1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G02%#/-%.$!4)/.3G0G0/.G0G04%,%0(/.%37)4#().G0G0!.$G0G03).!,).).4%2.!4)/.!,G0G0!54/-!4)#G0G0!.$3%-)G13!54/-!4)#G0G07/2+).$%-!.$G0G0!33).-%.4G0G03).!,).3934%-3)45G134G0G0RecommendationG0G01 (Extract fro
2、m the “LUEG0“OOK)NOTES1 ITU-T Recommendation Q.48 was published in Fascicle VI.1 of the Blue Book. This file is an extract from theBlue 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 v
3、ersion 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 this publication may be r
4、eproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle VI.1 - Rec. Q.48 1Recommendation Q.48Fascicle VI.1 - Rec. Q.48DEMAND ASSIGNMENT SIGNALLING SYSTEMS1)1 The term “demand assignment“ (ab
5、breviated as DA) should be taken as meaning that the assignment is on aper-call basis.Note - Satellite circuits with demand assigned multiple access are those circuits which may be set up byassignment of a satellite link to operate between specified earth stations when the actual demand arises.The o
6、rigin, destination, or both of the satellite link can be varied. The link is assigned to set up the requiredtelephone circuit according to the call.This defines the following concepts:1) variable destination satellite link;2) variable origin satellite link;3) fully variable satellite link (the origi
7、n and destination of which may both be varied).The Recommendation covers, when applicable, fully variable and variable destination types of DA systems.2 The DA signalling system shall be capable of interworking with all currently standardized CCITT signallingsystems and shall have the capacity to ca
8、rry all the telephony signals currently provided by these CCITT signallingsystems and shall in addition provide reserve capacity.Any currently standardized CCITT signalling system shall be able to be applied to any access link. DifferentCCITT signalling systems may be applied to the various access l
9、inks at the same time.3 Account should be taken of the fact that particular earth stations may have special signalling requirements tosuit the CTs using these earth stations (e.g. joint use of an earth station by a number of CTs, long distances between CTand earth station, CTs with access to more th
10、an one earth station).4 The DA signalling system shall be an integrated signalling system used both for:a) signalling for setting up the DA speech circuit; andb) transfer of the information flow for telephony.5 The DA signalling system shall be capable of transmitting address information in both the
11、 en bloc and theoverlap mode of operation. The transmission of address information by the outgoing DA system terminal should besuch as to result in minimum delay to these signals in the DA system.The manner of transmitting signals over the DA signalling system shall be independent of the type ofsign
12、alling system to be encountered in the access link at the far end.Accordingly, the interworking arrangements described in Table 1/Q.48 are recommended. (For definitions of“en bloc“ and “en bloc overlap“ see the definitions in Recommendation Q.151 2.)_1)See also the reference cited in 1.2 Fascicle VI
13、.1 - Rec. Q.486 The DA signalling system shall send out address digits from ESBto CTBin the correct order, that is, theorder of dialling.7 Means shall be provided for preventing spillover of signals between successive calls, which use the samesatellite channel through the DA signalling system.8 The
14、DA signalling system should be capable, for the sequence re-answer signal-clear back signal ofcorrectly extending to CTAfrom ESA, the last state representing the final position of the called partys switch hook.9 The message structure of the demand assignment signalling system should be such that one
15、 message willcontain all the information necessary for one event (e.g. answer signal for one particular circuit). Single unit and multi-unit messages should be catered for. Each signal unit should contain both information and check bits.10 All time-outs for both normal and abnormal conditions in the
16、 DA signalling system should be designedaccording to the recommendations concerning the relevant CCITT signalling systems.11 Signal transfer time through the DA signalling system should be fast. While no firm time requirements inregard to the various components of signal transfer time have been esta
17、blished, design objectives in terms of averageand 95% level values for the signal transfer time (Td) for answer signals, other one-unit messages and the initialaddress message are given. These figures are to be viewed as reasonable objectives and not as firm requirements.11.1 Signal transfer time in
18、 the DA signalling systemA signal transfer time in the DA signalling system is specified. This signal transfer time is called Tdin thediagram of Figure l/Q.48.Fascicle VI.1 - Rec. Q.48 3The value Td= Td- Tpshould be used as the design objective for the DA signalling system. The values of Tdcalculate
19、d for the design of the system are shown in Table 2/Q.48.Note - These figures have to be interpreted as reasonable estimates and not as firm requirements.TABLE 2/Q.48Values of signal transfer times for design of a DA signalling systemDesign objectives for TdTd= Td- TpType of message Answer Other one
20、-unit message IAM of 5 SUTdin ms AV 52 85 14595% level 85 175 235For calculation use the following relations:For basis of calculation see 4.4 Fascicle VI.1 - Rec. Q.4812 Dependability requirementsThe requirements specified for System No. 6 (see 5) are recommended as the objectives for the DAsignalli
21、ng system.12.1 Signal transfer dependability (see 6)“b) Signal units of any type which give rise to wrongly accepted signals due to undetected errors and causingfalse operation (e.g. false clear-back signal):not more than one error in 108of all signal units transmitted, andc) As in item b) but causi
22、ng serious false operation (e.g., false metering or false clearing of a connection):not more than one error in 1010of all signal units transmitted.“12.2 Error correction by retransmission (see 7)Although the bit error rate in the DA signalling system has not been determined, the design of the system
23、should be made such that a design objective “not more than one in 104signal units carrying telephone information isallowed to be delayed as a consequence of error correction by retransmission.“12.3 Interruption of the signalling service (see 8)System No. 6 requirements are:- interruption of duration
24、 between 2 seconds and 2 minutes: not more than once a year;- interruption of duration exceeding 2 minutes: not more than once in 10 years.Since the speech circuits and the signalling channel in the DA system normally will be interruptedsimultaneously, it is understood that the above figures are rel
25、ated to the signalling equipment and not to thetransmission media common to both the signalling channel and the speech circuits.References1 Signalling for demand assignment satellite systems, Green Book, Vol. VI-4, Supplement No. 8, ITU, Geneva,1973.2 CCITT Recommendation Signal code for register si
26、gnalling, Vol. VI, Rec. Q.151.3 CCITT Recommendation Signal transfer time definitions, Vol. VI, Rec. Q.252.4 CCITT Recommendation Signal transfer time requirements, Vol. VI, Rec. Q.287, Annex A.5 CCITT Recommendation Service dependability, Vol. VI, Rec. Q.276, 6.6.1.6 Ibid., 6.6.1, b) and c).7 Ibid., 6.6.1, a).8 Ibid., 6.6.1, d).
