B.4 Early call forwarding on busy

03.793GPPStage 2Support of Optimal Routeing phase 1TS

The Provide Subscriber Information procedure would allow the NDUB status of the called subscriber to be determined, so that call forwarding on busy would be possible before the call has been extended to VMSCB. For consistency of handling, this would also require an enhancement to the handling of the Provide Roaming Number handling, so that if the B subscriber is busy VLRB would return a busy subscriber negative response to the Provide Roaming Number, and call forwarding on busy could be triggered at the HLR. This would also require changes to the stage 1, 2 & 3 specifications for the call forwarding on busy service.