1、CCITT RECMN*I.252. 4 92 = 4862593 0573895 508 INTERNATIONAL TELECOMMUN CATION UN ION CCITT TH E INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE 1.252.4 INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES (08/92) CALL FORWARDING UNCONDITIONAL Recommendat
2、ion 1.252.4 Geneva, 1992 FOREWORD The CCIIT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (RU). CCIT is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a
3、 view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCIIT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCIIT between Plenary Assemblies i
4、s covered by the procedure laid down in CCIIT Resolution No. 2 (Melbourne, 1988). Recommendation 1.252.4 was prepared by Study Group I and was approved under the Resolution No. 2 procedure on the 4th of August 1992. CCXT NOTES 1) telecommunication Administration and a recognized private operating ag
5、ency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a 2) A list of abbreviations used in this Recommendation can be found in Annex A O ITU 1992 Ali rights reserved. No part of this publication may be reproduced or utilized in any form or by any mean
6、s, electronic or mechanical, including photocopying and microfilm, without permission in writing from the IT. CCITT RECMN*I*252. 4 92 m 4862593 0573897 380 m Recommendation 1.252.4 CALL FORWARDING UNCONDITIONAL (revised 1992) 1 Definition Call forwarding unconditional permits a “served user” (see 8
7、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). The served users originating service is unaffected. If this service is activated, calls are forwarded no matter what the condition of the ter
8、mination. Other call forwarding services provide for call forwarding based on condition, e.g. Call Forwarding Busy and Call Forwarding No Reply. The forwarded-to number is registered with the network for use on all calls. Note - In normal situations, the Call Forwarding Unconditional service is prov
9、ided 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 a single interface; in addition, it may not understand a complete ISDN number (e.g. Direct-Dialling-In), In these cases, the Ca
10、ll Forwarding Unconditional 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 number, Call Forwarding Unconditional (CFU) service (including options) may be subscribed to for each basic service to wh
11、ich the user(s) of the number subscribes, or collectively for ali the basic services to which the user(s) subscribes. Since subscription is on an ISDN number basis, the same call forwarding subscriptions will apply to all terminals using this number. Note - In this service description, it is assumed
12、 that a single ISDN number is not shared across multiple interfaces. A single ISDN number may, however, be shared by multiple terminals on the same interface. Procedures permitting an ISDN number to be shared across multiple interfaces are for further study. For multiple access installations, it may
13、 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 different forwarded-to number for each basic service subscription parameter value to which he has subscribed. An ind
14、ication that the CFU 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 special indication in the proceed response. 2.2 Specific terminology Served user: User of a particular ISDN numb
15、er 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 forwarded. 2.3 Qualflcations on the applicability to telecommunication services No restrictions identified. Recom
16、mendation 1352.4 (OW92) 1 3 Procedures 3.1 Provisodwithdrawal CFV shall be provided after pre-arrangement with the service provider. 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 opti
17、on, only one value can be selected. Subscription options are summarized below: Subscription options Value Served user receives notification No that the call has been forwarded Yes, with infomation about the call (see 0 3.2.2) Calling user receives notification No that the cal has been forwarded Yes,
18、 without the forwarded-to user (see Note) number Yes, with the forwarded-to user UUber Served user receives notification No that CFU is currently activated Yes Served user releases hisher No number to forwarded-to user Yes Note -Notification of diversion to the calling user A may be provided as a ne
19、twork provider option. This service will be withdrawn by the service provider at the subscribers request or for administrative I reasons. 3.2 Normal procedures 3.2.1 Actvatoddeactvatiodregstration If the served user has subscribed to Cnr, the served user will use the activation procedure. To activat
20、e CFU, the served user must supply: 1) the forwarded-to address: 2) information as to whether all calls or al calls of a specified basic service should be forwarded; 3) possibly the ISDN number for which CFU should apply. As a network option, verification of the forwarded-to number should be accompl
21、ished, if possible, before accepting the cal forwarding request. 2 Recommendation 1.252.4 (OW92) CCITT RECMN*Im252m 4 92 m 4862593 0573899 353 m When the served user so activates CFV, the service provider will return notification of acceptance or rejection of the request (see Exceptional procedures,
22、 0 3.3, for a list of possible causes for rejection). This notification will include the number of forwarded-to users to whom the call forwarding is active. If a single number can be used by more than one terminal, activation of CFV will be possible from any terminal which uses this number. 011 succ
23、essful activatioddeactivation, the activatioddeactivation response from the network wiil be sent to ail terminals. If the activatioddeactivation is unsuccessful, then the network shall inform only the terminal which requested the activatioddeactivation. As a service option, activatioddeactivation ma
24、y be restricted to selected terminals (users) (e.g. by use of a password). CFU can be deactivated in either of two ways. The user can specificaliy deactivate the CFU activation. The user can activate CFU for the specified basic service to another number, thus causing the previous invocation of CFU t
25、o be overridden. 3.2.2 Invocation and operation The following illustration clarifies the CFU procedures. Assume that A calls BI, who forwars the cali to B2, ., Bm, ., B,. The final receiver of the cai1 is C. 3.2.2.1 Served user Bms perspective When CFU is active, all incoming calis wili be forwarded
26、 without being offered to the served user B,. When an incoming call is forwarded without being offered to the served user, the served user, as a subscription option, may receive notification of the cali forwarding (but will not be able to answer the incoming cali). This notification is given as soon
27、 as the forwarding attempt is started. This notification includes the following information (on the cali that has been forwarded): 1) 2) 3) user-to-user information; 4) B,s number; indication that a cali has been forwarded; telecommunications service information (e.g. bearer capability, higher layer
28、 compatibility); 5) caiiing party number A if Caiiing Line Identification Presentation (CLIP) is applicable. If multiple forwardings have occurred and the served user is authorized to receive additional information, he 6) originally called number B 1; may also receive: 7) cause for original forwardi
29、ng; 8) last forwarding number B(m-); 9) cause for last forwarding. Recommendation 1.252.4 (08/92) 3 3.2.2.2 Forwarded-to user C?s perspective The forwarded-to user C will receive an indication that the call has been forwat ?rd. As an option he may also receive: 1) originally called number BI; 2) cau
30、se for original forwarding; 3) last forwarding number Bx; 4) cause for last forwarding. (Depending on the use of other Supplementary services, the forwarded-to user C may also receive information such as the calling party A number and user-to-user signalling, See the description of interactions with
31、 other supplementary services.) 3.2.2.3 Calling user A?s perspective The foilowing notification procedures for the calling user A are a network provider option. The notification procedures for cailing user A shall only operate if the served user has subscribed to the option ?calling user receives no
32、tification that cail 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 network will take the following actions depending on the subscription option parameter of he served user. If this param
33、eter is set to ?calling user does not receive notification?, no notification is given to the calling user. If this parameter is set to ?notify calling user, without forwarded-to number?, then the calling user will receive a notification that the call has been forwarded without the forwarded-to numbe
34、r providing a previous diverting user has not requested that no notification is given as under 1) above. If this parameter is set to ?notify calling user, with forwarded-to number?, then the calling user will receive a notification that the call has been forwarded providing a previous diverting user
35、 has not requested that no notification is given as under 1) above. In 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 forw
36、arded-to number?. 1) 2) 3) Transfer of the forwarded-to user?s number may be subject to number notification resirictions due to invocation of other supplementary services at the forwarded-to user. 3.3 Exceptional procedures 3.3.1 Activatioddeactivatiodregistration 3.3.1.1 Activation Call Forwarding
37、Unconditional for all basic services and Call Forwarding of particular basic services cannot be activated simultaneously. If the system cannot accept an activation request, the served user should receive a notification that call forwarding activation was unsuccessful. Possible causes are: i) service
38、 not subscribed; ii) forwarded-to ISDN number invalid; iii) use of an operator access prefix; iv) forwarded-to ISDN number?s telecommunication services violate subscribed constraints (e.g. group restrictions); Recommendation 1.252.4 (08/92) CCITT RECMN*I.252. 4 92 48b2591 0573901 631 = v) forwarded-
39、to ISDN number is a free number within the same office (Le. a number to which no call is chargeable): vi) insufficient information: vii) requested telecommunication service is not provided to the forwarded-to ISDN number: viii) forwarded-to number is a special service code (e.g. police); ix) forward
40、ed-to number is served users number. However, the network is not required to validate information related to the forwarded-to user. 3.3.1.2 Deactivation If the user does not specify completely which CFU request is to be deactivated (e.g. the basic service and/or the originators number), the network
41、will reject the deactivation request with appropriate cause. If the network cannot accept a users request for deactivation, the cause will be returned to the user, e.g. incorrect origination ISDN number used. If the network deactivates CFU without the served user having requested deactivation (e.g.
42、when an exceptional condition occurs), the served user will receive notification along with the cause. 3.3.2 Invocation and operation Call forwarding applies only to subscribed basic services. Calls to an ISDN number requestigg a basic service which is not subscribed to, will never be forwarded. In
43、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 user may receive the forwarding users address and originally forwarding address (multiple forwarding), or when the served user may
44、 receive users addresses as part of that users notification and this address information is unavailable (e.g. due to address presentation restriction or interworking), the user who would have been given the address shall get an indication on the reason why no number can be given. Within an ISDN, or
45、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 three and five for each call. This is to prevent infinite looping. If the limit is reached and an attempt is made to forward the call an addi
46、tional time, then the forwarded call shali be treated as follows: If the forwarded call cannot be completed to the forwarded-to destination, then the network will clear the forwarded leg of the call. Specifically, if CFU has been invoked, then the call would be cleared back towards the calling user.
47、 If the call has not previously undergone CFNR or CD after alerting, the call will be cleared all the way back to the calling user and the calling user will be informed that no user is responding. This information shall not explicitly reveal that the call has been forwarded. Refer to Recommendations
48、 1.252.3 or 1.252.5 respectively, for the cases where the forwarded call cannot be completed and CFNR or CD after alerting has occurred. 3.4 Alternative procedures None identified. 4 Network capabilities for charging This Recommendation does not cover charging principles. Future Recommendations in t
49、he D-Series are expected to contain that information. It shall be possible to charge the subscriber accurately for the service. Recommendation 1.252.4 (OW92) 5 - - . _-_ - CCITT RECMN*I.252. 4 92 W 4462591 O573902 578 W 5 Interworking requirements 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 of Service parameters may arise. For example, the parameters that may be influenced
