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FOREWORD The CCITT (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 tar- iff questions and issuing Recommendations on them with a view to standard- izing 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 by the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988). Recommendation I.253.1 was prepared by Study Group I and was approved under the Resolution No. 2 procedure on the 2July1990. ___________________ CCITT NOTE In this Recommendation, the expression "Administration" is used for shortness to indicate both a telecommunication Administration and a recog- nized private operating agency. πITU1990 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopy- ing and microfilm, without permission in writing from the ITU. PAGE BLANCHE Recommendation I.253.1 CALL WAITING (CW) SUPPLEMENTARY SERVICE1) 1 Definition The Call Waiting service is a supplementary service which permits a sub- scriber to be notified of an incoming call (as per basic call procedures) with an indication that no interface information channel is available. The user then has the choice of accepting, rejecting or ignoring the waiting call (as per basic call procedures). 2 Description 2.1 General description The ISDN Call Waiting service allows an out-of-band notification to sub- scriber B of the incoming call; this is the assumed case for this definition (for optional in-band indications, see AnnexA). The maximum number of calls that can be handled (e.g. active, held, alert- ing, waiting) for each ISDN number on a given interface is specified at sub- scription time. Note - The situation where at least one B-channel is available may be, for a given terminal, a situation similar to the one where all B-channels are busy. A terminal receiving a call request and already having an active call, may process the new incoming call in the same way as it would have processed a call if no B-channel were available, i.e. react positively to the incoming call request. Moreover, when at least one B-channel is free, any compatible busy terminal of subscriberB can react positively to an incoming call. 2.2 Specific terminology Throughout this Recommendation the following terminology will be used: Subscriber B: the subscriber who is provided by the network with the Call Waiting service on a particular interface. User B: the user who reacts to the call waiting at B. User C: the user who has originated a call to B which causes the Call Waiting service to be invoked. User A: represents a user who is engaged in a call with user B (this call can be in any state). User Response timer T1: this timer specifies the period the network will wait for a positive response, from a terminal atB, to the offered call. It is part of the basic call and has a value of a few seconds. No Answer timer T2: this optional timer specifies the period the net- work will wait for a response (answer), from userB, to the offered call from userC. The value of this timer is between0.5 and2minutes. 2.3 Qualifications on the applicability to telecommunication ser- vices This supplementary service is considered meaningful when applied to the Telephony teleservice and the speech and 3.1kHz audio bearer ser- vices. Furthermore, it may also be meaningful when applied to other ser- vices. 3 Procedures 3.1 Provision/withdrawal Call Waiting (CW) can be provided on a subscription basis or, as a network provider option, be generally available to all users without subscrip- tion. Call Waiting can be withdrawn for administrative reasons. As part of each applicable bearer service or teleservice, there is an option specifying the maximum number of information channels which can be used (occupied) on the interface for each ISDN number, all ISDN num- bers or subsets of ISDN numbers. Call Waiting for bearer services or teleser- vices occurs when an attempt is made to exceed these limits. As a network provider option, Call Waiting can be offered with sev- eral subscription options. The options apply separately to each ISDN number and service combination. For each subscription, only one value can be selected. Subscription options are summarized below: include 253-1T1E Subscription optionsValue Calls that can wait Calling user receives notification call is waiting _ All _ Others are for further study _ No _ Yes In addition, the following subscription options can be specified for each ISDN number, all ISDN numbers, or subsets of ISDN numbers on each interface: include 253-1T2E Subscription optionsValue Maximum number of calls which can be waiting _ One _ l, where 1 · l · n _ m Note _ The parameters m (maximum number of information channel) and n (maximum number of total calls present) are defined in the relevant basic service description (refer to RecommendationI.231 andI.241. The use of T2 is a service provider option. When used, the value of T2 shall be set by the service provider as a default value subject to change only by the service provider. 3.2 Normal procedures 3.2.1 Activation/deactivation The CW supplementary service is activated by the service provider at provi- sion. The CW supplementary service is deactivated by the service pro- vider at withdrawal. Registration does not apply Note - The introduction, as a network option, of the possibility for a user to activate and deactivate the CW supplementary service in the network may be a long-term enhancement. 3.2.2 Invocation 3.2.2.1 When an incoming call from user C arrives at the access of sub- scriber B and encounters the channels busy condition, and a network deter- mined user busy (NDUB) condition does not result, then the Call Waiting service will be invoked and the call shall be offered to subscriberB with an indication that the channels busy condition exists. 3.2.3 Operation 3.2.3.1 If a response is received from a terminal at the B access, within the normal basic call period, that the user(s) is (are) being informed about the incoming call, then userC will be given an indication that the called user(s) is (are) being informed of the incoming call. In some networks this indication may also indicate that call waiting is in operation. 3.2.3.2 If either user A or user B requests that the active call is terminated, then this call shall be terminated as for a basic call. UserB shall then be able to accept the waiting call from user C using normal information channel selection procedures before the expiry of T2. 3.2.3.3 User B can also free resources by using the Call Hold supplementary service. User B shall then be able to accept the waiting call from user C using normal information channel selection procedures before the expiry of T2. 3.2.4 Subscriber resources in use When an incoming call from user C arrives at the access of sub- scriber B and there is a B-channel available, the call shall be indicated to subscriber B. If a terminal at the access of subscriber B is busy because of another call but is able to accept the incoming call from user C, it may indi- cate to the network that the called user is being informed about the incoming call. 3.3 Exceptional procedures 3.3.1 Activation/deactivation/registration Non identified. 3.3.2 Invocation Non identified. 3.3.3 Operation 3.3.3.1 Incoming call from user C ignored by subscriber B If the optional No Answer timer T2 expires without any acceptance from subscriber B of the incoming call, then the network shall inform subscriberB that the call is no longer waiting and also inform userC that his call cannot be connected. Normal release applies to the call attempt from userC (the call is cleared indicating no response) with an appropriate indica- tion given to userC. 3.3.3.2 Incoming call from user C rejected by user B A rejection of the waiting call by one of the terminals on the inter- face of subscriber B will not stop the optional No Answer timerT2 as another terminal may subsequently accept the waiting call within the remainder of the specified period. Such a rejection may, however, cancel any indication provided to that terminal. Where rejections of a waiting call have been received from all those terminals that responded with an alerting indi- cation before the expiry of the optional No Answer timerT2, then the net- work shall inform userC that his call cannot be connected. Normal release applies to the call attempt from userC with the call being cleared indicating user rejection. SubscriberB is notified that the call is no longer waiting. 3.3.3.3 Release by user C within the specified period If calling user C informs the network, before the expiry of the optional No Answer timerT2, that he wishes to release his call attempt to subscriberB, then the network shall inform subscriberB of this situation and initiate release of the call attempt from userC. 3.3.3.4 No positive response terminals at subscriber B's interface If no positive response that user(s) are being informed of the waiting call is received from a terminal at subscriberB's interface during the normal call period (User Response timerT1), then the call attempt from userC shall be released by the network with userC being given the reason for the release. 3.3.3.5 No reasons available If user B accepts a call and network resources do not exist to com- plete the call (i.e. no information channels are available), the network will indicate an error to userB with cause _no B-channels available_. The net- work will not clear the call but will wait for another userB indication for acceptance, until userC clears the call or the optional No Answer timerT2 expires. 3.3.3.6 Maximum number of waiting calls reached Subscriber B shall be considered as busy when the limit on the max- imum number of calls which can be waiting has been reached. Any incoming call during this period shall be handled accordingly. 3.4 Alternative procedures 3.4.1 Activation/deactivation/registration 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 subscriber accurately for the ser- vice. 5 Interworking requirements Calls originating from outside the ISDN can undergo call waiting at the access of subscriber B with no impact on subscriber B's service (see AnnexA). As a service provider option, a special in-band indication may be provided to the calling user instead of the normal alerting indication. 5.1 Interworking with private ISDNs When user C is on a different network from subscriber B (e.g. one user on a private ISDN and the other user on a public ISDN), then indica- tions to userC, if applicable, shall be sent to the network to which userC is attached for forwarding to userC. 6 Interaction with other supplementary services 6.1 Call Waiting Not relevant. 6.2 Call Transfer User B, who has subscribed to both Call Waiting and Call Transfer services, cannot transfer a waiting call from userC until he first establishes a connection to userC. Assume that user B is on an active call with user A and has received an indication of a waiting call from userC. UsersA andB have Call Waiting subscribed for their accesses and userB has subscribed to the Call Transfer service. UserB intends to transfer userA to userD. _ User B may receive an indication of a waiting call from user C either before or during the transfer of userA to another party. The call waiting indication may be presented regardless of the type of transfer invoked by userB (i.e.for Normal, Single Step, or Explicit transfers). When userA has been transferred, a B-channel would normally become idle, enabling the waiting call to be answered by userB. _ If user A has a call waiting indication before or during the transfer process, then upon successful completion of the transfer of userA to userD, userA shall retain the waiting call indication. UserA could use normal call waiting procedures (if desired) to accept the waiting call. _ If user D receives a call waiting indication during the transfer pro- cess, e.g. while being in a call with userB, then upon successful comple- tion of the transfer of userA to userD, userD shall retain the waiting call indication. UserD could use normal call waiting procedures (if desired) to accept the waiting call. In general, a call waiting indication may be delivered to users A or B (and to user D during the transfer process) when the called user has sub- scribed to the Call Waiting service. 6.3 Connected Line Identification Presentation (COLP) No impact, i.e. neither supplementary service affects the operation of the other supplementary service. When user B uses one of the call waiting procedures to accept a waiting call (within any time limits established by the service provider), userC will be informed of the connection. The confirmation that a connec- tion has been established may provide the connected user B'snumber. 6.4 Connected Line Identification Restriction (COLR) No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.5 Calling Line Identification Presentation (CLIP) No impact, i.e. neither supplementary service affects the operation of the other supplementary service. If the user(s) at B is(are) given a call waiting indication, and has (have) subscribed to the CLIP service, then the calling user number shall be presented to the users atB at the time the call waiting indication is given. 6.6 Calling Line Identification Restriction (CLIR) No impact, i.e. neither supplementary service affects the operation of the other supplementary service. Assume a user at C, who has subscribed to the CLIR service, reaches a user(s) at B, who has subscribed to the Call Waiting service. On invocation, the user atB would receive a call waiting indication but would not receive userC's number when the call waiting indication is given. 6.7 Closed User Group No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.8 Conference Calling A user at B who is active on any type of conference call may receive an indication of a waiting call. Once a conference has been established: i) Any party that has activated Call Waiting will be able to receive an indication of an incoming call, and could place his connection to the conference on hold to accept the waiting call. ii) The Conference Controller could, if desired, add the party from the waiting call, by answering the waiting call and using the _add party from existing call_ procedures. 6.9 Direct-Dialling-In No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.10 Call Diversion (Call Forwarding) services 6.10.1 Call Forwarding Busy No impact, i.e. neither supplementary service affects the operation of the other supplementary service. Note _ The following text clarifies the situation. If user B is NDUB (Network Determined User Busy), call forwarding busy shall take place, and the call is not offered. If userB is not NDUB, the call shall be offered, and if the UDUB (User Determined User Busy) condition results, then call for- warding busy shall take place. 6.10.2 Call forwarding no reply If subscriber B has call forwarding no reply (CFNR) activated, then a waiting call shall be offered as described in this definition. If no answer is received to this call within the duration of the CFNR timer, then the CFNR service is invoked and the call is forwarded as per that service definition. 6.10.3 Call Forwarding Unconditional If subscriber B has activated Call Forwarding Unconditional, then the execution of that forwarding condition takes precedence over Call Wait- ing. Call Forwarding Unconditional can be activated while a call is waiting without changing the state of the waiting call. 6.11 Line Hunting The Call Waiting service should not be provided to a line in a hunt group. 6.12 Three-Party Service A user at B who is involved in a Three-Party Service operation (with minimal Three-Party Service or active in a three-way conversation) may receive an indication of a waiting call. The procedures and restrictions for handling the waiting call are defined in the Three-Party Service description. 6.13 User-to-User Signalling User-to-user information (UUI) (service 1) included in the call set- up message will be delivered to subscriberB with the Call Waiting indica- tion. UUI (service 2) sent from the calling user to the called user during the alerting phase is allowed to be sent when a point-to-point configuration exists at the called side. If the called user subscribes to User-to-User Signalling, he may include UUI (service 1) in a rejection of a waiting call when a point-to-point configuration exists at the called side. There is no interaction with user-to-user service 3. 6.14 Multiple Subscriber Number No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.15 Call Hold When an ISDN user receives a call waiting indication the ISDN user may use the Call Hold service to hold his active call and answer the waiting call. Use of the hold service does not place a call into a waiting state. 6.16 Advice of Charge No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.17 Multi-Level Precedence and Preemption (MLPP) service a) The incoming call is of the lowest precedence level (precedence level4): 1) One or more MLPP calls are of the lowest precedence level: no interaction; Call Waiting service is invoked. 2) All MLPP calls are precedence calls: Call Waiting service is invoked. If in-band call waiting tone is being applied as a network provider option, then the tone should not be provided in this case since it would disrupt a higher pre- cedence call. b) The incoming call is a precedence call: 1) One or more MLPP calls are of lower precedence than the incoming call: An MLPP call of the lowest precedence level is preempted unless the called subscriber is non-preemptable. If the called subscriber is non-preemptable, Call Waiting service is invoked and the precedence level of the incoming call is provided to the called user along with call waiting indication. 2) One or more MLPP calls are of the same precedence and the rest of the MLPP calls are of higher precedence than the incoming call: Call Waiting service is invoked. The precedence level of the incoming call is provided, along with call waiting indication, to the called users on MLPP calls at the same precedence level as the incoming call. If the called user is on an MLPP call at a higher precedence level, call waiting service is invoked. If the in-band call waiting tone is being applied as a network provider option, then the tone should not be provided in this case since it would disrupt a higher precedence call. 3) All the MLPP calls are of higher precedence: Call Waiting service is invoked. If in-band call waiting tone is being applied as a network provider option, then the tone should not be provided in this case since it would disrupt a higher pre- cedence call. 6.18 Priority service No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 7 Dynamic description The dynamic description of this service is given in Figure 1/I.253.1. FIGURE 1/I.253.1 (Sheet 1 of 5) FIGURE 1/I.253.1 (Sheet 2 of 5) FIGURE 1/I.253.1 (Sheet 3 of 5) FIGURE 1/I.253.1 (Sheet 4 of 5) FIGURE 1/I.253.1 (Sheet 5 of 5) ANNEX A (to Recommendation I.253.1) Optional in-band indications A.1 In-band call waiting indication In addition, as a service provider option, audible in-band indications may be provided to the channels occupied with the speech bearer service and the telephony teleservice. Where applied, tones should be in accordance with RecommendationE.180. A.2 Activation/deactivation In addition, under the in-band call waiting indication option, sub- scriber B may activate and deactivate call waiting in-band indications with an appropriate request. Whether, and if so, to what degree, activation/deacti- vation is supported by the network may be network dependent. If supported, then the network shall inform subscriber B (all terminals on the access) of the success, or other outcome, of this action. A.3 Interworking requirements If an ISDN subscriber B receives a call from a non-ISDN calling user, the network will send the call waiting indication to subscriberB in the normal way. In addition, under the in-band call waiting indication option, an in-band indication will be applied to channels occupied with the 3.1kHz audio bearer service (where the call originated from the PSTN as identified by a progress indicator), only if it is destined to a number designated for in- band notification by the call waiting subscriber. ANNEX B (to Recommendation I.253.1) Additional _Busy_ information B.1 The following subscription option and definition text (ref. CCITT ReportCOMXVIII-R15) is included in this definition pending publication in RecommendationI.221. The following subscription option is applicable to the interface as a whole regardless of service: include 253-1T3E Subscription optionsValue Maximum number of information channels on the interfacec B.2 Resource busy conditions a) Channels busy _ This condition occurs when there is no appropriate information channel (physical or logical) available for the network to use for the call. It may be due to exceeding the information chan- nel limit associated with the service or with the interface. b) Maximum number of total calls reached _ This condition occurs when the maximum number of total calls supported either at the given subscriber's interface(s) or for a given service has been reached.