1、INTERNATIONAL TELECOMMUNICATION UNIONITU-T I.252.1TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU(11/88)SERIES I: INTEGRATED SERVICES DIGITALNETWORKService capabilities Supplementary services in ISDNCall offering supplementary services:Call TransferITU-T Recommendation I.252.1(Extract from the Blue Bo
2、ok )NOTES1 ITU-T Recommendation I.252.1 was published in Fascicle III.7 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 an
3、d 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, 1999All rights reserved. No part of this publication may be reproduced
4、 or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.7 Rec. I.252.1 1Recommendation I.252.1Fascicle III.7 Rec. I.252.1CALL OFFERING SUPPLEMENTARY SERVICES:CALL TRANSFER (CT)(Melbourne, 1988)In
5、troductionThe purpose of this Recommendation is to provide the stage 1 description of the method defined inRecommendation I.130 using the means given in Recommendation I.210.Supplementary services are described by a prose definition and description (step 1.1) and by a dynamicdescription (step 1.3).
6、The application of the attribute technique (step 1.2), as defined in Recommendation I.140, forsupplementary services is for further study.This Recommendation describes the following Call Offering supplementary services:I.252.1 Call Transfer (CT)I.252.2 Call Forwarding Busy (CFB)I.252.3 Call Forwardi
7、ng No Reply (CFNR)I.252.4 Call Forwarding Unconditional (CFU)I.252.5 Call Deflection (CD) (Note)I.252.6 Line Hunting (LH)Note This service having been identified now requires further study; its description is not yet included.1 I.252.1 Call Transfer1.1 DefinitionThe Call Transfer supplementary servi
8、ce enables a user to transfer an established (i.e. active) call to a thirdparty. For the original call, the “served user” (see 1.2.2) may have been either the calling or called party (i.e. the callmay have been either incoming or outgoing). This service differs from the Call Diversion (i.e. Call For
9、warding)supplementary services in that the latter deal only with incoming calls that have not yet reached the “fully-established”state, whereas in the case of Call Transfer an established end-to-end connection exists.1.2 Description1.2.1 General descriptionThree methods of Call Transfer are identifi
10、ed. One, called “Normal” Call Transfer, is described in 1.3.2below. The two others are described in 1.3.4. Although the invocation of these various methods differ, the essentialoperation of Call Transfer is to transform the served users established call into a new call between the other party on the
11、established call and a third party. It should be noted that, in a Three-Party Service call, there are several stages at whichthe served user can effectively transfer the call. These are described in the Three-Party Service description.1.2.2 Specific terminology1.2.2.1 Served user, other partiesDurin
12、g the invocation and active phases, the service is under the control of the “served user”, i.e. the one forwhom the service was subscribed. This user is also referred to as “user A”. Other parties associated with this service aredefined as follows: user B is the other party in the original call (A B
13、); user C is the “third party” the other party in the subsequent call (A fi C).2 Fascicle III.7 Rec. I.252.11.2.3 Qualifications on the applicability to telecommunication servicesThis supplementary service is considered meaningful when applied to the Telephony teleservice and thespeech and 3.1 kHz a
14、udio bearer service. Furthermore, it may also be meaningful when applied to other services.1.3 Procedures1.3.1 Provision/withdrawalThe Call Transfer supplementary service is subscribed to by prior arrangements with the service provider.Subscription can be made for “Normal Call Transfer” and/or for e
15、ither of the alternate procedures (i.e. “Single-Step CallTransfer” or “Explicit Call Transfer”) offered by the service provider.Withdrawal of the service is made by the service provider upon request by the subscriber or for serviceprovider reasons.1.3.2 Normal procedures1.3.2.1 Activation/deactivati
16、on/registrationNone identified.1.3.2.2 Invocation and operationThe served user, user A, can transform an established call with user B into (effectively) a call from user B to athird party, user C. When the served user (user A) asks the service provider to begin the “Normal” Call Transfer, theservice
17、 provider puts the already established call (with user B) on hold. User A then proceeds to establish the second call(to user C). Upon request from user A to complete the Call Transfer, the service provider would connect users B and Ctogether while removing the connections between user A and the othe
18、r two users. (The extent to which the serviceprovider re-uses the resources from the A B and A fi C calls to form the B fi C call is a service provider option.)Note In the resulting call B fi C, user C will have all the relevant characteristics of the called party, butuser B will not necessarily hav
19、e all the characteristics of the calling party, depending on whether user B called user Aand also depending on which service or supplementary service is under consideration.In some networks, user A can request completion of the Call Transfer either during or after the establishmentof the connection
20、to user C.The service provider will optionally notify users B and C of the transfer and, depending on interworkingconditions and the supplementary services subscribed to by users B and C, will indicate to user B the number of user Cand will indicate to user C the number of user B.1.3.3 Exceptional p
21、rocedures1.3.3.1 Activation/deactivation/registrationNone identified.1.3.3.2 Invocation and operationThe service request would be rejected if the user invoking the service has not subscribed to the Call Transferservice (or the requested service option). The user would be notified of the cause for re
22、jection and the original callA B would remain in the state it was in before the transfer request was received.If user As attempt to establish a connection to user C is unsuccessful, (e.g. user C is busy), user A will be soinformed and will be able either to retrieve the original call A B or to attem
23、pt a new connection (e.g. to C or toanother party) (see Figure 3/I.252).The transfer request would be rejected if the network is unsuccessful in connecting users B and C (e.g. whenuser C is busy, when there is network congestion, or when transfer restrictions are violated). The user would be notifie
24、dof the cause for rejection and the two calls would remain in the states they were in before the request was received.Fascicle III.7 Rec. I.252.1 31.3.4 Alternative procedures1.3.4.1 Activation/deactivation/registrationNone identified.1.3.4.2 Invocation and operation1.3.4.2.1 Single-Step Call Transf
25、erIn this procedure, the served user can transfer an established call (with user B) to another user (user C) withoutfirst establishing a call to user C. When invoking a Single-Step Call Transfer, the served user would indicate to theservice provider the address of user C. The service provider would
26、then establish a connection between users B and C,and disconnect the served user, user A, from the original call with user B. It should be noted that the service provider isnot required to reinstate the call A B if a Single-Step Call Transfer to user C fails. It is also necessary to notify user Bof
27、the progress of the establishment of the call to user C, particularly if the call A B cannot be reinstated.1.3.4.2.2 Explicit Call TransferIn this procedure, the served user A puts the already established call (with user B) on hold and then proceedsto establish another call (to user C) or to accept
28、an incoming call (from user C). If user As attempt to establish aconnection to user C is unsuccessful (e.g. user C is busy), user A will be so informed and will be able either to retrievethe original call A B or to attempt a new connection (e.g. to user C or to another party) (see Figure 4/I.252).Us
29、er A then explicitly requests that the call with user B be transferred to user C. By contrast, in the NormalCall Transfer procedure, the service provider “knows” that the two calls (A B and A fi C) are related; requestingcompletion of Normal Call Transfer for call A fi C implicitly means “connect us
30、er C with user B”. The remainder ofthe procedures are identical to Normal Call Transfer (with the possible exception of the failure procedures.)1.4 Network capabilities for chargingThis Recommendation does not cover charging principles. Future Recommendations in the D-Series areexpected to contain t
31、hat information.It shall be possible to charge the subscriber accurately for the service.1.5 Interworking requirementsUser B and user C may not be able to receive each others address if one (or both) of the calls exits from theISDN network. The different scenarios are shown in the following tables.
32、The tables assume that B is the originator ofthe call to A. The network may not be able to recognize user identification if one or both of the calls requiresinterworking with non-ISDN network(s).For illustrative purposes, assume that user B originates a call to user A, and user A initiates the call
33、transferservice to connect user B to user C. The different scenarios are shown in the following tables:i) Users A, B and C are in ISDNAddress informationavailable toAddress of A Address of B Address of CUser A YES YESUser B YES YESUser C YES YES 4 Fascicle III.7 Rec. I.252.1ii) Users A and B are in
34、ISDN. User C is in another networkiii) Users A and C are in ISDN. User B is in another networkiv) User A is in ISDN. Users B and C are in another network1.6 Interaction with other supplementary services1.6.1 Call WaitingAssume served user A has an established call with user B and wishes to transfer
35、user B to user C, and users A,B and C all have subscribed to the Call Waiting Service. If a call from user D is received while:i) user A is invoking Normal Call Transfer If user D calls user A at any time before A requests the completion of the transfer of user B touser C, then user A shall receive
36、a call waiting indication. When user B is transferred to user C, aB-channel would normally become idle, enabling user A to accept the waiting call. If user D calls user B, then user B can use normal call waiting procedures to accept the waiting call(preferably once the transfer to user C is complete
37、d). If user B had a call waiting indication while thecall was established with user A, the call waiting indication shall not be affected by the transfer ofuser B to user C. If user D calls user C during the transfer process (i.e. while user C is engaged on an active call withuser A), the call waitin
38、g indication shall be presented to user C. User C could then use Normal CallWaiting procedures to accept the waiting call (preferably once the call transfer is completed).Address informationavailable toAddress of A Address of B Address of CUser A YES YESUser B YES YESUser C NO NO Address information
39、available toAddress of A Address of B Address of CUser A NO YESUser B YES NOUser C YES NO Address informationavailable toAddress of A Address of B Address of CUser A NO YESUser B YES NOUser C NO NO Fascicle III.7 Rec. I.252.1 5ii) user A is invoking Single-Step Call Transfer User A may receive a cal
40、l waiting indication any time before or during the transfer invocation. Oncethe Single-Step Call Transfer is invoked, then user A is disconnected from user B, thus, causing aB-channel to normally become idle, enabling user A to accept the waiting call. User B may receive a call waiting indication an
41、y time before or during the transfer invocation.User B could then use Normal Call Waiting procedures to accept the waiting call (preferably oncethe transfer is completed). If the transfer is not successful (e.g. user C is busy), then user B wouldnormally release the call, causing a B-channel to beco
42、me idle and enabling user B to accept thewaiting call. If the call from user D arrives at user Cs serving office after the call from A, user C would receive acall waiting indication. The call waiting indication shall not be affected by the transfer of user B touser C. User C could then use Normal Ca
43、ll Waiting procedures to accept the waiting call (preferablyonce the transfer is completed). If the call from user D arrives before the call from user A, the callfrom user A will receive call waiting treatment.iii) user A is invoking Explicit Call Transfer The interaction for users A, B, or C with c
44、all waiting are the same as for i) above.1.6.2 Call TransferIt shall be possible for both users (user A and user B) in a normal call, who have each subscribed to the CallTransfer Service, to simultaneously transfer the call. That is, if user A and user B are active in an established call, user Acoul
45、d transfer the call to a user C and user B could transfer the call to a user D. Call progress signals and othernotifications will be delivered to the appropriate party at the time the signal is received. See Figure 1/I.252.D01DBCAFIGURE 1/I.252FIGURE 1/I.252.D011.6.3 Connected Line Identification Pr
46、esentation (COLP)Assume that user A has an established call with user B and wishes to transfer this call with user B to user C.Except in the case where user C prohibits the presentation of his/her number, user Cs number shall be presented: to user B upon the successful completion of the transfer to
47、user C (independent of the type of transferprocedure invoked by user A) provided that user B has subscribed to COLP; to user A when user A is using the Normal or Explicit Call Transfer procedures and has subscribed toCOLP. The reached partys number will not be presented to user A if user A invokes t
48、he Single-Step CallTransfer procedure.Note Number presentation may not be possible if interworking with a non-ISDN network is involved in thecall transfer.1.6.4 Connected Line Identification Restriction (COLR)Assume that a user A has an established call with a user B and wishes to transfer this call
49、 with user B to auser C.If user C has subscribed to COLR, then user A shall not receive user Cs number when user A invokes anyCall Transfer procedure and user B shall not receive user Cs number during the transfer of user B to user C.6 Fascicle III.7 Rec. I.252.11.6.5 Calling Line Identification Presentation (CLIP)For Normal and Explicit Call Transfers, user A shall have his number presented to user C and user B shallhave his number presented to user C unless:1) user A or B has number presentation res
