Abstract: In 5GS, Single-Network Slice Selection Assistance Information (S-NSSAI) based backoff (BO) timers (T3585) can be applied to either 3GPP access or non-3GPP access or both access based on a 5GSM congestion re-attempt indicator. When UE receives a 5GSM message over a specific access, UE needs to handle a current running timer. In one novel aspect, it is proposed that the UE stops the running timer applied for the same access which the message is received, and also stops the running timer applied for both access types. In another novel aspect, it is proposed that the UE stops the running timer applied for the access different from the access which the message is received when the UE starts a new timer applied for both access types.

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) .

Abstract: A method for 5G Session Management (5GSM) handling of network rejection not due to congestion control is provided. A User Equipment (UE) receives a 5GSM reject message from a mobile communication network. The 5GSM reject message indicates a network rejection not due to congestion control. The UE associates a back-off timer with a Home Public Land Mobile Network (HPLMN) Single-Network Slice Selection Assistance Information (S-NSSAI). The UE prevents itself from sending a 5GSM request message for the same HPLMN S-NSSAI that is associated with the back-off timer.

Abstract: In 5GS, Single-Network Slice Selection Assistance Information (S-NSSAI) based backoff (BO) timers (T3584/T3585) can be applied to either the registered PLMN or all the PLMNs based on a 5GSM congestion re-attempt indicator. For a specific PDU session, the corresponding BO timer applied to the registered PLMN and the BO timer applied to all PLMN can be both running concurrently. It is proposed for a UE to stop both the BO timer applied to all the PLMNs and the BO timer applied to the registered PLMN, if running, in all the following scenarios: 1) Receiving a PDU session release command without a BO timer, 2) Receiving a PDU session release command with 5GSM cause #39, 3) Receiving a PDU session modification command, 4) Receiving a 5GSM message with a 5GSM congestion control BO timer value, and 5) Receiving a PDU session authentication command.

Abstract: A method of handling a Packet Data Network (PDN) connection to support interworking to 5G system (5GS) is proposed. In a first novel aspect, both UE and the network stores mapped 5GSM parameters of a corresponding Protocol Data Unit (PDU) session when inter-system change from S1 (4G, EPS) mode to A/Gb (2G) mode or Iu (3G, UMTS) mode. In a second novel aspect, the PDN connection is enable to support interworking to 5GS, and the UE is allowed to allocate and indicate the PDU session ID by using the bearer resource modification procedure in EPS, or the mapped 5GSM parameters can be provided and modified in 2G/3G system.

Abstract: A method of handling a Packet Data Network (PDN) connection to support interworking to 5G system (5GS) is proposed. In a first novel aspect, both UE and the network stores mapped 5GSM parameters of a corresponding Protocol Data Unit (PDU) session when inter-system change from S1 (4G, EPS) mode to A/Gb (2G) mode or Iu (3G, UMTS) mode. In a second novel aspect, the PDN connection is enable to support interworking to 5GS, and the UE is allowed to allocate and indicate the PDU session ID by using the bearer resource modification procedure in EPS, or the mapped 5GSM parameters can be provided and modified in 2G/3G system.