B.3 Reject SRVCC due to UE call state incompatibility

23.2373GPPIP Multimedia Subsystem (IMS) Service ContinuityRelease 17Stage 2TS

Additional enhancement may be applied to avoid unsuccessful SRVCC. If supported, this procedure enables the MSC server to decide whether to proceed or not proceed with SRVCC.

In order to enable the MSC server to decide whether to proceed with SRVCC or not for the current session, IMS needs to indicate to the MSC server if IMS supports SRVCC in pre-Alerting or Alerting state and the actual state of the call. If SRVCC at this stage of the call is not possible (e.g. due to the call being in Pre-Alerting or Alerting), then the MSC server shall not proceed with SRVCC.

NOTE: Stage 3 may specify different solutions; one that can be part of the codec inquiry and is used with that option while the other one can be within other procedure for SRVCC.

Annex C (Normative):
ATCF in Architectures without IMS-level roaming interfaces