1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G0,%!3%$G0G0#)2#5)43#(!2!#4%2)34)#3G0G0/&G0G0/2$).!2915!,)49G0G0).4%2.!4)/.!,G0G0,%!3%$#)2#5)43G0G0&/2-).G0G00!24G0G0/&02)6!4%G0G037)4#(%$G0G04%,%0(/.%.%47/2+3)45G134G0G0Recommendat
2、ionG0G0- (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation M.1030 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 ident
3、ical to the Blue Book version and 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 th
4、is publication may be reproduced 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.1030 1Recommendation M.1030Fascicle IV.2 - Rec. M.1030CHARACTERISTICS OF ORDINARY QUALITY INTERNA
5、TIONALLEASED CIRCUITS FORMING PART OF PRIVATESWITCHED TELEPHONE NETWORKS1 General1.1 ScopeThis Recommendation details the characteristics of an international leased circuit intended to form part of aprivate switched telephone network. The requirements of this Recommendation are intended to ensure th
6、e provision of acircuit suitable for telephony purposes. Such circuits may be used either singly, and thus provide for speechcommunication between two private telephone exchanges in different countries, or as part of a connection within aprivate switched telephone network covering two or more countr
7、ies.It should be noted that not all Administrations provide circuits of the type covered by this Recommendation.Recommendation G.171 1 contains the transmission planning considerations upon which the characteristicsgiven in 2 below are based, and specifies the maximum number of circuits in tandem wh
8、ich the transmission planpermits1).1.2 Terminology1.2.1 Circuit access pointsThe term “circuit access points” is used in this Recommendation with the same meaning as that given inRecommendation M.565 2. The precise location of, and relative levels at, the circuit access points are determined bythe i
9、nvolved Administrations in collaboration with the renter concerned.1.2.2 Four-wire circuitsThis term is intended to cover circuits which are switched on a 4-wire basis, are available via 4-wire circuitaccess points, and do not contain 2-wire circuit sections.1.2.3 Two-wire presented circuitsThis ter
10、m is used to cover circuits which do not meet the criteria set out in 1.2.2 above, for example, circuitsbetween exchanges using 2-wire switching.2 Characteristics2.1 Nominal overall lossIt is not possible to specify the nominal overall loss between actual switching points, or between circuit accessp
11、oints, because of the freedom afforded Administrations in choosing the relative transmission level at these points.In order to ensure satisfactory loss and stability performance on end-to-end connections within privateswitched networks, the overall loss of interconnecting international leased circui
12、ts may need to be the subject of bilateraldiscussion between the terminal Administrations. In this connection, see also 3 below.2.2 Loss/frequency distortionThe limits for overall loss relative to that at 1020 Hz are given in Figure 1/M.1030 and Figure 2/M.1030 for 4-wire and 2-wire presented circui
13、ts respectively. It may be noted that the limits in Figure 2/M.1030 are the same as thoseappearing in Recommendation M.1040, 2.2._1)Recommendation G.171, 1 1 states that for connection between private telephone networks and the public network, whenpermitted, “assurance cannot always be given that tr
14、ansmission performance to CCITT standards will be obtained.” The same maybe said for connections achieved by a user over which an Administration has no control, for example, between two or more privatenetworks by virtue of user provided private automatic branch exchanges (PABXs).2 Fascicle IV.2 - Re
15、c. M.1030Exceptionally, where a 2-wire private telephone exchange originates and terminates traffic in an otherwise4-wire network, the 4-wire section of an international leased circuit terminated on that exchange should meet therequirements of Figure 1/M.1030.d01-scFIGURE 1/M.1030.D01d02-scFIGURE 2/
16、M.1030.D02Fascicle IV.2 - Rec. M.1030 32.3 Variations of overall loss with timeFor all circuits, variation with time of the overall loss at 1020 Hz (including daily and seasonal variations butexcluding amplitude hits) should be as small as possible but should not exceed 4 dB.2.4 Random circuit noise
17、The nominal level of psophometric noise power depends upon the actual constitution of the circuit, inparticular upon the length of circuit of frequency division multiplex systems involved. The provisional limit for circuitsof lengths greater than 10 000 km is 38 dBm0p. However, circuits of shorter l
18、ength will have substantially less randomnoise (see Annex A to this Recommendation and Recommendation M.1050, 3.5).2.5 EchoThe provisions of Recommendations G.122 3 and G.131 4 concerning echo control should be observed inso far as they are applicable.3 StabilityNational systems interfacing with the
19、 international leased circuits dealt with in this Recommendation shouldcomply with the stability requirements of Recommendation G.122 3.Recognizing that national private switched networks (planned in accordance with national transmissionstandards) may ultimately be interconnected by international le
20、ased circuits, involved Administrations may need todiscuss the actions necessary to ensure adequate stability of the resulting international private switched network.ANNEX A(to Recommendation M.1030)Random circuit noiseFigure A-1/M.1030 displays random noise versus length of circuit of FDM carrier s
21、ystems and is presented asa guide to the random noise performance which may be found on an international leased circuit.d03-scFIGURE A-1/M.1030.D034 Fascicle IV.2 - Rec. M.1030Note At the present time the section of the circuit provided by satellite (between earth stations) employingFDM techniques c
22、ontributes approximately 10 000 pW0p (50 dBm0p) of noise. Therefore, for the purpose ofdetermining maintenance limits for noise measurement on leased circuits, the length of the section provided by satellitemay be considered to be equivalent to 1000 km in Figure A-1/M.1030.The contribution to noise
23、of a circuit section provided by satellite employing TDM techniques remains as asubject for further study.References1 CCITT Recommendation Transmission plan aspects of private operated networks, Vol. III, Rec. G.171.2 CCITT Recommendation Access points for international telephone circuits, Vol. IV, Rec. M.565.3 CCITT Recommendation Influence of national systems on stability, talker echo and listener echo ininternational connections, Vol. III, Rec. G.122.4 CCITT Recommendation Stability and echo, Vol. III, Rec. G.131.
