This TS specifies the stage 1 description of Completion of Calls to Busy Subscriber (CCBS) from the subscriber's and user's points of view.
Here is a short description of the CCBS service:
When subscriber A encounters a Network Determined User Busy (NDUB) destination B, subscriber A can request the CCBS supplementary service (i.e. activate a CCBS Request against destination B). The network will then monitor the wanted destination B for becoming idle.
When the wanted destination B becomes idle, then the network will wait a short time in order to allow destination B to make an outgoing call. If destination B does not make any outgoing call within this time, then the network shall automatically recall subscriber A.
When subscriber A accepts the CCBS recall, within a defined time, then the network will automatically generate a CCBS call to destination B.
CCBS has to be supported by the originating, as well as by the terminating network.