Section: 4.2.2.3.3 Network-initiated Deregistration
Content: The procedure depicted in Figure 4.2.2.3.3-1 shows Network-initiated Deregistration procedure. The AMF can initiate this procedure for either explicit (e.g. by O&M intervention or if the AMF determines that no S-NSSAI can be provided in the Allowed NSSAI for the UE or the UE's registered PLMN is not allowed to operate in the present UE location or if a disaster condition is no longer being applicable, the AMF initiates Network-initiated Deregistration to trigger the return of UEs to the PLMN that had a Disaster Condition) or implicit (e.g. expiring of Implicit Deregistration timer). The UDM can trigger this procedure for operator-determined purposes (e.g. if a disaster condition is no longer being applicable as specified in clause 5.40.5 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]) to request the removal of a subscriber's RM context and PDU Session(s) of the UE. If the Network-initiated Deregistration procedure is triggered for MBSR IAB-UE that is registered with authorization to act as MBSR, the AMF behaves as described in clause 5.35A.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. Figure 4.2.2.3.3-1: Network-initiated Deregistration 1. [Conditional] If the UDM wants to request the immediate deletion of a subscriber's RM contexts and PDU Sessions, the UDM shall send a Nudm_UECM_DeregistrationNotification (SUPI, Access Type, Removal Reason) message with Removal Reason set to Subscription Withdrawn to the registered AMF. The Access Type may indicate 3GPP Access, non-3GPP Access or both. 2. If the AMF receives Nudm_UECM_DeregistrationNotification in Step 1 with Removal Reason as Subscription Withdrawn, the AMF executes Deregistration procedure over the access(es) the Access Type indicates. The AMF-initiated Deregistration procedure is either explicit (e.g. by O&M intervention or if the AMF determines that no S-NSSAI can be provided in the Allowed NSSAI for the UE) or implicit. The AMF does not send the Deregistration Request message to the UE for Implicit Deregistration. If the UE is in CM-CONNECTED state, the AMF may explicitly deregister the UE by sending a Deregistration Request message (Deregistration type, Access Type, [list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value]) to the UE. The Deregistration type may be set to Re-registration in which case the UE should re-register at the end of the Deregistration procedure. Access Type indicates whether Deregistration procedure applies to the 3GPP access or non-3GPP access, or both. If the Deregistration Request message is sent over 3GPP access and the UE is in CM-IDLE state in 3GPP access, the AMF pages the UE. The list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value, is provided if the AMF determines that no S-NSSAI can be provided to the UE in the Allowed NSSAI. If the UE has established PDU Session associated with emergency service, the AMF shall not initiate Deregistration procedure. In this case, the AMF performs network requested PDU Session Release for any PDU session associated with non-emergency service as described in clause 4.3.4. For NR satellite access, the AMF initiates Network-initiated Deregistration if it detects that the UE's registered PLMN is not allowed to operate in the present UE location. In this case, the AMF shall provide the appropriate cause value indicating the PLMN is not allowed to operate in the present UE location, see clause 5.4.11.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If the network de-registration is triggered for a UE registered for Disaster Roaming due to a disaster condition no longer being applicable, the Deregistration Request shall contain the cause value "PLMN not allowed" and include a disaster return wait range as described in clause 5.5.2.3.1 of TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [25] and as specified in clause 5.40.5 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], the network, shall organise the return of the Disaster Roaming UEs in a manner that does not cause overload (e.g. of signalling) in the PLMN that previously had the Disaster Condition. If the MBSR authorization state changes for a MBSR (IAB-UE) registered in network as specified in clause 5.35A.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], based on operator configuration, the AMF triggers Deregistration procedure. 3. [Conditional] If the Deregistration procedure is triggered by UDM (Step 1), the AMF acknowledges the Nudm_UECM_DeRegistrationNotification to the UDM. If Access Type indicates 3GPP Access or non-3GPP Access and AMF does not have UE context for another access type, or if Access Type indicates both, the AMF unsubscribes with the UDM using Nudm_SDM_Unsubscribe service operation. 4. [Conditional] If the UE has any established PDU Session over the target access for deregistration indicated in step 2, then step 2 ~ step 5 of UE-initiated Deregistration procedure in clause 4.2.2.3.2 is performed. 5. [Conditional] As in step 6 of Figure 4.2.2.3.2-1. 5a. [Conditional] As in step 6a of Figure 4.2.2.3.2-1. 6. [Conditional] If the UE receives the Deregistration Request message from the AMF in step 2, the UE sends a Deregistration Accept message to the AMF any time after step 2. The NG-RAN forwards this NAS message to the AMF along with the TAI+ Cell identity of the cell which the UE is using. 7. [Conditional] AMF to AN: N2 UE Context Release Request (Cause): as in step 8 of Figure 4.2.2.3.2. If the UE is deregistered over only 3GPP access or non-3GPP access and the AMF does not have UE context for the other, or if the procedure applies to both access types, then at any time, AMF can unsubscribe from the UDM, otherwise the AMF can deregister from UDM using Nudm_UECM_Deregistration request by indicating its associating access type.