1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G0,%!3%$G0G0#)2#5)43,).).G0G050G0G0!.G0G0).4%2.!4)/.!,-5,4)4%2-).!,G0G0,%!3%$G0G0#)2#5)4)45G134G0G0RecommendationG0G0- (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation M.105
2、5 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 and copyright conditions remain unchanged
3、 (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 or utilized in any form or by any mean
4、s, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.2 - Rec. M.1055 1Recommendation M.1055Fascicle IV.2 - Rec. M.1055LINING UP AN INTERNATIONAL MULTITERMINALLEASED CIRCUITThese circuits are usually arranged in one of the following
5、ways:UnidirectionalOne station may transmit to every other and receive from every other, but the other stations have nocommunication among themselves. That is, the circuit is in effect a combination of a distribution network and acontribution network. This arrangement is used to interconnect, for ex
6、ample, a computer centre with outlying userstations.ConferenceAny station may have two-way transmission with any other. This usually implies that any station may inprinciple have two-way transmission with every other station simultaneously, and for telephony, some sort of selectivesignalling is empl
7、oyed. An example of this arrangement is the multiterminal speaker facilities provided for stations onimportant submarine cable schemes.A systematic procedure is needed to line up this class of circuit if needless readjustment of interdependentapparatus is to be avoided.1 Multiterminal unidirectional
8、 circuits1.1 Distribution networkThe explanation of the principle is given in terms of Figure 1/M.1055 which illustrates part of the distributionnetwork (i.e. the sending direction of transmission) emanating from station A. (There may be similar networks alsoemanating from station A, but these can b
9、e treated as this one, thus there is no loss of generality in assuming that stationA is at one end of the network.)d01-scFIGURE 1/M.1055.D012 Fascicle IV.2 - Rec. M.1055The sections a to z are point-to-point circuits or circuit sections, each of which may be composed of national orinternational sect
10、ions.The order in which the distribution network is lined up and connected together is as follows:a) Identify the path with the greatest number of sections: in the example, this is a-b-c-d-e-f-g-h.(Note A-M may be longer geographically, but has only 5 sections, whereas A-R has 8 sections.)b) Identif
11、y the next longest path remaining (i.e. imagine the path A-R to be removed with its branchingpoints. This is taken to be j-k-l (the distance 2-E is assumed to be greater than the distance 2-F thoughboth of them have three sections).c) Identify the remaining paths in order of length. In the example,
12、these are all the single sections i, m, n, . . .y, z.d) When the network is separated in this fashion, the pathsa-b-c-d-e-f-g-h,j-k-l,i,m,n,.y,zmay all be lined up concurrently according to the principle of Recommendation M.1050.e) With a measurement-tone at a suitable level connected to A, add on t
13、he following branches (concurrently,if possible): at 1 the branches m and n; at 2 the branches j-k-l, r and s; at 3 the branches t and u; at 4 the branches v and i;making any necessary adjustments.f) Stations 8 and 9 now add on branches p, q, and o, adjustments being made if necessary.1.2 Contributi
14、on networkThis is much more difficult to organize because the outstations may only send one at a time. The problem iseased if the network is divided into more manageable portions. A possible scheme related to Figure 1/M.1055 (with allthe arrows assumed to be reversed) would be as follows:a) The long
15、est paths h-g-f-e-d-c-b-a and o-k-j are lined up concurrently as before.b) Keeping e disconnected at 4, stations N, O, P and Q send to 4 in turn, stations 5, 6 and 7 making anynecessary adjustments to branches w, x, y and z.Fascicle IV.2 - Rec. M.1055 3c) Concurrently with b) above, stations D, G an
16、d E send to 2 in turn (j disconnected) with 8 and 9 makingany necessary adjustments to sections p, q and l.d) Concurrently with b) and c) above, stations M, L, J and K send to station 3 (c disconnected) withstations 3 and 4 making any necessary adjustments to sections i, v, t and u.e) Concurrently w
17、ith b), c) and d), stations B, C, H and I send in turn to station A with stations 1 and 2making any necessary adjustment to sections m, n, r and s.1.3 It is recommended that the Administration of the country in which the focal station is situated should beresponsible for drawing up the schedule show
18、ing the order in which the various circuit sections should be lined up.1.4 If the circuit requires to be equalized then a very precise order in which the sections are to be equalized andconnected together will be necessary if needless readjustment is to be avoided.1.5 In order to apply the principle
19、s of equalizing outlined in Recommendation M.1050 it will be necessary toidentify paths in the circuit connecting the focal station to each of the outstations and to treat each path as apoint-to-point circuit bearing in mind 1.4 above.2 Multiterminal conference circuits2.1 These are usually provided
20、 by means of bidirectional branching units which are inserted into the two directionsof transmission of a 4-wire circuit and derive a send and receive pair.2.2 It is recommended that the branching units are designed to enable a branch to be added without affecting thelevels of the main circuit.2.3 T
21、he line-up should be organized so as to avoid needless readjustment of circuit sections. This principleoutlined for multiterminal unidirectional circuits gives guidance in this matter.2.4 Four-wire telephones should be used whenever possible to avoid instability problems.There should be some limit to the number of locations joined together (for example: 12).
