Network-initiated PDU Session Release Call Flow

The network-initiated PDU session release procedure allows the AMF, the SMF or the PCF to initiate the release of a PDU session.

The following figure depicts the network-initiated PDU session release call flow.

Network-initiated PDU Session Release Call Flow
Network-initiated PDU Session Creation Call Flow Description
Step Description
1

This procedure can be triggered by PCF, CHF, UDM, UPF or CLI (clear subscriber) to initiate the release of a PDU session.

2, 3

The SMF sends N4SessionReleaseRequest to the UPF. The UPF sends response for the same.

Note

Skip the steps 4 to 14 if the AMF has notified that the UE is not reachable.

4

The SMF sends N1N2MessageTransfer message with N11, N1 and N2 content.

  • N11: SkipInd=True

  • N1: PDU_SESSION_RELEASE_COMMAND

  • N2: N2_PDU_SESSION_RESOURCE_RELEASE_COMMAND. exclude if the SMF is in IDLE mode. Also, skip the steps 8, 9, and 10.

5

The AMF responds back to the SMF with the cause included in the N1N2MessageTransferRsp message.

Note

Skip the steps 6 to 14 if the AMF sends the cause as N1_MSG_NOT_TRANSFERRED in step 5.

6, 7

The AMF exchanges the message with RAN. The RAN forwards it to the UE.

8, 9, 10

The RAN sends N2 release response to the AMF. The AMF transfers N2 release response (N2_PDU_SESSION_RESOURCE_RELEASE_RESPONSE_TRANSFER) in N11 SmContextUpdateRequest message. The SMF responds back to the AMF as SmContextUpdateResponse.

11, 12, 13, 14

The UE sends N1 release response in the NAS message to the AMF through the RAN. The AMF sends the N1 release response (PDU_SESSION_RELEASE_COMPLETE) in N11 SmContextUpdateRequest message. The SMF responds back to the AMF as SmContextUpdateResponse.

15, 16

The SMF sends delete charging request to the CHF. The CHF responds back to the SMF with delete response.

17, 18

The SMF sends SmContextStausNotify to the AMF. The AMF responds back with the SmContextStausNotifyResponse message.

19, 20

The SMF sends delete request to the PCF. The PCF responds back to the SMF with delete response.

21, 22

The SMF sends UDM deregistration request. The UDM responds back to the SMF with deregistration response.