SMF-Initiated PDU Release Call Flow
This section describes the SMF-Initiated PDU Release call flow.
The PDU Session Release procedure is used to release all the resources associated with a PDU session.

Step |
Description |
---|---|
1 |
If the UP connection of the PDU session is active, the SMF includes the N2 Resource Release Request (PDU Session ID) in the Namf_Communication_N1N2MessageTransfer, to release the RAN resources associated with the PDU session. |
2 |
The SMF responds to the AMF with the Nsmf_PDUSession_ReleaseSMContext response. |
3 |
The AMF transfers the SM information received from the SMF (N2 SM Resource Release request, N1 SM container) to the RAN. |
4 |
When the RAN has received an N2 SM request to release the AN resources associated with the PDU session, it issues AN-specific signaling exchanges with the UE to release the corresponding AN resources. |
5 |
The RAN sends any NAS message (N1 SM container (PDU Session Release Command)) received from the AMF. |
6 |
The AMF invokes the Nsmf_PDUSession_UpdateSMContext (N2 SM Resource Release Ack, User Location Information) to the SMF. |
7 |
The SMF responds to the AMF with an Nsmf_PDUSession_UpdateSMContext response. |
8 |
The UE acknowledges the PDU Session Release Command by sending a NAS message (PDU Session ID, N1 SM container (PDU Session Release Ack)) message over the RAN. |
9 |
The RAN forwards the NAS message from the UE by sending a N2 NAS uplink transport (NAS message (PDU Session ID, N1 SM container (PDU Session Release Ack)), User Location Information) to the AMF. |
10 |
The AMF invokes the Nsmf_PDUSession_UpdateSMContext (N1 SM container (PDU Session Release Ack, User Location Information) to the SMF. |
11 |
The SMF responds to the AMF with an Nsmf_PDUSession_UpdateSMContext response. |
12 |
The SMF invokes Nsmf_PDUSession_SMContextStatusNotify to notify AMF that the SM context for this PDU session is released. The AMF releases the association between the SMF ID and the PDU Session ID, DNN, and S-NSSAI. |