1、- CCITT RECflN*I.252. 3 92 4862573 0573883 896 m INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES 1.252.3 (08/92) CALL FORWARDING NO REPLY Recommendation
2、1.252.3 Geneva, 1992 CCITT RECMN*I*252- 3 92 4862593 0573884 722 INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES 1.252.3 (08/92) CALL FORWARDING NO REPLY
3、 Recommendation 1.252.3 Geneva, 1992 - - - - -_ CCITT RECMN*I-252- 3 92 m 4862591 0573885 669 FOREWORD The CCI” (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union OTU). CCIT is responsible for studying technical, opera
4、ting and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCIT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of R
5、ecommendations by the members of CCm between Plenary Assemblies is covered by the procedure laid down in CCIIT Resolution No. 2 (Melbourne, 1988). Recommendation 1.252.3 was revised by Study Group I and was approved under the Resolution No. 2 procedure on the 4th of August 1992. CCIil NOTES 1) telec
6、ommunication Administration and a recognized private operating agency. 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 IT 1992 All rights reserved. No part of this pub
7、lication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfiim, without permission in writing from the IT. CCITT RECMN*I.252- 3 92 m 4862593 0573886 5T5 m Recommendation 1.252.3 CALL FORWARDING NO REPLY (revised 1992) 1 Definition C
8、all Forwarding No Reply permits a “served usei (see 4 2.2) to have the network send to another number all incoming calls for the served users ISDN number which meet no reply, or just those associated with a specified basic service which meet no reply. The served users originating service is unaffect
9、ed. The forwarded-to number is registered with the network for use on all calls. Note - In normal situations, the Call Forwarding No Reply 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 rec
10、ognize 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 Call Forwarding No Reply service is offered on the basis of the part of the ISDN number which the network can recognize. 2 Description 2.1 General
11、description For a given ISDN number, the Call Forwarding No Reply (CFNR) service (including options), may be subscribed to for each basic service to which 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 ISD
12、N number basis, the same call forwarding subscriptions will apply to all terminals using this number. Two conditions of CFNR are possible as follows: 1) 2) Only case 2) is considered here. Case 1) is for further study. Note - In this service description, it is assumed that a single ISDN number is no
13、t 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 be possible for the user to spe
14、cie, on activation, if the service is applicable to a specific access or all accesses associated with that installation. the call is offered and no indication of a compatible terminal is received; or the cal is offered and an indication of a compatible terminal is received. The served user can reque
15、st a different forwarded-to number for each basic service subscription parameter value to which he has subscribed. An indication that the CFNR 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
16、form of a special indication in the proceed response. 2.2 SpecBc terminology Served user: User of a particular ISDN number who is requesting that calls to his number be forwarded. This Fonvarded-to-user: User to whom the call shall be forwarded. user may also be referred to as the forwarding user or
17、 the called user. 2.3 Qualcations on the applicability to telecommunications services No restrictions identified. Recommendation 1.252.3 (08/92) 1 3 Procedures 3.1 Provisiodwithdrawal CFNR shall be provided after pre-arrangement with the service provider. The service can be offered with five subscri
18、ption options. Options apply separately to each basic sen .ce 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 notification that the call has been forwarded Calling us
19、er receives notification that the caU has been forwarded (see Note) No reply condition timer Served user receives notification that CFNR is currently activated Served user releases hisher number to forward-to user Value No Yes (see 0 3.2.2) No Yes, without the forwarded-to user number Yes, with the
20、forwarded-to user number 5-60 seconds, in steps of 5 seconds 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 or for administrative reasons. 3.2 Normal p
21、rocedures 3.2.1 Activatioddeactivatiodregistration Same as for Call Forwarding Unconditional (CFU) (see Recommendation 1.252.4). 3.2.2 Invocation and operation The following illustration clanfies the CFWR procedures. Assume that A calls Bi, who forwards the call to B2, , Bm, ., B,. The final receive
22、r of the call is C. -/-y - -0 s, sx c A SI T0102430.92 2 Recommendation 1.2523 (08/92) CCITT RECMN*I-252. 3 72 W 4862571 0573888 378 W When forwarding occurs, the network may either: a) retain the call at the served user until alerting commences at the forwarded-to user (that alerting causing the ca
23、ll to be removed from the served users access); or clear the cail to the served user on acceptance of the call forwarding request. b) 3.2.2.1 Served user Bms perspective When CFNR is active, incoming calls will be offered to the served user. Normal call offering information is provided to the served
24、 user, If the served user does not reply within a subscribed time interval, the call wiil be forwarded. The served user, as a subscription option, may receive notification that a cal has been forwarded. This notification is given as soon as the forwarding attempt is stated. No further notification i
25、s given. 3.2.2.2 Fonvarded-to user Cs perspective The fonvarded-to user C will receive an indication that the call has been forwarded. As an option he may also receive: 1) originally called number BI; 2) cause for original forwarding; 3) last forwarding number B,; 4) cause for last forwarding. (Depe
26、nding 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 other supplementary services.) 3.2.2.3 Calling user As perspective The following notificatio
27、n procedures for the calling user A are a network provider option. The notification procedures for calling user A shall only operate if the served user has subscribed to the option “calling user receives a notification that cail has been forwarded”. For the initial diversion and for any subsequent C
28、FNR or call deflection (CD) after alerting has commenced, If this parameter 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 fonvarded-to number”, then the calling user will receive a notif
29、ication 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 1) above. 3) If this parameter is set to “notify calling user, with forwarded-to number”, then the calling user will receive a n
30、otification that the call has been forwarded, providing a previous diverting user has not requested that no notification is given as under item 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 se
31、rved users in all previous diversions subscribe to “notify calling user, with forwarded-to number”. the network wiil take the following actions depending on the subscription option parameter of the served user. i) 2) Transfer of the forwarded-to users number may be subject to number notification res
32、trictions due to the invocation of other supplementary services at the forwarded-to user. 3.3 Exceptional procedures 3.3.1 Activatioddeactivationregistration Same as CFU (see Recommendation 1.252.4). Recommendation 1.252.3 (08/92) 3 -_ _I_- - - - - _ CCITT RECMN*1.252- 3 92 m 4862591 0573889 204 m 3
33、.3.2 Invocation and operation Cali forwarding applies only to subscribed 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
34、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 receive users addresses as part of that users notification and this address information is unavailable (
35、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 tandem ISDNs, the total number of all forwardings for each call should be limited. The maximum number of
36、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 additional time, then the forwarded call shall be treated as follows: If the forwarded call cannot be complet
37、ed to the forwarded-to destination, then as a service provider option a) Clear the forwarded leg of the call and continue to alert the served user. The calling user will, in the case of a telephony call, continue to receive in-band ringing tone. The “no reply” timer need not be restarted. However, a
38、s a network option, the “no reply” timer may be restarted at this point. (Note that, with this option, during the invocation of CFNR the forwarding user shall continue to be alerted until alerting commences at the forwarded-to user). Clear the call back towards the calling user and the calling user
39、would be sent a cause to indicate that the cali cannot be completed (i.e. because of network congestion, invalid number, facility not available, etc.). This information shall not explicitly reveal that the call has been forwarded. If CFNR or CD, after alerting, has previously occurred, then the cali
40、 would be cleared back towards that served user; refer to Recommendations 1252.3 or 1252.5 respectively, for these cases. (Note that, with this option, the alerting of the forwarding user shall have ceased on invocation of CFNR.) the network may either: b) 3.4 Alternative procedures None identified.
41、 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. 5 Interworking requirements With diversion invoked a
42、cross 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 are: - Call Establ
43、ishment Time; - Transmission Delay; - Bit Error Ratio; - Attenuation of Audio Signals. 4 Recommendation 1.252.3 (08/92) I CCITT RECflN*I.252- 3 92 = 48bZ593 0573890 T2b I Refer to Recommendation 1.253.1, Q 6.10, Interaction with CFNR. Depending on national implementations, the network may provide so
44、me precautions, e.g. limit the number of forwarding legs, limit the number of international border crossings, limit the number of satellite hops, etc. 5.1 Intenvorking with non-ISDN nehvorks If the forwarded-to number is not within the ISDN, then an interworking situation is said to exist. The numbe
45、r of times a call will be forwarded once it has exited the ISDN network cannot be limited by this ISDN network. If a forwarded call meets an interworking situation, then an interworkhg indication should be sent to the caling party. This indication shall not explicitly reveal that the call has been f
46、orwarded. In case of interworking, appropriate 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 Intenvorking with private ISD
47、N This assumes cooperation between the public 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. I the private network detects forwarding back to a
48、 destination in the public network, the private network could request that forwarding is performed by the public network. The private network may also optionally specify either a transit network or a network specifk facility or both to be used for that forwarding. Within ISDNs (public or private) th
49、e total number of forwardings for each call should be limited (see Recommendation 1.252.4, 0 3.3.2). If a private ISDN employs the other types of service interactions than specified under 0 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 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 se
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