Abstract: A method of enhancing session continuity for system interworking is proposed. Upon intersystem change from S1 mode to N1 mode, a UE may perform deregistration when re-registration is required. The UE stops all 5GSM non-congestion back-off timers. In addition to the 5GSM non-congestion back-off timers, there may be ESM non-congestion back-off timers running. The UE may take the RATC and the EPLMNC indicators in the Re-attempt indicator IE into consideration, and stops all ESM non-congestion timers. Upon intersystem change from N1 mode to S1 mode, the UE may perform detach procedure when re-attach is required. The UE stops all ESM non-congestion back-off timers. In addition to the ESM non-congestion back-off timers, there may be 5GSM non-congestion back-off timers running. The UE may take the RATC and the EPLMNC indicators in the Re-attempt indicator IE into consideration, and stops all 5GSM non-congestion timers.

Abstract: A method of enhancing session continuity for system interworking is proposed. Upon a UE performs inter-system change from A/Gb mode or Iu mode to S1 mode, the UE identifies that some PDN connection(s) are not associated with a PDU session ID (PSI). In one novel aspect, the UE deactivates all EPS bearer contexts for such PDN connection(s) locally, includes the EPS bearer context status IE in a TRACKING AREA UPDATE REQUEST message of a tracking area updating (TAU) procedure upon inter-system change from A/Gb mode or Iu mode to S1 mode, and then initiates UE requested PDN connectivity procedure(s) for such PDN connection(s). Furthermore, if no EPS bearer exists after local deactivation and EMM-REGISTERED without PDN connection is not supported by the UE, then the UE initiates a re-attach procedure followed by the UE requested PDN connectivity procedure(s) for such PDN connection (s) .