Section: 5.15.18.3 Network based monitoring and enforcement of Network Slice Area of Service not matching deployed Tracking Areas
Content: OAM may configure RRM policies for S-NSSAIs on a per cell basis as defined in TS 28.541[ Management and orchestration; 5G Network Resource Model (NRM); Stage 2 and stage 3 ]  [149], i.e. cells outside the Network Slice Area of Service while in a TA supporting the S-NSSAI are allocated with no RRM resources for the S-NSSAI. The network may enforce the NS-AoS for an S-NSSAI as follows: 1. The network may monitor the validity of the S-NSSAI for UE in CM-CONNECTED state, i.e. the AMF subscribes to the AoI using the Location information of the S-NSSAI location availability information as described in TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [34]. 2. If the non-supporting UE makes a PDU Session establishment request with an S-NSSAI that is not valid as per the S-NSSAI location availability information, the AMF may reject the NAS Transport message with a back-off timer using S-NSSAI based congestion control as described in clause 5.19.7.4. 3. If the AMF determines that the UE in CM-CONNECTED has moved outside the NS-AoS, the AMF performs the following logic: a) If the non-supporting UE has other S-NSSAI(s) in the Allowed NSSAI, then the AMF may update the UE with a UE Configuration Update by removing the S-NSSAI from the Allowed NSSAI (which causes the UE to locally release the PDU Sessions) and optionally removing the S-NSSAI from the Configured NSSAI and then, the AMF requests the SMF to locally release in the network any PDU Sessions with that S-NSSAI as per step 1f in clause 4.2.3.4 in TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. Alternatively, the AMF requests the SMF to release PDU Sessions with that S-NSSAI. b) If the non-supporting UE does not have any other S-NSSAI in the Allowed NSSAI, then the AMF may update the UE with a UE Configuration Update by removing the S-NSSAI from the Allowed NSSAI (which causes the UE to locally release the PDU Sessions) and optionally removing the S-NSSAI from the Configured NSSAI, and adding a default S-NSSAI to the Allowed NSSAI and then, the AMF requests the SMF to locally release in the network any PDU Sessions with the removed S-NSSAI as per step 1f in clause 4.2.3.4 in TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. Alternatively, the AMF requests the SMF to release PDU Sessions with that S-NSSAI. NOTE: Whether the AMF removes the S-NSSAI from Allowed NSSAI and Configured NSSAI or only releases the associated PDU Sessions when the AMF enforces the NS-AoS is up to AMF configuration. c) For a non-supporting UE that does not have any other S-NSSAI in the Allowed NSSAI nor in the Configured NSSAI, then the AMF indicates to the SMF to release the PDU Session. 4. If the AMF determines that the S-NSSAI becomes valid e.g. the UE has moved into the NS-AoS, the AMF may update the UE with a UCU e.g. including the S-NSSAI in the Configured NSSAI. 5. When the AMF determines that the S-NSSAI of a PDU Session is restricted to an NS-AoS in the PDU session, the AMF indicates to the SMF that the PDU Session is subject to area restriction for the S-NSSAI. As a result, the SMF subscribes to "UE mobility event notification" for reporting UE presence in Area of Interest by providing S-NSSAI to the AMF as described in clauses 5.6.11 and 5.3.4.4. When SMF is notified that the UE location is outside of Area of Interest, SMF shall not send user data as payload of NAS message (see clause 5.31.4.1) in downlink directions and disable data notification. 6. When the SMF is notified by the AMF that the UE location is UNKNOWN as defined in Annex D, clauses D.1 and D.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3], then based on operator policy SMF may enable downlink data notification and trigger the Network triggered Service Request procedure to active the UP connection or send user data as payload of a NAS message (see clause 5.31.4.1) when the SMF receives downlink data or Data Notification from UPF. Editor's note: Whether and based on what criteria to trigger the reporting and the applicability to the CP CIOT optimization use cases are FFS.