec. 482, ITU, Geneva, 1978. CCITT Recommendation Assumptions for the calculation of noise on hypothetical reference circuits for telephony, Vol. III, Rec. G.223, 8 7. CCIT Recommendation Conventional telephone
6、signal, Vol. III, Rec. G.227. CCITT Recommendation Il-channel terminal equipments, Vol. III, Rec. G.232, $8 5.1, 5.2. CCIT Recommendation Through-connection of groups, supergroups, etc., Vol. III, Rec. G.242, 8 1. CCITT Recommendation 12-channel terminal equipments, Vol. III, Rec. G.232, $8 12.1, 12
7、.2 and Annex A. CCIT Recommendation Signal sender, Vol. VI, Rec. 4.414, Figure 6/Q.414. CCIT Recommendation 12-channel terminal equipments, Vol. III, Rec. G.232. Ibid., !j 12.3 and Annex B. CCIT Recommendation 1020 Hz reference test frequency, Vol. IV, Rec. 0.6. Recommendation G.793 CHARACTERISTICS
8、OF 60-CHANNEL TRANSMULTIPLEXING EQUIPMENTS (Geneva, 1980; further amended) 1 Introduction The 60-channel transmultiplexer is a transmultiplexing equipment which satisfies Recommendations G.791 and G.792 and provides interconnection between two digital signals at 2048 kbit/s and an analogue supergrou
9、p (60-channel TMUX-S). 2 Digital interfaces 2.1 Coding law The coding law used is A-law specified in Recommendation G.711. 2.2 Interfaces The 2048-kbitIs interfaces satisfy Recommendation G.703, 0 6. Fascicle 111.4 - Rec. G.793 587 - CCITT FASCICLE 111.4 89 m 4862591 O503776 4 m 2.3 Frame structure
10、The structure is specified in Recommendation G.704, Q 3.3.1. The strategy and the criteria for loss and recovery of frame alignment satisfy Recommendation G.706, 0 4.1. 2.4 Multifame structure The multiframe structure of time slot 16 satisfies Recommendation G.704, 8 3.3.3. The strategy and the crit
11、eria for loss and recovery of multiframe alignment satisfy Recommendation G.732, Q 5.2. 3 Analogue interfaces 3.1 Ports The analogue interface consists of a 60-channel supergroup (band 3 12-552 kHz) which satisfies Recommen- The preferred signal levels at the supergroup distribution frame should be:
12、 - for sending -36 dBr - for receiving -30 dBr The impedances are: 75 ohms (unbalanced). dation G.233 i. 3.2 Pilots The 60-channel transmultiplexer should transmit the following pilots: TMUX-S: A supergroup pilot with a frequency 411 920 Hz and a level of -20 dBmO, one pilot per group with a level o
13、f -20 dBmO and frequencies of: Group 1: 335 920 Hz Group 2: 383 920 Hz Group 3: 431 920 Hz Group 4: 479 920 Hz Group 5: 527 920 Hz The transfer of pilot alarms individually for each group in a supergroup and the consequence for the split channels of group 3 can be seen in Figure 1 of Supplement No.
14、32. Other sets of pilots as recommended in Recommendation G.241 can be used. Special attention should be given to the compatibility of the set of pilots adopted with the out-of-band signalling system using a frequency at 3825 Hz. The characteristics relating to the generation and transmission of the
15、se pilots are given in Recommenda- tion G.241 2. 3.3 Pilot detection and regulation The transmultiplexer may or may not regulate levels on the basis of the levels of the group and supergroup pilots. If so, the transmultiplexer must meet the conditions of the Recommendation cited in 2. Detection of t
16、he levels of the group pilots and or supergroup mentioned in Q 3.2 should, however, be effected to ensure operation of the interruption control system (Recommendation 4.416 3), when R2 signalling is used. 4 Correspondence between- analogue and digital channels A fixed correspondence is established b
17、etween the analogue and digital channels. The correspondence shown in Table 1/G.793 (which facilitates the transfer of alarms and results in a natural order of the channels on the analogue side) is recommended. 588 Fascicle HI.4 - ,-A Rec. G.793 CCITT FASCICLE 111.4 A9 4Ab259L 0503777 b W TABLE i/G.
18、793 PCM i channels 1 to 12 Group i 3 12-360 kHz PCM 1 Group 2 channels 13 to 24 360-408 kHz PCM 1 Group 3 channels 25 to 30 408-432 kHz PCM 2 channels 1 to 6 Group 3 432-456 kHz PCM 2 channels 7 to 18 Group 4 456-504 kHz PCM 2 Group 5 channels i9 to 30 504-552 kHz Note - In national netwoiks or by a
19、greement between Adminis- trations, other schemes of correspondence between analogue and digital channels may be used. 5 Plesiochronous operation of incoming PCM streams Sixty-channel transmultiplexers should be able to accept two mutually plesiochronous incoming PCM In the case of transmultiplexers
20、 with digital filtering, this means that the two input ports at 2048 kbit/s are fitted with frame aligners (jump or repetition of samples) and multiframe aligners for synchronizing the incoming PCM streams with the transmultiplexer clock. In order to avoid a major slip frequency, the two incoming PC
21、M streams should be either synchronous with the transmultiplexer or plesiochronous with each other and with the transmultiplexer clock, so that Recommendation G.8 11 on the plesiochronous network is satisfied. streams within the limits laid down in Recommendation G.703 (bit rate 2048 kbit/s, f 50 6
22、Synchronization of transmultiplexer The transmultiplexer must produce virtual analogue carrier frequencies with the accuracy specified in For this purpose, it is recommended: a) b) Recommendation G.225 4 (f IOp7). either that the transmultiplexer should have an internal clock of sufficient accuracy;
23、 or that the transmultiplexer should be synchronizable with an external signal which may be: 1) a frequency (see Note 3) produced by a central FDM generator: 4, 12 or 124 kHz; 2) or one of the incoming PCM streams which has sufficient accuracy (this may be the case, for example, when this PCM stream
24、 at 2048 kbit/s is produced by a TDM switching equipment). If both 2048-kbit/s streams are of sufficient accuracy, the use of PCM stream No. 1 is preferred. In most cases this avoids, at the digital filtering transmultiplexer input, the slipping phenomena which, when too frequent, cause high error r
25、ates on in-band data signals. Fascicle III.4 - Rec. G.793 589 -_ CCITT FASCICLE 111.4 89 m 4862573 0503778 8 m Note I - In the case of a digital filtering transmultiplexer, when synchronization on one of the incoming PCM streams is not possible, the remote digital terminal should have the sending si
26、de synchronized with the receiving side so as to avoid slipping at the transmultiplexer input. Note 2 - In the case of external synchronization, transmultiplexers often have an internal oscillator locked to the external signal, If, upon loss of the external sync signal, this internal oscillator is a
27、llowed to continue to supply the clock for the outgoing digital signal (now in the free-running mode), then this oscillator should have a minimum free-running accuracy of 50 x This is intended to allow the distant end digital terminal to receive an adequate frequency for alarm purposes only, so as n
28、ot to confuse maintenance and trouble-shooting activities. Also, a local alarm should be given in the event of a fault in the synchronization system or in the absence of the external synchronization signal (Tables 2/G.793, 3/G.793 and 2 of Supple- ment No. 32). Note 3 - In the case where the transmu
29、ltiplexer is to be used in a TDMA satellite application, the effect of the satellite Doppler frequency variation must be taken into account. This can be done in two ways: either, the TDMA terminal incorporates the Doppler buffer memories of appropriate capacity in the earth station to satellite dire
30、ction. In this case, the two directions of the TMUX must be synchronized from one of the two 2048 kbit/s PCM streams transmitted by the TDMA receive terminal: or, the TDMA terminal does not incorporate Doppler buffers. In this case, the PCM to FDM direction of the TMUX may be synchronized from one o
31、f the two 2048 kbitls streams transmitted by the TDMA receive terminal. In the FDM to PCM direction, the 2048 kbit/s streams transmitted by the TMUX must be made synchronous with the TDMA system transmit clock: this supposes that a synchronization signal (contradirectional with the data) is provided
32、 by the TDMA transmit terminal to the TMUX. In the case where the processing in a digital filtering transmultiplexer is made synchronously for the two directions, Doppler buffer memories of appropriate capacity must be incorporated in the PCM interfaces. 7 7.1 7.2 Signalling Different kinds of signa
33、lling systems can be envisaged. In-band signalling The 60-channel transmultiplexer is transparent for channel-associated in-band signalling. Common channel signalling In the case when common channel signalling must be routed through the transmultiplexer, attention is drawn to the fact that the trans
34、mission capabilities of a channel in the transmultiplexer is limited to the band 300-3400 Hz (Le. data rates corresponding to this frequency band). Information on signalling bit rates is given in 0 2 of Recommendation 4.702. In the opposite case, when common channel signalling is not routed through
35、the TMUX, no special problems are recognized. 7.3 Out-of-band signalling As regards Signalling System R2, signalling conversion between the analogue and digital versions of line signalling as recommended in Recommendation 4.430 is to be used in the case of international interconnection and should co
36、nform to the following specifications. The transmultiplexer, or an additional equipment associated with it, converts the analogue version to the 2-bit digital version of the R2 line Signalling System, and vice versa. In all cases, the transmultiplexer should provide the following facilities for sign
37、alling: a) Analogue side 1) recognition of the signalling frequency at 3825 Hz in accordance with Recommenda- tion 4.415 5: 2) transmission of the signalling frequency at 3825 Hz in accordance with Recommenda- tion 4.414 6; 3) supervision of group pilots (and supergroup pilots if necessary) in accor
38、dance with Recommen- dation 4.416 3. 590 Fascicle IIi.4 - Rec. G.793 CCITT FASCICLE 111.4 89 W 48b2571 0503779 T W b) Digital side 1) extraction of signalling bits a and b of time slots 16 received in accordance with the Recommendation cited in 7; 2) insertion of appropriate signalling data in bits
39、a and 6 of time slots 16 transmitted in accordance with the Recommendation cited in 7; 3) detection of PCM system faults. The conversion between the analogue and digital versions of the R2 line Signalling System should be made in accordance with 8. When the conversion is made in an external equipmen
40、t, the transmultiplexer should supply the necessary ports. For national networks, a method of using the analogue line signalling version on both analogue and digital transmission systems is described in Supplement No. 32. 8 Fault conditions and consequent action 8.1 Principles of the action to be ta
41、ken The principles governing the handling of alarms is as follows : The behaviour of a transmultiplexer vis-vis a 30-channel PCM multiplex should be the same as that of another 30-channel PCM multiplex. However, the transmultiplexer performs certain functions peculiar to digital multiplexing equipme
42、nts such as the trans- mission of the Alarm Indication Signal (AIS). Vis-vis a group modulator, it should behave like another group modulator. The principles of alarm transfer are described in Supplement No. 32 which also contains particular solution used in national networks. 8.2 Digital version of
43、 R2 signalling system Table 2/G.793 summarizes the fault conditions and the consequent actions. 8.3 In-band signalling and common channel signalling Table 3/G.793 summarizes the fault conditions and the consequent actions (see Note). Note - The problem of per channel alarm transfer needs further stu
44、dy. For applications where the TMUX is used in TDMA configuration, Recommendation 4.33 should be considered i i. Fascicle 111.4 - Rec. G.793 59 1 CCITT FASCICLE 111-4 89 m 48b2591i 0503780 b m h W o Y z z o 8 W Y a ? a z Y Y O - h d o Y z o 2 W h d B P z o W Y O R (ci O o - -3 E a 8 3 II II D d .+ I
45、I P II d E E Sf E 2 I O h m B 8 z o W Fascicle 111.4 - Rec. 6.793 CCITT FASCICLE 111.4 87 m 4862573 0503783 B m Note 2 - The fault conditions “Loss of signal at 2 Mbit/s”, “Error ratio “Loss of frame alignment”, “Loss of multiframe alignment”, “Reception of bit 3, time slot O”, “Reception of bit 6,
46、fime slot 16, frame O” and the consequent action “Bit 3, time slot O to l”, “Bit 6, time slot 16, frame O to l”, “Bit 6, time slot 16, frame O to 1” and “AIS sent” are defined in Recommendation (3.732. Note 3 - The 60-channel transmultiplexer should be able to detect the alarm indication signal (AIS
47、) on incoming streams at 2048 kbit/s. When AIS is detected, the prompt maintenance indication associated with the loss of frame alignment, with an excessive error rate or with the loss of multiframe alignment should be blocked. Note 4 - This action is not necessary when the digital version of Signal
48、ling System R2 is used, but may be useful with other applications. Note 5 - The definition of absence of group pilot used for the operation of the interruption control system is given in the Recommendation cited in 9. The supergroup pilot can also be used. Note 6 - The AIS is sent only if the 30 cha
49、nnels of a single PCM stream are in the alarm condition. Note 7 - Detection of “absence of supergroup pilot” is not obligatory. If the supergroup pilot is not sent, this alarm function can be performed by supervision of the 5 group pilots. Note 8 - The concept of pilot level deviation alarm corresponds to a variation on the level of the pilot from its nominal value by more than f 4 dB, as stated in lo. This applies only to transmultiplexers with automatic internal level regulation. Note 9 - The “system” fault condition corresponds to a fault on the tra
