ITU-T U 41-1988 CHANGED ADDRESS INTERCEPTION AND CALL REDIRECTION IN THE TELEX SERVICE《用户电报业务中的改址栏截和呼叫改发》.pdf

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1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 5 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(G0G037)4#().0!24)#5,!2G0G03).!,).G0G0 amended at Melbourne, 1988)DefinitionsFor the purpose of this Recommendation the following definitions shall apply: Subscriber A is the calling subscriber; Subscr

2、iber B is the redirecting subscriber; Subscriber C is the subscriber to which the call shall be redirected.The CCITT,considering(a) that, with fully automatic working between telex subscribers, it is desirable to envisage the possibility of: a fully automatic changed address interception facility, a

3、 fully automatic call redirection facility;(b) that the operation of such facilities has an influence upon telex calls originated by other Administrationsand therefore requires international standardization;(c) that operation in networks employing signalling systems according to Recommendations U.1,

4、 U.11 andU.12 must be considered;(d) that the described facilities in the called network must be compatible with existing call setup procedures inthe originating and transit network(s),unanimously declares the following view1 Changed address interception1.1 In existing networks, in the case of a cal

5、l to a subscriber whose number has been changed, the incomingnetwork may return the service code NCH. The service signal is not preceded by the call connected signal. It is alwaysfollowed by the clearing signal in accordance with Recommendation F.60 1, U.l ( 10.1 and Table 1b/U.1) and U.11(Table 1/U

6、.11).1.2 In new networks and as far as possible in existing networks, it would be desirable to inform the callingsubscriber of the new number to be selected by means of a suitable sequence of signals, which should have thefollowing format: NCH :xx (where xx represents the figures of the new number),

7、followed by the clearing signal. This sequence must be preceded by the call-connected signal. A pause of at least twoseconds must be provided between the beginning of the call connected signal and the beginning of the NCH servicesequence defined above. Every step should be taken to ensure that the p

8、eriod between the call-connected signal and theclearing signal does not exceed 5 seconds, in order to avoid accounting in accordance with Recommendations U.1 andF.61 2.2 Fascicle VII.2 - Rec. U.411.3 Operating Administrations may optionally offer automatic redirection to the new number of a call to

9、one oftheir subscribers whose number has been changed. This redirection will be in accordance with 2 below, and thesequence “RDI” as specified under 2.1 below shall then apply. Under no circumstances shall the NCH sequence bepreceded by the RDI service sequence. This supplementary service shall be a

10、vailable for a limited period only. It maynot be offered beyond the time during which the Administration informs calling subscribers of the change in the callnumber.2 Call redirection2.1 In new networks and as far as possible in existing networks, a call redirection should be signalled by the return

11、to the calling station of a sequence of signals constituted by the code expression RDI followed by the indication of thenew number to which the call is redirected, in accordance with the following format: RDI :xx (where xx represents the figures of the new number),followed if necessary by further le

12、tter-shifts (); the total number of characters in the sequence may in no case exceed20.Failing this, at least the code expression RDI, as specified in Recommendations U.1 and F.60, without anyfurther indication, should be returned.2.2 The call redirection sequences specified in 2.1 above must always

13、 follow the call connected signal. A periodof two seconds must elapse between the beginning of the call connected signal and the beginning of the RDI sequence.The answerback of the Subscriber C will then be returned to the Subscriber A in accordance with the proceduresoutlined in Recommendation U.1,

14、 7. (It should be noted that there are networks which return the RDI-sequence afterthe answerback sequence and in addition to the NCH and new call number.)2.3 Administrations offering call redirection facilities should take all necessary technical and administrative stepsto ensure that the same call

15、 can in no circumstances give rise to more than one redirection and that the total number ofcircuits used to establish the call after redirection does not exceed the maximum tolerated in the transmission plan forthe national network.2.4 With regard to the call redirection facility, redirection shoul

16、d not take place to addresses outside the jurisdictionof the Administration performing the redirection function, therefore the new address shall consist only of the nationalnumber.2.5 Interworking between automatic terminals, Teletex to telex conversion facility and other services in theoriginating network and a redirected subscriber station in a terminating network is for further study.References1 CCITT Recommendation Operational provisions for the international telex service, Rec. F.60.2 CCITT Recommendation The chargeable duration of a telex call, Rec. F.61.