1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU 1.252.7 (05/97) SERIES I: INTEGRATED SERVICES DIGITAL NETWORK Service capabilities - Supplementary services in ISDN Call offering supplementary services: Explicit call transfer ITU-T Recommendation I .252.7 (
2、Previously CCIlT Recommendation) ITU-T I-SERES RECOMMENDATIONS INTEGRATED SERVICES DIGITAL NETWORK GENERAL STRUCTURE Terminology Description of ISDNs General modelling methods Telecommunication network and service attributes General description of asynchronous transfer mode Scope General aspects of
3、services in ISDN Common aspects of services in the ISDN Bearer services supported by an ISDN SERVICE CAPABILITIES OVERALL NETWORK ASPECTS AND FUNCTIONS Network functional principles Reference models Numbering, addressing and routing Connection types Performance objectives Protocol layer requirements
4、 General network requirements and functions ISDN USER-NETWORK INTERFACES Application of I-series Recommendations to ISDN user-network interfaces Layer 1 Recommendations Layer 2 Recommendations Layer 3 Recommendations Multiplexing, rate adaption and support of existing interfaces Aspects of ISDN affe
5、cting terminal requirements INTERNETWORK INTERFACES MAINTENANCE PRINCIPLES B-ISDN EQUIPMENT ASPECTS ATM equipment Management of ATM equipment 1.100-1.199 I. 1 l-I. 1 19 1.120-1.129 I. 130-1.139 I. 140-1.149 I. 150-1.199 1.200-1.299 I .200-1.209 1.210-1.219 1.220-1.229 1.2361.239 1.240-1.249 1.300-1.
6、399 1.310-1.319 1.320-1.329 1.330-1.339 1.340-1.349 1.350-1.359 I.3-1.369 1.370-1.399 1.400-1.499 1.420-1.429 1.430-1.439 1.440-1.449 1.450-1.459 1.460-1.469 1.470-1.499 1.500-1.599 1.600-1.699 1.700-1.799 1.730-1.749 1.750-1.799 For further details, please refer to ITU-T List of Recommendations. IT
7、U-T RECOMMENDATION 1252.7 CALL OFFERING SUPPLEMENTARY SERVICES: EXPLICIT CALL TRANSFER Summary Two methods of call transfer are identified. The explicit call transfer supplementary service is described in this Recommendation. The other is described in Recommendation 1.252.1. The explicit call transf
8、er supplementary service enables a user to transform two of that users calls, each of which can be an incoming or an outgoing call, into a new call between the other parties in the two calls. Prior to transfer, one of the two calls shall be answered, the other call can be either alerting or answered
9、, depending on a network option. Calls incoming to the served user must have been answered. Source ITU-T Recommendation 1.252.7 was prepared by ITU-T Study Group 2 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 26th of May 1997. Recommendation 1.252.7 (05/97) i - STD-I
10、TU-T RECMN 1=252-7-ENGL 1797 lrBb259L ObiOlr27 Alb FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommuni- cations. The ITU Telecommunication Standardization Sector (IT-T) is a permanent organ of the ITU. The ITU-T is responsible for
11、 studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Stu
12、dy Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. In some areas of information technology which fall within IT-Ts purview, the necessary standards are pr
13、epared on a collaborative basis with IS0 and EC. I NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS The IT draws attention to the possibility that t
14、he practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The IT takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by TT members or others outside of the Recommendati
15、on development process. As of the date of approval of this Recommendation, the ITU hadhad not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information
16、 and are therefore strongly urged to consult the TSB patent database. O ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITLJ. 11
17、 Recommendation 1.252.7 (05/97) 1 2 3 4 5 6 CONTENTS Definition . Description . 2.2 Specific terminology . 2.3 Qualifications on the applicability to telecommunication services . Procedures 3.1 Provisiodwithdraw al 2.1 General description . 3.2 Normal procedures 3.3 Exceptional procedures . Network
18、capabilities for charging Interworking requirements . 5.1 Interworking with non-ISDNs Interworking with private ISDNs . 3.4 Alternative procedures 5.2 Interaction with other supplementary services . 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20 6.21 6.22
19、6.23 Advice of charge services . Call Hold (HOLD) Call transfer services . Call Waiting (CW) Closed User Group (CUG) . Completion of calls services . Conference services Diversion services . Direct-Dialling-In (DDI) In-call Modification (IM) . Line Hunting (LH) ISDN Freephone Service (IFS) . Malicio
20、us Call Identification (MCID) Multi-Level Precedence and Preemption (MLPP) Multiple Subscriber Number (MSN) Name identification services . Number identification services . Outgoing Call Barring (OCB) Reverse charging (REV) . Sub-addressing (SUB) Support of Pnvate Numbering Plans (SPNP) . Page 1 1 1
21、1 1 2 2 2 3 3 3 3 4 4 4 4 5 5 6 6 6 6 6 7 7 7 7 7 7 8 8 8 8 8 8 8 Terminal Portability (TF) 9 User-to-User Signalling (WS) 9 7 Dynamic description 9 Recommendation 1.252.7 (05/97) iii Recommendation 1.252.7 CALL OFFERING SUPPLEMENTARY SERVICES: EXPLICIT CALL TRANSFER (Geneva, 1997) 1 Definition Expl
22、icit Call Transfer is an ISDN supplementary service which enables a user who has two calls, each of which can be an incoming or an outgoing call, to connect the other parties in the two calls. 2 Description 2.1 General description Two methods of call transfer are identified. The Explicit Call Transf
23、er (ECT) supplementary service is described below. The other is described in Recommendation 1.252.1. The Explicit Call Transfer supplementary service enables a user to transform two of that users calls, each of which can be an incoming or an outgoing call, into a new call between the other parties i
24、n the two calls. Prior to transfer, one of the two calls shall be answered, the other call can be either alerting or answered, depending on a network option. Calls incoming to the served user must have been answered. 2.2 Specific terminology This Recommendation defines the following terms: 2.2.1 sup
25、plementary service. This user is also referred to as “user A“. served user, other parties: The served user is the user who subscribes to and invokes the explicit call transfer The other parties associated with the explicit call transfer supplementary service are defined as follows: - user B is the o
26、ther party in one (the answered) call; - user C is the other party in the second call. This user can also be referred to as “the third party“. 2.2.2 Recommendation 1.253.2) is currently in operation. held call, call not held: A held call is a call on which the call hold supplementary service (see A
27、call which is not held is a call on which the call hold supplementary service is not currently in operation. 2.2.3 Recommendations 1.23 1 and 1.241). answered call, alerting call: An answered call is a call on which the connection has been established (see An alerting call is a call on which the cal
28、led user is being informed of the call (see Recommendations 1.231 and I.241), but the connection has not yet been established. 2.3 Qualifications on the applicability to telecommunication services The explicit call transfer supplementary service is applicable to all circuit-switched basic telecommun
29、ications services. Recommendation 1.252.7 (05/97) 1 3 Procedures 3.1 Provisiodwithdrawal The explicit call transfer supplementary service is subscribed to by prior arrangements with the service provider. Subscription to the other call transfer services (Le. Single-Step Call Transfer and Normal Call
30、Transfer) can be included in this subscription or may be offered independently by the service provider. Withdrawal of the explicit call transfer supplementary service is made by the service provider upon request by the subscriber or for service provider reasons. 3.2 Normal procedures 3.2.1 Activatio
31、nideactivatiodregistration None identified. 3.2.2 Invocation and operation The served user (user A) who has two calls (with user B and user C), each of which can be an incoming or an outgoing call, can request the invocation of the explicit call transfer supplementary service with respect to the two
32、 calls. Prior to requesting the invocation of the explicit call transfer supplementary service, the following conditions apply: - one of the calls (referred to as the call between user A and user B) shall have been answered; - the call between user A and user C shall have been answered, or as a serv
33、ice provider option, this call can be alerting at user C; and at most one of the calls shall be on hold. - NOTE 1 -It is the responsibility of the served user to ensure that the two calls are compatible. NOTE 2 - At most one of the calls may be on hold, but it is not relevant which call (between use
34、r A and user B or between user A and user C) is on hold when the explicit call transfer supplementary service is invoked. For example, a user who has an answered call can put that call on hold and then set up a second call. After that, the served user can interchange the held and not held states of
35、the two calls as appropriate. On successful invocation of the explicit call transfer supplementary service, the two calls between user A and user B and between user A and user C respectively, shall be removed from user As access and shall be transformed into a call between user B and user C. If user
36、 C is being informed of the call at the time of transfer, user C shall continue to be informed of the call, and on answer shall be connected to user B. The service provider will optionally notify users B and C of the transfer and shall indicate to user B the answered or alerting state of the third p
37、arty (user C). In the case where a network supports the service provider option in the second paragraph above, then after the transferred alerting call is answered, user B shall again be notified in order to indicate the answered state. Subject to any restrictions (see 6.17.2 and 6.17.4), the ISDN n
38、umber of user B shall be indicated to user C. Subject to any restrictions (see 6.17.2 and 6.17.4), the ISDN number of user C shall be indicated to user B, either: - - at the time of transfer, if the call between user A and user C had been answered; or when user B is informed that user C has answered
39、 the call. if this occurs after transfer. After receiving the indication that the transfer has occurred, user B can provide a subaddress. If this information is supplied by user B, the network shall deliver it to user C, independently of any restrictions (see 6.17.2 and 6.17.4). If the call between
40、user A and user C has been answered, user C can also provide a subaddress after receiving the indication that transfer has occurred. If this information is supplied by user C, the network shall deliver it to user B independently of any restrictions (see 6.17.2 and 6.17.4). 2 Recommendation 1.252.7 (
41、0997) If user C answers the call after transfer has occurred and user C provides a subaddress, then user B shall be given the subaddress of user C subject to any restrictions (see 6.17.4) when user B is informed that the call has been answered by user C. NOTE - Users wishing to have their subaddress
42、 given to the other user will need to register their subaddress with their terminai in advance. 3.3 Exceptional procedures 3.3.1 Activatioddeactivation/registration None identified. 3.3.2 Invocation and operation The explicit call transfer supplementary service request would be rejected if the user
43、invoking the service has not subscribed to the explicit call transfer supplementary service. Also, the explicit cai1 transfer supplementary service request would be rejected if the network is unsuccessful in connecting user B and user C (e.g. when user C is busy, when there is network congestion, wh
44、en transfer restrictions are violated, if both calls to user B and user C are unanswered, or if both calls to user B and user C are on hold). User A would be notified of the cause for rejection and the two calls between user A and user B and user A and user C would remain in the states they were in
45、before the explicit call transfer supplementary service request was received. In an ISDN, the ECT supplementary service invocation will be rejected if it is detected that an uncontrolled connection would result. An uncontrolled connection is a sequence of ECT invocations that creates a connection in
46、 a network which is under no user control. The served user will be notified of the cause for rejection and existing calls will remain in the states they were in before the invocation of the ECT supplementary service. If the ISDN number of user B or user C cannot be given to the other user (e.g. due
47、to number presentation restriction, or number not available), when the indication that the transfer has occurred is given to the user, then the user who would have been given the ISDN number, may receive an indication of why no ISDN number is given. 3.4 Alternative procedures 3.4.1 Activatioddeactiv
48、atiodregistration None identified. 3.4.2 Invocation and operation None identified. 4 Network capabilities for charging This Recommendation does not cover charging principles. Future Recommendations in the D-Series are expected to contain that information. It shall be possible to charge the subscribe
49、r accurately for the service. 5 Interworking requirements In interworking with some networks, when user B and user C are both non-ISDN users, attached either to non-ISDNs or to private ISDNs, it may not be possible to detect the formation of an uncontrolled connection as the result of an invocation of the ECT supplementary service. In this case, the ECT may be rejected and, if so, the served user will be notified of the cause for rejection and existing calls will remain in the states they were in before the invocation of the ECT supplementary service. 3 Recommendation 1.2
