Network-initiated Idle to Active Transition Call Flow
The following figure depicts the network-initiated idle to active transition call flow.

Step | Description |
---|---|
1 |
The UPF sends PFCP Session Report request to the SMF.
|
2 | The SMF sends the PFCP Session Report response. |
3 |
The SMF sends N1N2MessageTransfer to AMF with the following attributes:
|
4 |
The SMF receives N1N2 Transfer Response with the following status codes:
|
5 | The AMF sends the N1N2 Transfer failure response. If the UE is not reachable, proceed to Step 7. |
6 |
Then, the AMF requests the SMF by sending POST request with the following information:
|
7 |
The SMF initiates PFCP Session Modification procedure towards UPF with downlink FAR updated with the following options:
|
8 | Upon receipt of successful response from UPF node, the SMF sets the upCnxState attribute to ACTIVATED for the PDU session. |
9 | The SMF then initiates 200 OK response including the upCnxState attribute set to ACTIVATED towards AMF (only if Step 6 is completed and response is received from Step 8). |