Section: 4.6.2.9 Mobility management based network slice usage control
Content: If the UE and the network support network slice usage control, the AMF monitors network slice usage by running a slice deregistration inactivity timer per S-NSSAI and access type. The AMF may also provide on-demand NSSAI to the UE in the REGISTRATION ACCEPT message or in the CONFIGURATION UPDATE COMMAND message. The on-demand NSSAI consists of one or more on-demand S-NSSAIs and, optionally, the slice deregistration inactivity timer per on-demand S-NSSAI. The slice deregistration inactivity timer is: a) started when there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type; and b) stopped and reset when at least a PDU session, including any MA PDU session, associated with the S-NSSAI is successfully established over the corresponding access type(s) or the S-NSSAI is removed from the allowed NSSAI. If the slice deregistration inactivity timer value is updated, the AMF updates the stored timer value and may provide the updated timer value to the UE in the REGISTRATION ACCEPT message or the CONFIGURATION UPDATE COMMAND message. When the UE receives an updated slice deregistration inactivity timer value in the REGISTRATION ACCEPT message or the CONFIGURATION UPDATE COMMAND message from the AMF, the UE updates the stored timer value. Upon expiry of the slice deregistration inactivity timer, the AMF locally removes the S-NSSAI from the allowed NSSAI over the access type. In addition, the AMF may send the CONFIGURATION UPDATE COMMAND message to the UEs with the new allowed NSSAI. The UE includes the on-demand S-NSSAI which the UE requests in the requested NSSAI during the registration procedure. Upon expiry of the slice deregistration inactivity timer, the UE locally removes the S-NSSAI from the allowed NSSAI over the access type. If the UE supports network slice usage control, the AMF provides on-demand NSSAI in the Configured NSSAI to the UE in the REGISTRATION ACCEPT message or in the UE Configuration Update Command message. The on-demand NSSAI consists of one or more configured S-NSSAIs. The on-demand S-NSSAI(s) is deleted by the UE from the stored on-demand NSSAI, when the associated configured S-NSSAI(s) is deleted by the UE from the stored configured NSSAI. NOTE: The network slice usage control feature is not supported in roaming scenarios.