Session and Service Continuity Mode Selection Method
The SSC mode has the following selection methods:
-
The SMF verifies if UE sent SSC mode is part of either default ssc mode or allowed ssc mode in order of priority mentioned above. If it is found then PDU establishment procedure continues, otherwise PDU session establishment reject message will be sent to UE with allowed ssc modes in reject message.
-
If the SMF does not receive SSC mode from UE, then default ssc mode in the order of above priority is chosen and used to establish PDU session.
-
Since current release only supports SSC Mode-1, in case UE sends any other modes, PDU session establishment will be rejected.
Note | When UE requests SSC mode-2 or mode-3, as long as the UE's subscription (in the order of priority: UDM/Local configuration on SMF) allows SSC mode-1 along with SSC mode-2/3, SMF will send PDU session establishment reject with 5GSM cause: 68 (Not supported SSC mode) and Allowed SSC mode as 01. This approach is used to allow the UE to retry with SSC mode-1. As per 3GPP spec: 24.501, 5GSM cause: 68 to be sent when the requested SSC mode is not supported by the subscription. To honor PDU session establishment, SMF expects SSC mode either via UDM subscription or via local configuration. Otherwise, irrespective of SSC mode reception from UE, if SMF doesn't have SSC mode as part of UDM subscription or via local configuration, SMF would reject PDU session establishment with 5GSM cause: 31 (Request rejected and unspecified). |