3 Definitions and abbreviations
22.0933GPPCompletion of Calls to Busy Subscriber (CCBS)Release 17Service description, Stage 1TS
3.1 Definitions
For the purposes of the present document, the following definitions apply:
CCBS supplementary service: is a service which enables a calling subscriber A, encountering a NDUB destination B, to have the call completed when the busy destination B becomes idle, without having to make a new call attempt.
CCBS busy on the A side: is caused by the following condition:
– while the CCBS recall timer T4 or the CCBS notification timer T10 is running or until the CCBS call is completed or the CCBS call fails.
CCBS busy on the B side: is caused by the following conditions:
– while the idle guard timer (T8) is running;
– while there is CCBS recall pending (i.e. while the CCBS recall timer T9 is running).
Subscriber A and Destination B is indicated as idle if there are no active calls, no calls on hold and no call waiting for the subscribers.
Subscriber A and Destination B is indicated as not reachable if one of the conditions defined in TS 29.002 [4] apply (e.g. IMSI detach, no paging response, no location information in HLR).
CCBS recall: an indication informing subscriber A that destination B is idle.
CCBS call: a call set-up from subscriber A to destination B resulting from subscriber A’s acceptance of a CCBS recall.
CCBS request: A request by subscriber A against an NDUB destination B requesting that subscriber A be automatically informed when destination B becomes idle. The CCBS request shall be held in a CCBS queue pending the correct conditions for the CCBS request to be completed.
Destination B: the entity addressed in the original call set up.
Subscriber A: the subscriber that originated the call, activated a CCBS request and is uniquely identifiable for CCBS recall.
Suspended CCBS request: a CCBS request which cannot be served even if destination B is idle, because subscriber A is CCBS busy, not reachable or is not idle and ignores the CCBS recall.
Resumed CCBS request: a CCBS request which was suspended before and has become not suspended as a result of subscriber A becoming idle, not CCBS busy or reachable again.
Automatic deactivation: an action by the network resulting in removal of all reference to a CCBS request without informing the subscriber. Automatic deactivation is performed after a successful CCBS procedure or for exceptional situations.
Timers at the originating side (A):
CCBS retention timer (T1): this timer specifies the amount of time that the network retains the call information when the call encounters busy. The value shall be greater than 15 seconds. The upper limit of the CCBS retention timer is a network option.
CCBS service duration timer (T3): the maximum time the CCBS request will be active within the network. The value of this period is a network option, in the range of 15 to 45 minutes.
CCBS recall timer (T4): the maximum time the network will wait for a subscriber A response to a CCBS recall when subscriber A is idle. The value of this timer is a network option and shall be in the range 20 to 30 seconds.
CCBS notification timer (T10): the maximum time the network will wait for a subscriber A response to a CCBS recall when subscriber A is not idle and not CCBS busy. The value of the timer is a network option and shall be in the range 20 to 30 seconds.
CCBS resume timer (T11): the timer started as soon as a suspended CCBS request is resumed, making sure only one CCBS request is becoming resumed at a time. Duration of the timer shall allow a CCBS recall resulting from the destination side CCBS queue being processed. The value of the timer is a network option and shall be in the range 20 to 25 seconds.
Timers at the terminating side (B):
CCBS service duration timer (T7): is the timer which specifies the maximum length of time the CCBS request will be held within the network. The value of this period is a network option shall be greater than 45 minutes.
Destination B idle guard timer (T8): the time the network will wait after destination B has become idle before initiating a "CCBS recall" to subscriber A. The value of this timer is a network option and shall be in the range 0 to 15 seconds.
NOTE 1: This timer enables destination B to initiate a call before any notification is given to subscriber A that destination B has become idle and prevents destination B to receive incoming calls.
CCBS recall B timer (T9): is the timer, which supervises the CCBS recall establishment on the B-side. The value is a network option and shall be shall be in the range of 40 to 55 seconds.
NOTE 2: This timer prevents destination B from receiving other incoming calls than from subscriber A.
NOTE 3: The timer values may vary from one PLMN to another and thus give the subscriber a slightly different perception of the service as she roams between PLMN’s.
3.2 Abbreviations
For the purposes of the present document the following abbreviations apply:
CCBS Completion of Calls to Busy Subscriber
NDUB Network Determined User Busy
Additional abbreviations may be found in GSM 01.04 [1] and TR 21.905 [6].