1、CCITT RECMN*I.252. 2 92 m Y862591 05738bb 707 m CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE INTERNATIONAL TELECOMMUNICATION UN ION 1.252.2 (08/92) INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES CALL FORWARDING BUSY Recommendation 1.25
2、2.2 Geneva, 1992 t _ - - - CCITT RECMN*I.252. 2 92 = 4862593 0573867 643 = FOREWORD The CCI“ (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff q
3、uestions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCITT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations b
4、y the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCIlT Resolution No. 2 (Melbourne, 1988). Recommendation 1.252.2 was revised by Study Group I and was approved under the Resolution No. 2 procedure on the 4th of August 1992. CCI“ NOTES 1) telecommunication Ad
5、ministration and a recognized private operating agency. 2) In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a A list of abbreviations used in this Recommendation can be found in Annex A. O ITU 1992 Ail rights reserved. No part of this publication may b
6、e reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. CCITT RECflN*I.252. 2 92 W 48b2591 0573868 58T W Recommendation 1.252.2 CALL FORWARDING BUSY (revised 1992) 1 Definition Call Forwarding B
7、usy Service permits a “served user” (see Q 2.2) to have the network send to another number all incoming calls for the served users ISDN number (or just those associated with a specified basic service) which meet busy at the served users ISDN number. The served users originating service is unaffected
8、. The forwarded-to number is registered with the network for use on all calls. Note - In normal situations, the service is provided on a per access basis. (In these situations, there is a one- to-one relationship between ISDN number and access.) However, the network may recognize multiple numbers on
9、 a single interface; in addition, it may not understand a complete ISDN number (e.g. Direct-Diallkg-In). In these cases, the Call Forwarding Busy service is offered on the basis of the part of the ISDN number which the network can recognize. 2 Description 2.1 General description For a given ISDN num
10、ber, the Cali Forwarding Busy (CFB) service (including options) may be subscribed to for each basic service to which the user) of the number subscribes, or collectively for all the basic services to which the user) subscribes. Since subscription is on an ISDN number basis, the same call forwarding s
11、ubscriptions will apply to ail terminais using this number. Note - In this service description, it is assumed that a single ISDN number is not shared across multiple interfaces. A single ISDN number may, however, be shared by multiple terminais on the same interface. Procedures permitting an ISDN nu
12、mber to be shared across multiple interfaces are for further study. For multiple access installations, it may be possible for the user to specify, on activation, if the service is applicable to a specific access or all accesses associated with that installation. The served user can request a differe
13、nt forwarded-to number for each basic service subscription parameter value to which he has subscribed. An indication that the CFB service is activated on a number may, as an option, be given to the user who has forwarding activated, each time an outgoing call is made. This may take the form of a spe
14、cial indication in the proceed response. 2.2 Specific terminology Served user: User of a particular ISDN number who is requesting that calls to his number be forwarded. This user may also be referred to as the forwarding user or the called user. Forwarded-to-user: User to whom the call shall be forw
15、arded. 2.3 Qualifications on the applicability to telecommunication services No restrictions identified. Recommendation 1,252.2 (08192) 1 3 3. _ _. _- - CCITT RECMN*I*252* 2 92 4862593 0573869 436 Procedures Provisiodwithdrawal CFB service shall be provided after pre-arrangement with the service pro
16、vider. The service can be offered with four subscription options. Options apply separately to each basic service subscribed to on each ISDN number. For each subscription option, only one value can be selected. Subscription options are summarized below: Subscription options Served user receives notif
17、ication that the call has been forwarded Calling user receives notification that the cail has been forwarded (see Note) Served user receives notification that CFB is currently activated Served user releases hisher number to forwarded-to user Value No Yes, with information about the call for the NDUB
18、 case (see 0 3.2.2) No Yes, without the forwarded-to user number Yes, with the forwarded-to user number No Yes No Yes Note -Notification of diversion to the calling user A may be provided as a network provider option. This service will be withdrawn by the service provider at the subscribers request
19、or for administrative reasons. 3.2 Normal procedures 3.2.1 Activatioddeactivatiodregistration Same as for Call Forwarding Unconditional (0 (see Recommendation 1.252.4). 3.2.2 Invocation and operation to B2, ., Bm, ., Bx. The final receiver of the call is C. The following illustration clarifies the C
20、FB procedures. Assume that A calls Bi, who forwards the call - - - B, 8, c A Bi T01024?4.92 3.2.2.1 Served user B,sperspectve If CFB is active and the served user is network determined user busy (NDUB) or user determined user busy (UDUB), then an incoming call to the served user will be forwarded. I
21、n case of NDUB, the call is not offered to the served user. 2 Recommendation 1.252.2 (08192) CCITT RECNNrI.252. 2 92 W 48b259L 0573870 138 In the case of UDUB, the call will have been offered to the served user. Normal call Set-up information will already have been provided to the served user. When
22、the forwarding attempt is started, the served user, as a subscription option, may receive notification that a call has been forwarded. No further notification is given. When an incoming call is forwarded without being offered to the served user (i.e. NDUB condition), the served user, as a subscripti
23、on option, may receive notification of the call forwarding (but will not be able to answer the incoming call). This notification is given as soon as the forwarding attempt is started. This notification includes the following information (on the call that has been forwarded): i) 2) 3) user-to-user in
24、formation; indication that a call has been forwarded; telecommunications service information (e.g., bearer capability, higher layer compatibility); 4) B,s number; and 5) calling party number A if the calling line identification presentation (CLIP) is applicable. If multiple forwardings have occurred
25、 and the served user is authorized to receive additional information he may also receive: 6) originally called number Bi; 7) cause for original forwarding; 8) last forwarding number B(,+i); 9) cause for last forwarding. 3.2.2.2 Forwarded-to user Cs perspective The forwarded-to user C will receive an
26、 indication that the call has been forwarded. As an option he may also receive: i) originally called number BI; 2) cause for original forwarding; 3) last forwarding number B,; 4) cause for last forwarding. (Depending on the use of other supplementary services, the forwarded-to user C may also receiv
27、e information such as the calling party A number and user-to-user signalling. See the description of interactions with other supplementary services.) 3.2.2.3 Calling user As perspective The following notification procedures for the calling user A are a network provider option. The notification proce
28、dures for calling user A shall only operate if the served user has subscribed to the option “calling user receives notification that call has been forwarded”. For the initial diversion and for any subsequent call forwarding no reply (CFNR), or call deflection (CD) after alerting has commenced, the n
29、etwork wili take the following actions depending on the subscription option parameter of the served user. 1) If this parameter is set to “calling user does not receive notifcation”, no notification is given to the calling user. 2) If this parameter is set to “notify calling user, without forwarded-t
30、o number”, then the calling user wili receive a notification that the call has been forwarded without the forwarded-to number, providing a previous diverting user has not requested that no notification is given as under item i) above. Recommendation 1.252.2 (08/92) 3 - - - - _ ._ - CCITT RECMN*I.252
31、m 2 92 48b2573 0573873 074 3) If this parameter is set to “notify caliing user, with forwarded-to number”, then the calling user will receive a notification that the call has been forwarded, providing a previous diverting user has not requested that no notification is given as under item 1) above. I
32、n addition, if alerting takes place (e.g. at user C), notification of the current forwarded-to number will be given when alerting commences if all served users in all previous diversions subscribe to “notify calling user, with forwarded-to number”. Transfer of the forwarded-to users number may be su
33、bject to number notification restrictions due to the invocation of other supplementary services at the forwarded-to user. 3.3 Exceptional procedures 3.3.1 Activation/deactivation/registration Same as CF (see Recommendation 1.252.4). 3.3.2 invocation and operation Call forwarding applies only to subs
34、cribed basic services. Calls to an ISDN number requesting a basic service which is not subscribed to, will never be forwarded. In cases where a user may be given the address of users involved in the call e.g. when the calling user may receive the forwarded-to users address, or when the forwarded-to
35、user may receive the forwarding users address and originally forwarding address (multiple forwarding), or when the served user may receive users addresses as part of that users notification and this address information is unavailable (e.g. due to address presentation restriction or interworking), th
36、e user who would have been given the address shall get an indication of the reason why no number can be given. Within an ISDN, or tandem ISDNs, the total number of all forwardings for each call should be limited. The maximum number of such connections should be limited to a value between tbree and f
37、ive for each call. This is to prevent infinite looping. If the limit is reached and an attempt is made to forward the call an additional time, then the forwarded call shall be treated as follows: If the forwarded call cannot be completed to the forwarded-to destination, then the network will clear t
38、he forwarded leg of the call. Specifically, if CFB has been invoked, and CFNR or CD after alerting has not occurred, then the call would be cleared back towards the calling user, and the calling user would be sent a cause to indicate that the call cannot be completed (Le. because of network congesti
39、on, invalid number, facility not available, etc.). This information shall not explicitly reveal that the call has been forwarded. Refer to Recommendations 1.252.3 or 1.252.5 respectively, for the case where the forwarded call cannot be completed and CFNR or CD, after alerting, has occurred. 3.4 Alte
40、rnative procedures 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 subscriber accurately for the service. 4 Recommendation
41、1.252.2 (08/92) CCITT RECMN*I.252. 2 72 W 4862573 0573872 TOO = 5 Interworking With diversion invoked across more than one network, e.g. from public switched telephone network (PSTN) via ISDN to another PSTN or between ISDNs of different countries, or even different continents, a decrease in Quality
42、 of Service parameters may arise. For example, the parameters that may be influenced are: - Call Establishment Time; - Transmission Delay; - BitErrorRatio; - Attenuation of Audio Signals. Depending on national implementations, the network may provide some precautions, e.g. limit the number of forwar
43、ding legs, limit the number of international border crossings, limit the number of satellite hops, etc. 5.1 Intenvorking with non-ISDN networks If the forwarded-to number is not within the ISDN, then an interworking situation is said to exist. The number of times a call will be forwarded once it has
44、 exited the ISDN network cannot be limited by 1 ISDN network. is If a forwarded call meets an interworking situation, then an interworking indication should be sent to the calling party, This indication shall not explicitly reveal that the call has been forwarded. In case of interworking, appropriat
45、e tones and/or announcements should be provided. Note - Once a call has been forwarded to a non-ISDN network, then further forwardings and/or notifications to the calling user are outside the scope of this Recommendation. 5.2 Intenvorkng with private ISDN This assumes cooperation between the public
46、and private networks. The forwarded-to number may be registered with the public network or the private ISDN. Further study is required to determine whether the latter should be a service provider option. If the private network detects forwarding back to a destination in the public network, the priva
47、te network could request that forwarding is performed by the public network. The private network may also specify either a transit network or a network specific facility or both to be used for that forwarding. Within ISDNs (public or private) the totai number of forwardings for each call should be l
48、imited (see Recommendation 1.252.4,s 3.3.2). If a private ISDN employs other types of service interactions than specified under 4 6, e.g. with completion of calls to busy subscribers (CCBS), the private ISDN shall supply the necessary precautions against such consequences. where a remote user is on
49、a different network, notifications to the remote user, if applicable, shall be sent to the remote users network for forwarding to the remote user. 6 Interaction with other supplementary services The ways in which Call Forwarding Busy interacts with other supplementary services are in general identical to the ways in which Call Forwarding Unconditional interacts with other supplementary services. Thus, if the interactions are described to be “same as CFU”, the CF text should be taken verbatim, except that the expression “Call Forwarding Unconditio
