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.

Step | Description | ||
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1 |
This procedure can be triggered by PCF, CHF, UDM, UPF or CLI (clear subscriber) to initiate the release of a PDU session. |
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2, 3 |
The SMF sends N4SessionReleaseRequest to the UPF. The UPF sends response for the same.
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4 |
The SMF sends N1N2MessageTransfer message with N11, N1 and N2 content.
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5 |
The AMF responds back to the SMF with the cause included in the N1N2MessageTransferRsp message.
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6, 7 |
The AMF exchanges the message with RAN. The RAN forwards it to the UE. |
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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. |
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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. |
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15, 16 |
The SMF sends delete charging request to the CHF. The CHF responds back to the SMF with delete response. |
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17, 18 |
The SMF sends SmContextStausNotify to the AMF. The AMF responds back with the SmContextStausNotifyResponse message. |
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19, 20 |
The SMF sends delete request to the PCF. The PCF responds back to the SMF with delete response. |
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21, 22 |
The SMF sends UDM deregistration request. The UDM responds back to the SMF with deregistration response. |