Section: 5.15.15.2 UE Configuration of network-controlled Slice Usage Policy
Content: The UE during the Registration procedure may indicate in UE MM Core Network Capability that it supports UE configuration of network-controlled Slice Usage Policy. If so, the AMF determines Slice Usage Policy for one (or more) Network Slice(s) for the UE and configures the UE with this information together with Configured NSSAI to control the usage of this (or these) Network Slice(s). The AMF may be locally configured with network Slice Usage Policy, or receive the policy from the AM-PCF, or per the information received from UDM for AF managed timer values (see clause 5.15.15.3 for more details). The network-controlled Slice Usage Policy is provided to the UE in the Registration Accept or the UE Configuration Update Command and may include: - An indication, for one or more of S-NSSAI(s) of the HPLMN in the Configured NSSAI, whether the UE only registers with the Network Slice with the network when applications in the UE require data transmission in the Network Slice (i.e. the UE can only register the Network Slice only on demand and consider the Network Slice as on demand S-NSSAI). NOTE: All Other Network Slices in the Configured NSSAI are handled by the UE using UE specific policies (e.g. they may be registered irrespective of applications need). - For all on demand S-NSSAI(s) of the HPLMN in the Configured NSSAI, a deregistration inactivity timer that causes the UE to deregister the Network Slice after the last PDU Session associated with the S-NSSAI is released. This deregistration inactivity timer is started at the UE and AMF per access type when the last PDU Session associated with the S-NSSAI is released, or the Network Slice is included in the Allowed NSSAI and no PDU session is established. The deregistration inactivity timer is stopped and reset when the first PDU session is established or the S-NSSAI is removed from the Allowed NSSAI. The AMF and UE may locally remove the S-NSSAI from the Allowed NSSAI when the timer expires. The AMF may also send a UE Configuration Update Command to remove the slice from the Allowed NSSAI. If the UE and network state became misaligned, the UE may, for example, request connectivity in a Network Slice which is no longer allowed. In this case, the AMF shall provide the updated Allowed NSSAI in a UE Configuration Update Command after rejecting the PDU Session establishment. The UE may then re-register with the Network Slice if needed. The UE stores the received Slice Usage Policy with the Configured NSSAI for the serving PLMN and this is kept stored for as long as a Configured NSSAI remains stored for the PLMN. When the Configured NSSAI is updated, the AMF may also provide a new Slice Usage Policy to the UE. The AMF receives deregistration inactivity timer values as described in clause 5.15.15.3. If the slice deregistration inactivity timer value is updated, the AMF provides the updated value to the UE, if the UE supports UE configuration of network-controlled Slice Usage Policy, during the registration procedure (i.e. subsequent registration if there is no ongoing registration). The AMF and the UE, if the update been provided to the UE successfully, use the updated slice deregistration inactivity timer value next time the slice deregistration inactivity timer starts.