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1: UDM -> AMF
-> [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(SUPI, Access Type, Removal Reason) message with Removal Reason set to Subscription Withdrawn to the registered AMF.
2: AMF -> UE
-> 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.
3: AMF -> UDM
-> [Conditional] If the Deregistration procedure is triggered by UDM (Step 1), the AMF acknowledges the Nudm_UECM_DeRegistrationNotification to the UDM.
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 is performed.
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.
7:
-> [Conditional] AMF to AN: N2 UE Context Release Request (Cause): as in step 8
TS 23.502