22.0833GPPCall Waiting (CW) and Call Holding (HOLD)Stage 1Supplementary ServicesTS
The Call Waiting Service permits a mobile subscriber to be notified of an incoming call (as per basic call procedures) whilst the traffic channel is not available for the incoming call and the mobile subscriber is engaged in an active or held call. Subsequently, the subscriber can either accept, reject, or ignore the incoming call.
This service operates when the traffic channel at the controlling subscriber B is not available and B is engaged in an active or held call.
When a third party (calling subscriber C) attempts to connect to that termination, the controlling subscriber B is given an appropriate indication of the waiting call. A notification that the call is waiting will be sent back towards the calling subscriber C.
The maximum number of waiting calls at one time per mobile access is one. This means that no further calls are offered to the subscriber while a call is waiting.
NOTE: As a network option this maximum number of waiting calls may be greater than one. This is considered as a possible future enhancement.
1.2.2 Applicability to telecommunication services
The applicability of this Supplementary Service to the ongoing call is defined in TS 22.004 . The incoming, waiting, call may be of any kind.
(Controlling) subscriber B
This is the subscriber who is provided by the network with the Call Waiting Service and who reacts to the Call Waiting.
This is the subscriber who has originated a call to B which causes the Call Waiting Service to be invoked.
This represents a subscriber who is engaged in a call with B, being either the calling or the called party.
T2; No answer time out
The duration of this time out is the time the network will wait for a response from subscriber B, to the offered call from subscriber C. The value of the timer is between 0.5 and 2 minutes at the service providers discretion.
1.3 Normal procedures with successful outcome
This Supplementary Service is provisioned for all Basic Services (BS) subscribed to and to which it is applicable, i.e. not provisioned to any subset of these BS.
Withdrawal will be at the request of the subscriber or for administrative reasons.
This Supplementary Service will be activated either collectively for all applicable Basic Services or on a Basic Service group basis by the subscriber using a control procedure, as specified in TS 22.030 , or by the service provider. The controlling subscriber shall be informed by the network of the success or otherwise of her action.
The service will be deactivated either collectively for all applicable Basic Services or on a Basic Service group basis by the subscriber using a control procedure, as specified in TS 22.030 , or by the service provider. The controlling subscriber shall be informed by the network of the success or otherwise of her action.
This service is invoked by the network on arrival of an incoming call if the service is active and the controlling subscriber B’s traffic channel is not available, B is engaged in an active or held call and there is no other call currently waiting.
1.3.8 Normal operation with successful outcome
220.127.116.11 Incoming call from C
When an incoming call from subscriber C arrives, the served mobile subscriber is connected to – at least – one call (active or held) and a NDUB (Network Determined User Busy) condition does not exist, then the CW service shall be invoked and the call shall be offered to subscriber B with an appropriate indication, e.g. with a "Call Waiting Tone".
If a response to the offered call is received from the mobile termination at B, then the subscriber C shall be given an indication (e.g. ringing tone) that the called subscriber is being informed of the incoming call and, if possible, that call waiting is in operation.
18.104.22.168 Terminating call by A or B
If either subscriber A or subscriber B requests that the call is terminated, then this call shall be terminated as for basic call (see TS 22.030  for more information). Subscriber B shall then be given the normal notification that there is a new call to her, as for a normal terminating call. The network shall continue to indicate; e.g. ringing tone towards subscriber C as for a normal call. B can then accept the call from C before the expiry of T2.
Subscriber B can also free resources by using the Call Hold Supplementary Service. Subscriber B shall then be able to accept the waiting call from subscriber C before the expiry of T2.
Alternatively, subscriber B may specifically request release or hold of the connection to A and accept the waiting call as one action (see TS 22.030 ). In this case, the network connects subscriber B to subscriber C with no further notifications to either subscriber. This must be done before the expiry of T2.
The controlling subscriber may interrogate the network by the use of a control procedure, as specified in TS 22.030 . The network shall respond with an appropriate indication telling the subscriber whether the service is supported in this network and, if so, provide a list of all Basic Service groups to which the Call waiting Supplementary Service is active.
1.4 Exceptional procedures or unsuccessful outcome
1.4.1 Incoming call from subscriber C ignored by subscriber B
If no response is received by the network from controlling subscriber B before the expiry of T2, then the network shall inform the controlling subscriber B that the call is no longer waiting. Subscriber C shall then be given a no reply indication, unless e.g. Call Forwarding applies. The call waiting service is then made available for a subsequent incoming call.
1.4.2 Incoming call from subscriber C is indicated as UDUB by subscriber B (or terminal B)
If the waiting call is indicated as UDUB by B before the expiry of T2 the subscriber C shall be given a busy indication, unless e.g. Call Forwarding applies. The call waiting service is then made available for a subsequent incoming call.
1.4.3 Release by subscriber C within the specified period
If calling subscriber C terminates the call attempt to subscriber B before the expiry of T2, the call attempt from C shall be terminated, as for basic call, and subscriber B shall be notified.
1.4.4 Incoming call from subscriber C is rejected by subscriber B
If the waiting call is explicitly rejected by B before the expiry of T2, the subscriber C shall be given a reject indication. The call waiting service is then made available for a subsequent incoming call.
1.5 Alternate procedures
1.6 Interactions with other Supplementary Services
22.214.171.124 Call forwarding unconditional
If call forwarding unconditional has been activated, it takes precedence over call waiting. Call forwarding unconditional can be activated while a call is waiting without changing the state of the waiting call.
126.96.36.199 Call forwarding on mobile subscriber busy
No impact, i.e. neither Supplementary Service shall affect the operation of the other Supplementary Service.
The following text clarifies the situation: If user B is NDUB (Network Determined User Busy), Call Forwarding shall take place, and the call is not offered to B. If B is not NDUB, the call shall be offered to B, and if the UDUB (User DUB) condition occurs, then the Call Forwarding shall take place.
188.8.131.52 Call forwarding on no reply
If the CFNRy is active and operative for the called subscriber then a waiting call shall still be offered as described in subclause 184.108.40.206 (call waiting indication). If no response is received to this call before the expiry of the No Reply Condition timer, then the call forwarding on no reply service becomes invoked and the call is forwarded as per that call forwarding on no reply service description.
220.127.116.11 Call hold
The served user may use the Call Hold service to answer subsequently a waiting call from C.
If the served mobile subscriber has an active call and a call one hold the network can still offer an incoming call with the waiting indication i.e. the NDUB condition is not used the normal way (n=2 not 1).
NOTE: Although the call is offered to the subscriber, she cannot accept the call as long as she has one active call and one call on hold.
If the served mobile subscriber has a call on hold and no active call, an incoming call is offered as a waiting call.
18.104.22.168 Calling line identification presentation
See TS 22.081 
See TS 22.084  .
22.214.171.124 Barring of all incoming calls
Invocation of Barring of Incoming Calls takes precedence over invocation of Call Waiting.
Call waiting cannot be activated if barring of incoming calls is activated. The mobile subscriber requesting for call waiting shall be informed of this Supplementary Service incompatibility. The activation of barring of incoming calls does not affect any currently waiting calls.
126.96.36.199 Barring of incoming calls when roaming outside the home PLMN country
When active and operative, same as interaction with Barring of All Incoming Calls.
1.7 Interactions with other services
See TS 22.135 .
1.8 Interworking considerations
Calls originating from outside the ISDN/PLMN can undergo call waiting at B.
A special in-band indication may be provided to the calling subscriber instead of the normal indication.