UDM-Initiated Deregistration Call Flow

This section describes the UDM-Initiated Deregistration call flow.

The UDM starts the deregistration process for an UE if the subscription is withdrawn for the UE. The UDM starts this procedure for operator-determined purposes to request the removal of a subscriber's RM context and PDU sessions of the UE.

UDM-Initiated Deregistration Call Flow
UDM-Initiated Deregistration Call Flow Description

Step

Description

1

If the UDM wants to request the immediate deletion of a subscriber's contexts and PDU sessions, the UDM sends a Nudm_UECM_DeregistrationNotification (SUPI, Access Type, Removal Reason) message with Removal Reason set to Subscription Withdrawn to the registered AMF. If the AMF receives Nudm_UECM_DeregistrationNotification with Removal Reason as Subscription Withdrawn, the AMF executes the deregistration procedure over the access.

2

The AMF may explicitly deregister the UE by sending a Deregistration Request message (Deregistration type, Access Type) to the UE. The deregistration type may be set to Reregistration in which case the UE should reregister at the end of the deregistration procedure. 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.

3

If the deregistration procedure is triggered by UDM, the AMF acknowledges the Nudm_UECM_DeRegistrationNotification to the UDM.

4

The AMF unsubscribes with the UDM using Nudm_SDM_Unsubscribe service operation.

5, 6

If the UE has any established PDU sessions, the UE-initiated Deregistration is performed.

7

If there is any association with the PCF for this UE and the UE is no more registered over any access, the AMF performs a AMF-initiated AM Policy Association Termination procedure

8

If the UE receives the Deregistration Request message from the AMF, the UE sends a Deregistration Accept message to the AMF. The NG-RAN forwards this NAS message to the AMF along with the TAI and cell identity of the cell which the UE is using.

9

The AMF exchanges the N2 UE Context Release with gNB.