1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G042!.3-)33)/.G0G03934%-3!.!,/5%G9.5-“%2).G0G0).G0G03934%-3/.G0G039-%42)#G0G00!)2G0G0#!“,%)45G134G0G0RecommendationG0G0- (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation M.3
2、90 was published in Fascicle IV.1 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 unchange
3、d (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 mea
4、ns, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.1 - Rec. M.390 1Recommendation M.390Fascicle IV.1 - Rec. M.390NUMBERING IN SYSTEMS ON SYMMETRIC PAIR CABLE1 Systems providing 12 telephone carrier circuits on a symmetric pair in
5、 cable (12 + 12) systemsIn systems of the 12 + 12 type, 12 go and 12 return channels constitute one 12 circuit group.For the arrangement of the line frequencies transmitted for 12 + 12 cable systems using transistors, theAdministrations concerned in setting up such an international system can make t
6、heir choice from scheme 1 or scheme 2of Figure 1/M.390. Systems using scheme 2 can use only pilot frequencies of 54 kHz or 60 kHz.d01-scFIGURE 1/M.390.D01Figure 1/M.390 also applies to (12 + 12) systems using valves, provided that in the case of scheme 2 theindicated line-regulating pilots of 54 kHz
7、 and 60 kHz, or 30 kHz and 84 kHz, can be chosen as pilot frequencies.2 Systems providing five groups or less2.1 Numbering in systems comprising both erect and inverted groups2.1.1 Designation of groupsThe following indications are used to define the position of the group on the line, as shown in Fi
8、gure 2/M.390:A: 12-60 kHz group; B: 60-108 kHz group; C: 108-156 kHz group;D: 156-204 kHz group; E: 204-252 kHz group.2 Fascicle IV.1 - Rec. M.390d02-scFIGURE 2/M.390.D022.1.2 Designation of channelsThe position occupied by a telephone channel of a carrier system is designated by means of a letter g
9、iving theposition of the group (transmitted on the line) containing the channel and by means of the number of the channel withinthis group.The designation of a channel on such a carrier system is therefore of the form A-7, C-9, D-4, etc. (i.e. group A,channel 7, etc.).2.2 Numbering in systems with i
10、nverted groupsIn this case, all the groups are in the same sense. For systems with five groups on symmetric pair cable, this isthe normal arrangement which is as shown in Scheme 2 of Figure 2/M.390 c).Fascicle IV.1 - Rec. M.390 32.2.1 Numbering of the groupsThe five groups, all in the same sense, ar
11、e numbered in the direction of ascending frequency, 5, 4, 3, 2, 1 andthe assembly constitutes a supergroup having a displacement by 48 kHz towards the lower frequencies of supergroup 1of 4-MHz coaxial system. For this reason the assembly of groups in the figure is designated by the number 1*, in ord
12、erto integrate this supergroup with the general numbering for supergroups.2.2.2 Numbering of channelsThe place occupied by a telephone channel in such a carrier system is also designated by three numbers,e.g. 1*-4 -11 (i.e. supergroup 1*, 12 channel group 4, channel 11).2.3 Systems with four groupsB
13、y agreement between the Administrations concerned, one group of supergroup 1* may be omitted, but theabove numbering of the groups and channels in the groups should be retained as if no group had been omittedsee scheme 1 bis of Figure 2/M.390 b).3 Systems providing two supergroups3.1 Alternative fre
14、quency arrangementsThe two recommended frequency arrangements are shown in scheme 3 and scheme 4 of Figure 3/M.390. Inscheme 4, the line-frequency allocation is the same as that for coaxial cable systems, and permits satisfactoryinterconnection at basic supergroup frequencies (312-552 kHz) between s
15、upergroups in these coaxial systems and thetwo supergroups on symmetric pair cable systems.d03-scFIGURE 3/M.390.D034 Fascicle IV.1 - Rec. M.390In scheme 3, the line-frequency allocation for supergroup 1* is the same as that recommended for a 5 groupsystem on symmetric pair cables scheme 2, Figure 2/
16、M.390 c).The frequency allocation shown for supergroup 1* in scheme 3 bis may be used by agreement betweenAdministrations where interconnection with existing systems having five groups or less is required.3.2 Numbering of supergroups, groups and channels3.2.1 The numbering of the groups and channels
17、 on a 2 supergroup system follows the principles given inRecommendations M.320 and M.330.3.2.2 For supergroup 2 in each scheme and for supergroup 1 in scheme 4 the numbering used is that given inRecommendations M.320 and M.330 for coaxial systems.3.2.3 For supergroup 1* and l* the numbering used is the same as that shown for scheme 2 and scheme 2 bis inFigure 2/M.390 c).
