Section: 5.15.4.2 Update of UE Network Slice configuration
Content: At any time, the AMF may provide the UE with a new Configured NSSAI for the Serving PLMN, associated with mapping of the Configured NSSAI to HPLMN S-NSSAIs as specified in clause 5.15.4.1. The Configured NSSAI for the Serving PLMN and the mapping information is either determined in the AMF (if based on configuration, the AMF is allowed to determine the Network Slice configuration for the whole PLMN) or by the NSSF. The AMF provides an updated Configured NSSAI as specified in clause 4.2.4 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3], UE Configuration Update procedure. If an S-NSSAI is to be stopped to be used, e.g. due to the network slice is to be deleted as described in TS 28.541[ Management and orchestration; 5G Network Resource Model (NRM); Stage 2 and stage 3 ]  [149], the AMFs may reject UE requests for the S-NSSAI based on the OAM state before the network slice becomes unavailable. The AMF may based on operator policies (e.g. when there is no timing information related to the termination or the AMF or UE does not support the timing information as described in in clause 5.15.16), release PDU Sessions associated with the S-NSSAI, and remove the S-NSSAI from e.g. the Allowed NSSAI and the Configured NSSAI before the Network Slice becomes unavailable. The AMF may use the timing information as described in clause 5.15.16 if it supports this feature and set validity time of the S-NSSAI accordingly. The AMF shall provide the UE with NSSRG information alongside the Configured NSSAI if NSSRG information is included in the subscription information received from the UDM and if the UE has indicated support for the feature as part of the registration request, see clause 5.15.12. The AMF may provide the UE with the mapping of old S-NSSAI to the Alternative S-NSSAI if the UE has indicated support for the feature as part of the registration request, see clause 5.15.19. If the HPLMN performs the configuration update of a UE registered in the HPLMN (e.g. due to a change in the Subscribed S-NSSAI(s) or due to a change of NSSRG information), this results in updates to the Configured NSSAI for the HPLMN and, if applicable, NSSRG information for each S-NSSAI of the Configured NSSAI. Updates to the Allowed NSSAI and/or, if present, to the associated mapping of the Allowed NSSAI to HPLMN S-NSSAIs are also possible if the configuration update affects S-NSSAI(s) in the current Allowed NSSAI. If the VPLMN performs the configuration update of a UE registered in the VPLMN (e.g. due to a change in the Subscribed S-NSSAI(s), the associated mapping is updated, or due to a change of NSSRG information), this results in updates to the Configured NSSAI for the Serving PLMN and/or to the associated mapping of the Configured NSSAI for the Serving PLMN to HPLMN S-NSSAIs and, if applicable, NSSRG information for each S-NSSAI of the Configured NSSAI. Updates to the Allowed NSSAI and/or to the associated mapping of the Allowed NSSAI to HPLMN S-NSSAIs are also possible if the configuration update affects S-NSSAI(s) in the current Allowed NSSAI. A UE for which the Configured NSSAI for the Serving PLMN has been updated as described in clause 5.15.4.1 and has been requested to perform a Registration procedure, shall initiate a Registration procedure to receive a new valid Allowed NSSAI (see clause 5.15.5.2.2). When the subscribed S-NSSAIs change, a UDR flag is set in the HPLMN to make sure the current PLMN (or, if the UE was not reachable, the next serving PLMN) is informed by the UDM that the subscription data for network slicing has changed. The AMF, when it receives the indication from the UDM subscription has changed, indicates the UE that subscription has changed and uses any updated subscription information from the UDM to update the UE. Once the AMF updates the UE and obtains an acknowledgment from the UE, the AMF informs the UDM that the configuration update was successful and the UDM clears the flag in the UDR. If the UE is in a CM-IDLE state, the AMF may trigger Network Triggered Service Request or wait until the UE is in a CM-CONNECTED state as described in clause 4.2.4.2, TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. If the UE receives indication from the AMF that Network Slicing subscription has changed, the UE locally deletes the network slicing information it has for all PLMNs, except the Default Configured NSSAI (if present). It also updates the current PLMN network slicing configuration information with any received values from the AMF. The update of URSP rules (which include the NSSP), if necessary at any time, is described in TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45].