AMF-initiated PDU Session Release with N11 Release=True

The AMF-initiated PDU session release procedure allows the AMF to initiate the release of a PDU session with the N11 release in the SmContextModifyRequest being set to True.

The following figure depicts the AMF-initiated PDU session release call flow with the N11 release=True.

AMF-initiated PDU Session Release with N11 Release=True
AMF-initiated PDU Session Creation Call Flow (N11 release=true) Description
Step Description
1

The AMF sends SmContextModifyRequest with release=True in 2 causes REL_DUE_TO_DUPLICATE_SESSION_ID or REL_DUE_TO_SLICE_NOT_AVAILABLE.

2, 3

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

4

The SMF sends SmContextUpdateResponse message with N1 and N2 content.

  • N1: PDU_SESSION_RELEASE_COMMAND, exclude if cause is REL_DUE_TO_DUPLICATE_SESSION_ID, skip steps 10,11,12,13

  • N2: N2_PDU_SESSION_RESOURCE_RELEASE_COMMAND. exclude if the SMF is in IDLE mode. Also, skip the steps 7, 8, and 9.

5, 6

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

7, 8, 9

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

10, 11, 12, 13

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

14, 15

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

16, 17

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

18, 19

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

20, 21

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