ITU-T G 794-1988 Characteristics of 24-Channel Transmultiplexing Equipments - General Aspects of Digital Transmission Systems Terminal Equipments (Study Groups XV and XVIII) 5 pp《2.pdf

1、CCITT FASCICLE 111.4 89 4862.593 0503783 3 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 the Recommendation cited in lo. This applies only to transmultiplexers with automatic internal l

2、evel regulation. Note 9 - The “system” fault condition corresponds to a fault on the transmultiplexer detected by the transmultiplexers supervision system, when it has one. Note 10 - The “synchronization” fault is that mentionned in 0 6 of the Recommendation G.793. When the transmultiplexer is synch

3、ronized with an external signal or with one of the two incoming PCM streams at 2048 kbit/s, the transmultiplexer should transmit an alarm signal in the event of synchronization loss. 121 131 i41 i51 171 i61 References CCIT Recommendation Recommendations concerning translating equipments, Vol. III, R

4、ec. G.233. CCIT Recommendation Pilots on groups, supergroups, etc., Vol. III, Rec. G.241. CCIT Recommendation Interruption control, Vol. VI, Rec. 4.416. CCITT Recommendation Recommendations relating to the accuracy of carrier frequencies, Vol. III, Rec. G.225. CCITT Recommendation Signal receiver, V

5、ol. VI, Rec. 4.415. CCIT Recommendation Signal sender, Vol. VI, Rec. 4.414. CCIT Recommendation Digital line signalling code, Vol. VI, Rec. 4.421, 8 3.1.2. CCIT Recommendation Conversion between analogue and digital versions of system R2 line signalling, Vol. VI, Rec. 4.430. CCIT Recommendation Inte

6、rruption control, Vol. VI, Rec. 4.416, $8 2.4.3.2 and 2.4.3.3. CCITT Recommendation Pilots on groups, supergroups, etc., Vol. III, Rec. G.241, 8 1. CCIT Recommendation Protection against the effect of faulty transmission on groups of circuits, Vol. VI, Rec. 4-33. Recommendation 6.794 CHARACTERISTICS

7、 OF 24-CHANNEL TRANSMULTIPLEXING EQUIPMENTS (Malaga- Torremolinos. 1984, amended at Melbourne. 1988) 1 Introduction The 24-channel transmultiplexer is a transmultiplexing equipment which satisfies Recommendations G.791 and G.792 and provides interconnection between a digital signal at 1544 kbit/s an

8、d two analogue basic groups (24-channel TMUX-P). 2 Digital interfaces 2.1 Coding law The coding law used is p-Iaw specified in Recommendation G.711. 2.2 Interfaces The 1544 kbit/s interfaces satisfy Recommendation G.703, 0 2. Fascicle 111.4 - Rec. G.794 595 CCITT FASCICLE 111.4 89 48b259L 0503784 3

9、H 2.3 Frame structure The 1544 kbit/s frame structure satisfies Recommendation G.704, 0 3.1.1. 2.4 Multifame structure The multiframe structure carried on the F-bit satisfies Recommendation G.704, 8 3.1.1. 3 Analogue interfaces 3.1 Ports The analogue interface consists of two 12-channel groups (band

10、 60-108 kHz) which satisfies Recommenda- tion G.232. The preferred signal levels at the group distribution frame satisfy Recommendation G.233. 3.2 Pilots The 24-channel transmultiplexer should transmit and receive the group pilot in Recommendation G.241. 3.3 Pilot detection and regulation The transm

11、ultiplexer may or may not regulate levels on the basis of the levels of the group pilots. If so, the transmultiplexer must meet the conditions of Recommendation G.241. 4 Correspondence between analogue and digital channels A fixed correspondence is established between the analogue and digital channe

12、ls. The following correspon- dence: PCM 1: Channels PCM 1: Channels Basic group 1 Basic group 2 to 12: 60-108 kHz 3 to 24: 60-108 kHz 5 Synchronization of transmultiplexer The transmultiplexer must produce virtual analogue carrier frequencies with the accuracy specified in For this purpose, it is re

13、commended: a) b) Recommendation G.225 (f either that the transmultiplexer should have an internal clock of sufficient accuracy; or that the transmultiplexer should be synchronizable with an external signal which may be: 1) 2) a frequency produced by a central generator: 4, 12, 124 kHz; or one of the

14、 incoming PCM streams which has sufficient accuracy (this may be the case, for example when this PCM stream 1544 kbit/s is produced by a TDM switching equipment). Note I - In the case of a digital filtering transmultiplexer, when synchronization on the incoming PCM stream is not possible, the remote

15、 digital terminal should have the sending side 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 externa

16、l sync signal, this internal oscillator is allowed 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 lop6. This is intended to allow the distant end digital terminal to receive an a

17、dequate frequency for alarm purposes only, so as not 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. 596 Fascicle nI.4 - Rec. 6.794 CCITT FASCIC

18、LE 111-4 89 = 4862571 0503785 5 = Note 3 - In the case where the transmultiplexer is to be used in a TDMA satellite application, the effect either, the TDMA terminal incorporates the Doppler buffer memories of appropriate capacity in the earth station to satellite direction. In this case, the two di

19、rections of the TMUX must be synchronized from one of the two 1544 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 of the two 1544 kbit/s streams t

20、ransmitted by the TDMA receive terminal. In the FDM to PCM direction, the 1544 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 by the TDMA transmit terminal

21、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. of the satellite Doppler frequency variation must be taken into account. Thi

22、s can be done in two ways: - - 6 Sign a 11 in g Two different approaches can be envisaged: 6.1 No signalling translation in TMUX This is applicable to applications such as in-band end-to-end signalling, and common channel signalling such as CCITT No. 6 or CCITT No. 7. 6.2 Translation of analogue sig

23、nalling (Recommendation Q.21) into I544 kbit/s PCM line signalling (Recommen- dation G. 733) This translation is applicable to the predomicant forms of analogue and digital signalling recommended by CCITT for international circuits (excluding signalling system R2) consisting of 12-channel analogue g

24、roups and 1544 kbit/s PCM digital signals. 7 Fault conditions and consequent actions The principle governing the handling of alarms is as follows: The behaviour of the 24-channel transmultiplexer vis-vis a 24-channel PCM multiplex equipment should be the same as that of another 24-channel PCM multip

25、lex equipment. Vis-vis a channel translator, it should behave like another channel translator. Table WG.794 summarizes the fault conditions and consequent actions in accordance with the frame structure, defined in Recommendation G.704. Fascicle II.4 - Rec. 6.794 597 - A CCITT FASCICLE 111.4 89 W 486

26、2591 0503786 TABLE 1/G.794 Fault conditions and consequent action for the 24-channel transmultiplexer Loss of frame alignment and multiframe alignment or Loss of incoming signai (2) Prompt Alarm maintenance indication to indication (7) equipment (3) alarm the remote I Yes (8) Yes Digital error ratio

27、 10- or (io) I Yes (8) I Yes Reception of alarm indication from the remote equipment (2, 3) Yes I AIS receiving (4) I yes I Absence of group pilot (5) Pilot level deviation alarm (i 1) Failure of power supply (2) I Yes I Yes, if regulation is present Yes I System failure (6) Yes Yes, depending on ne

28、twork applications I yes I Synchronization failure Blocking of sending faulty speech (4) channels Yes (PCM- FDM) Yes (PCM -+ FDM) Yes (9) Yes Yes, depending Yes, depending on on network network applications applications Pilot cut-off to the remote FDM terminal Yes, depending on network applications

29、Yes, depending on network applications Note 1 - A Yes in the table signifies that an action should be taken as a consequence of the relevant fault conditions. An open space in the table signifies that the relevant action should not be taken as a consequence of the relevant fault condition, if this c

30、ondition 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 of the conditions, a Yes is defined in relation to this action. Note 2 - The fault conditions Loss of incoming signal”, “Loss of frame alignment and

31、multiframe alignment”, “Reception of alarm indication to the remote equipment” and “Failure of power ,wpply” are defined in Recommendation G.733. Note 3 - For “Alarm indication to the remote equipment”, data link bits are used. Note 4 - The AIS can be used only in the new frame structure to be speci

32、fied by Study Group XVIII, Note 5 - The level, at which “Absence of group pilot” is detected, is under study. Note 6 - The “System failure”, which is only for the digital filtering transmultiplexer, corresponds to a fault detected by the transmultiplexers supervision system, when it has one. Note 7

33、- The consequent action “Prompt maintenance Alarm indication” and “Alarm indication to the remote equipment” are defined in Recommendation G.733. 598 Fascicle 111.4 - Rec. G.794 Nore 8 - When AIS is detected, the ?Prompt maintenance alarm indication? associated with the ?Loss of frame alignment and

34、multiframe alignment? with the ?Loss of incoming signal? or with the ?Digital error ratio Note 9 - The AIS is sent only if the 24 channels of a single PCM stream are in the alarm condition. Note 10 - Depends on network applications. Note I I - ?Pilot level deviation alarm? corresponds to a variation

35、 on the level of the incoming pilot from its nominal value by more than f 4 dB, as stated in CCI?TT Recommendation G.241, Q 1. This applies only to fransmultiplexers with automatic internal level regulation. should be blocked. Recommendation 6.795 a CHARACTERISTICS OF CODECS FOR FDM ASSEMBLIES (Mala

36、ga-Torremolinos, 1984, amended at Melbourne, 1988) - The CCI?IT, considering that codecs capable of encoding/decoding FDM assemblies will: a) b) c) be a useful element in the transmission networks of some Administrations during the period of transition from analogue to digital working; have a limite

37、d life and application; already be available in a number of realizations, recommends that FDM codea should conform with the following requirements: 1 General This Recommendation gives details of the analogue interfaces, the overall analogue-to-analogue perform- ance of a coder/decoder pair and certa

38、in details of the digital interfaces to which FDM codea should conform. The CCIT does not recommend any particular relationship between FDM assemblies and the digital hierarchies to be used in any codec realization nor does it recommend any particular frame structure or encoding law. Administrations

39、 intending to use codecs in their networks should ensure that compatible designs of codec are used at each end of a link. For international links, the codecs to be used should be by the agreement of the Administrations concerned. An Annex to this Recommendation gives details supplied by some Administrations of a number of FDM codec realizations. The application of FDM codea in a network is explained in Supplement No. 28. Fascicle III.4 - Rec. G.795 599 - c-