03.933GPPStage 2Technical realization of Completion of Calls to Busy Subscriber (CCBS)TS
GSM 02.93 specifies a number of interactions between CCBS and other network features.
9.1 Customised Applications for Mobile network Enhanced Logic (CAMEL)
For a terminating CAMEL based service which changes the destination B address for the original call which subsequently encounters NDUB, the GMSC shall inform originating network that CCBS is not possible when it releases the call.
If an originating CAMEL based service determines for a CCBS Call a different destination B Address than for the original call, the CCBS Call shall be released and the associated CCBS Request shall be cancelled.
If the CAMEL based service requests a call set-up to an alternative destination after the original call has met Busy, CCBS Possible condition, the CCBS activation shall be allowed if the alternative call set-up also encounters Busy condition.
9.2 Support of Optimal Routeing (SOR)
The CCBS supporting GMSC shall include CCBS Supported indicator to the SRI message.
If HLR B receives a request for routeing information when destination B is blocked (i.e. the HLR B is waiting for an SRI for a CCBS call set-up) and the SRI does not include a CCBS call indicator nor CCBS supported in the GMSC indicator and the request is from a GMSC not in the same PLMN as HLR B, then HLR B shall return an SRI negative response indicating OR not allowed. This will force the GMSC to route the call to a GMSC in the same PLMN as HLR B (see GSM 03.79).
The GMSC in HPLMN B should be able to include the CCBS Call indicator in the non-OR SRI, and the CCBS call set-up will proceed, although it won’t be optimally routed.
If the HLR receives an SRI indicating a CCBS-capable GMSC but not a CCBS call while awaiting SRI for a CCBS call, it can treat the request as if the B-subscriber were busy, regardless of where the GMSC is.