5 Normal procedures with successful outcome

22.0933GPPCompletion of Calls to Busy Subscriber (CCBS)Release 17Service description, Stage 1TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.1 Provision

5.1.1 Subscriber A

The CCBS supplementary service shall be provided to subscriber A after prior arrangement with the service provider.

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 BSs.

5.1.2 Subscriber B

Subscriber B is the user of destination B and is not provided with the CCBS supplementary service. However, if provided by the network operator/service provider as an option, subscriber B may elect not to be a target of CCBS requests. In this case, the size of her destination B CCBS queue shall be reduced to zero length by the service provider. Only the service provider may subsequently change the destination B CCBS queue length on demand of subscriber B.

5.2 Withdrawal

The CCBS supplementary service shall be withdrawn at the customer’s request or for administrative reasons. At the same time, all outstanding CCBS requests shall be automatically deactivated.

5.3 Registration

Not applicable.

5.4 Erasure

Not applicable.

5.5 Activation

The CCBS service shall be activated as a result of provisioning.

A CCBS request shall be activated by the mobile subscriber on a per-call basis by a control procedure as described in TS 22.030 [3].

When subscriber A encounters a NDUB destination B, the network shall retain the call information for a period defined by the CCBS retention timer (T1), and inform subscriber A that CCBS is possible when the following set of conditions apply:

– subscriber A has the CCBS supplementary service provisioned;

– the call failure reason is either "user busy or "no circuit/channel available";

– CCBS is available (as determined by network B as described below).

During this time subscriber A can activate the CCBS request.

CCBS is available at network B, when the following set of conditions apply:

– network B supports the CCBS supplementary service;

– destination B is found to be NDUB; and

– the maximum length of destination B’s CCBS queue is greater than zero.

If the network accepts the activation of a CCBS request the network shall register the call information in the original call request, and subscriber A shall be informed that the activation was successful.

When the activation of a CCBS request is accepted the CCBS service duration timers (T3 and T7) are started. The network shall monitor destination B for destination B becoming idle.

Subscriber A can have a limited number of CCBS requests outstanding. This limit is a network option (with a maximum value of 5). The CCBS requests can be to different destination Bs, or can be to the same destination B with different basic service requirements.

Destination B can have a limited number of incoming CCBS requests outstanding. This limit is a network option (with a maximum value of 5). The requests can be from different subscriber As, or can be from the same subscriber A with different basic service requirements.

Having activated a CCBS, subscriber A can originate calls and receive calls as normal.

5.6 Deactivation

The CCBS supplementary service shall be deactivated as a result of withdrawal.

A previous CCBS request activation shall be deactivated by the mobile subscriber by a control procedure as described in TS 22.030 [3] or shall be automatically deactivated after a successful CCBS procedure or for exceptional situations as described in subclause 6.4.

Deactivation of a CCBS request shall result in all reference to this CCBS request (entries in A and B queue and timers) being removed from the network.

Subscriber A can send the following deactivation request:

a) deactivate all outstanding CCBS requests;

b) deactivate one specific CCBS request.

Subscriber A shall be informed that the deactivation is successful.

5.7 Invocation and operation

The CCBS supplementary service shall be automatically invoked by the network after destination B has become idle.

When destination B is or becomes idle or reachable and there are non-suspended CCBS requests in destination B’s CCBS queue, then the network shall start the destination B idle guard timer (T8).

When the destination B idle guard timer (T8) expires and destination B is still idle, the first non-suspended CCBS request shall be processed, provided that an entry in the destination B’s CCBS queue is not currently being processed. Entries shall not be processed in parallel. This means that the CCBS recall procedure shall be started towards subscriber A, informing subscriber A that destination B is now idle and the CCBS recall B timer (T9) shall be started.

If subscriber A is idle or not CCBS busy, subscriber A shall be recalled with an indication that it is a CCBS recall and with an indication of which CCBS request it applies to, and the CCBS recall timer (T4) shall be started. Optionally, the ME may use a specific alert (e.g. a tone, different from the one used for normal MT call) for the indication of a CCBS recall.

If subscriber A accepts the recall before the CCBS recall timer (T4) expires, then the network shall initiate the CCBS call to destination B using the call information of the original call set-up (retained in the network). When the network receives an indication that the destination B is being informed of the CCBS call, the corresponding CCBS request shall be considered as completed.

Whilst the destination B idle guard timer (T8) is running, and also whilst awaiting the CCBS call to destination B (whilst CCBS recall B timer (T9) is running), a new incoming call shall not be offered to destination B. For such incoming calls, the called user shall be considered as being NDUB and the calling user shall be informed as for basic call procedures.

The CCBS requests in the destination B CCBS queue shall be processed in the order they are received, although the actual mechanism for processing the CCBS queue is outside the scope of the present document. During the processing of the destination B CCBS queue, CCBS requests which are currently suspended shall be ignored and the next entry in the CCBS queue shall be processed.

If, for any reason, no CCBS call results from the processing of a CCBS request, then provided destination B is still idle, the next CCBS request in the destination B CCBS queue shall be selected for processing. This procedure shall be repeated until the processing of the destination B CCBS queue is complete.

If all of the destination B CCBS queue has been processed and no CCBS call results, then processing is complete.

5.8 Interrogation

Subscriber A can request the list of the CCBS requests by a control procedure as described in TS 22.030 [3]. In response to the request subscriber A shall be given a list of the addresses and basic services against which CCBS requests are outstanding.