AMF-Initiated Deregistration Call Flow

This section describes the AMF-Initiated Deregistration call flow.

If implicit detach timer expires, the AMF performs deregistration.

AMF-Initiated Deregistration Call Flow

In case of a clear subscriber, the AMF starts a deregistration procedure.

AMF-Initiated Deregistration Call Flow Description

Step

Description

1

If the PDU session is established, the AMF sends Nsmf_PDUSession_ReleaseSMContext (SUPI, PDU, and Session ID) to SMF. All PDU sessions over the target access, which belong to the UE are released by the AMF by sending Nsmf_PDUSession_ReleaseSMContext Request (SUPI, PDU Session ID) message to the SMF for each PDU Session.

2

The SMF releases all resources (for example, the IP address/Prefixes that were allocated to the PDU Session) and the corresponding User Plane resources. The SMF responds with Nsmf_PDUSession_ReleaseSMContext Response message.

3

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

4

The AMF unsubscribes the UDM using the Nudm_SDM_Unsubscribe service operation.

5

The AMF invokes the Nudm_UECM_Deregistration service operation so that the UDM removes the association it had stored.

6

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.

7

After 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.

8

The AMF and gNB exchanges the N2 UE Context Release.