1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G04%,%2!0(G0G03934%-3!.$G0G00(/4/4%,%2!0(G0G042!.3-)33)/.).4%2.!4)/.!,G0G04)-%G0G0$)6)3)/.-5,4)0,%8G0G0 4$-G9G0G04%,%2!0(3934%-3)45G134G0G0RecommendationG0G0- (Extract from the “LUE
2、G0“OOK)NOTES1 ITU-T Recommendation M.850 was published in Fascicle IV.2 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version an
3、d copyright conditions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced
4、 or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.2 - Rec. M.850 1Recommendation M.850Fascicle IV.2 - Rec. M.850INTERNATIONAL TIME DIVISION MULTIPLEX (TDM)TELEGRAPH SYSTEMS1 General descript
5、ion of an international TDM system1.1 Figure 1/M.850 illustrates a basic international TDM telegraph system. The system operates via aninternational TDM telegraph link operated at 2400 bit/s and has a capacity of 46 telegraph channels at 50 bauds. Othermodulation rates up to 300 bauds can be accommo
6、dated (with resulting reduction in channel capacity) as shown inRecommendation R.101, Table 1/R.101 1.1.2 The international TDM telegraph system may be carried over a dedicated voice-frequency link as shown inFigure 1/M.850 or multiplexed with other TDM systems or other services onto a higher bit ra
7、te data transmission systemon a voice-frequency or digital data transmission link as shown in Figure 2/M.850.1.3 International telegraph systems may also be carried on high level (e.g. 50, 56 kbit/s) data transmission linksutilizing analogue group band or on digital (64 kbit/s) paths. Examples of su
8、ch multiplexing arrangements are illustratedin Recommendation M.1300.2 Basic TDM telegraph links (Figure 1/M.850)2.1 Basic TDM telegraph links may be carried on 4-wire analogue telephone circuits. The link comprises twounidirectional transmission paths, one for each direction of transmission, betwee
9、n the terminal TDM telegraphequipments. The TDM telegraph links are terminated with data modems, usually (but not necessarily) located within theterminal TDM telegraph equipment, which operate at 2.4 kbit/s.2.2 The international TDM telegraph link consists of an international TDM telegraph line toge
10、ther with anyterminal national sections connecting the international line to the terminal TDM telegraph equipment. Where theTDM equipment is located in the terminal international centres, the TDM link consists only of the internationalTDM telegraph line.2.3 The international TDM telegraph line (betw
11、een terminal international centres) may be constituted by using achannel in a carrier group or channels in tandem on a number of groups. National and international sections can beinterconnected to set up an international TDM telegraph link.Wherever possible, an international TDM telegraph line shoul
12、d be provided on a channel of a single carriergroup, thereby avoiding intermediate audio-frequency points. However it is recognized that in some cases such a directgroup may not exist or, for special routing reasons, it may not be possible to set up the international TDM line in thispreferred way.2.
13、4 Terminal national sections connected to the international TDM telegraph lineIn some cases the TDM telegraph terminal equipment is remote from the terminal international centre of theinternational TDM telegraph line (Figure 1/M.850), and such cases necessitate the provision of terminal national sec
14、tionsin order to establish international TDM telegraph links. These sections may be routed on channels of carrier groups or onaudio plant (amplified or unamplified) or on digital streams.3 TDM telegraph links multiplexed on higher bit rate data systems (Figure 2/M.850)3.1 When TDM telegraph links ar
15、e multiplexed onto higher bit rate data transmission systems, the associatedanalogue voice-frequency data links generally follow the principles outlined in 2, with the exception that these datalinks are operated at higher bit rates (usually 4.8, 7.2 or 9.6 kbit/s).Should a TDM telegraph link be exte
16、nded from the higher level multiplexer, for example, to a remote pointsuch as a third country or to renters premises, then it is necessary to use an appropriate modem as shown inFigure 2/M.850.2 Fascicle IV.2 - Rec. M.850d01-scFIGURE 1/M.850.D01d02-scFIGURE 2/M.850.D02Fascicle IV.2 - Rec. M.850 33.2
17、 TDM telegraph links multiplexed onto voice-frequency data transmission systems operated at 4.8, 7.2 or9.6 kbit/s may be further multiplexed onto higher bit rate data transmission systems operated at 50, 56, 64 kbit/s etc.Examples of such arrangements are shown in Recommendation M.1300.4 Characteris
18、tics, line-up, and maintenance of TDM telegraph links and systems4.1 Characteristics and line-upGuidance on the transmission characteristics and line-up procedures for both analogue and digital TDMtelegraph links may be found in Recommendation M.1350, 2 and 3. In this regard, the TDM telegraph link
19、is identicalto a 2.4 kbit/s data transmission link.4.2 MaintenanceMaintenance procedures and limits for both analogue and digital TDM telegraph links may be found inRecommendation M.1355.Maintenance procedures and limits for TDM telegraph systems are under study. However, guidance on themaintenance
20、of these systems may be found in Recommendations R.75 2 and V.51 to V.53 3.5 Reserve arrangements for TDM telegraph links5.1 General requirementsAll necessary action should be taken to ensure that the number of interruptions on TDM telegraph systems bekept to a minimum, and further that interruption
21、s, when they do occur, be kept as short as possible.5.2 Basic international telegraph linksReserve arrangements for international TDM telegraph systems operated over links at 2.4 kbit/s should be inaccordance with the principles and procedures specified for international voice frequency telegraph sy
22、stems. Refer toRecommendation M.800, 2. In some instances, it may be desirable to establish dual, diversely routedinternational TDM telegraph links and to change over from the active link to the reserve link when the internationalTDM telegraph system fails or becomes degraded. The change over may be
23、 done automatically, semi-automatically, ormanually, by agreement between Administrations involved. Guidance on changeover arrangements may be found inRecommendations M.800 and R.150 4.5.3 TDM telegraph links multiplexed on higher level data transmission systemsWhen international TDM telegraph links
24、 are multiplexed onto higher bit rate data transmission systems,reserve arrangements will normally depend upon the principles and procedures adopted for the higher level datatransmission link. Reserve arrangements for these data transmission links require further study.6 TDM telegraph link designati
25、onThe form of designation for the TDM telegraph link and its reserve is given in Recommendation M.140, 1.2.2 5.7 Marking of equipment associated with TDM telegraph linksIt is recommended that all equipment associated with the TDM telegraph link and nominated reserve circuits(channel translating equi
26、pment, distribution frames, etc.) be positively marked to make them readily identifiable to themaintenance staff.8 TDM telegraph link control and sub-control stations8.1 One control station should be agreed bilaterally between the Administrations involved for each TDM telegraphlink prior to setting
27、up the link. Principles concerning the definition, responsibilities, functions, and appointment ofcontrol stations may be found in Recommendation M.1012.8.2 One sub-control station should be agreed bilaterally between Administrations involved for each TDMtelegraph link prior to setting up the link.
28、Principles concerning the definition, responsibilities, functions, andappointment of sub-control stations may be found in Recommendation M.1013.4 Fascicle IV.2 - Rec. M.850References1 CCITT Recommendation Code and speed dependent TDM system for anisochronous telegraph and datatransmission using bit
29、interleaving, Vol. VII, Rec. R.101.2 CCITT Recommendation Maintenance measurements on code independent international sections ofinternational telegraph circuits, Vol. VII, Rec. R.75.3 CCITT Recommendations on the Maintenance of international telephone Type circuits used for datatransmissions, Vol. V
30、III, Recs. V.51 to V.53.4 CCITT Recommendation Automatic protection switching of dual diversity bearers, Vol. VII, Rec. R.150.5 CCITT Recommendation Designation of international circuits, groups, group and line links, digital blocks,digital paths, data transmission systems and related information, Vol. IV, Rec. M.140.
