Section: 4.6.3.4 Session management based network slice replacement
Content: If: a) the UE and network support network slice replacement; b) the UE is provided with the mapping information between the S-NSSAI to be replaced and the alternative S-NSSAI; and c) the UE decides to establish a new PDU session with the S-NSSAI to be replaced, the UE provides both the S-NSSAI to be replaced and the alternative S-NSSAI during PDU session establishment procedure. If the timer T3584 or timer T3585 is running for the S-NSSAI to be replaced, the UE should not stop the timer during PDU session establishment procedure. If the SMF receives both the S-NSSAI to be replaced and the alternative S-NSSAI during PDU session establishment procedure, the SMF proceeds with the PDU session establishment procedure with the alternative S-NSSAI. If the PDU session establishment request is accepted, the SMF includes the alternative S-NSSAI in the PDU session establishment accept message. If the UE is provided with the mapping of the VPLMN S-NSSAI to a VPLMN alternative S-NSSAI, the UE provides both the VPLMN alternative S-NSSAI and the VPLMN S-NSSAI in the PDU SESSION ESTABLISHMENT REQUEST message. If the UE is provided with the mapping of the HPLMN S-NSSAI to a HPLMN Alternative S-NSSAI, the UE provides both the HPLMN alternative S-NSSAI and the HPLMN S-NSSAI in the PDU SESSION ESTABLISHMENT REQUEST message. The AMF sends both HPLMN alternative S-NSSAI and HPLMN S-NSSAI to the SMF. If the SMF receives from the AMF an alternative S-NSSAI for existing PDU session and: a) if the SMF decides to retain the existing PDU session (i.e. the SMF can serve both the alternative S-NSSAI and the S-NSSAI to be replaced with), the SMF sends the alternative S-NSSAI to the UE during network-requested PDU session modification procedure; or b) if the SMF decides to re-activate the existing PDU session and: 1) if the SSC mode of the PDU session is SSC mode 3, the SMF initiates PDU session modification procedure to trigger PDU session reactivation by the UE; or 2) if the SSC mode of the PDU session is SSC mode 1 or SSC mode 2, the SMF initiates PDU session release procedure to trigger PDU session reactivation by the UE. If the timer T3584 or timer T3585 is running for the S-NSSAI that was replaced and the S-NSSAI that was replaced in alternative NSSAI is available and the AMF provides the updated allowed NSSAI and configured NSSAI to the UE, the UE should stop the timer.