N4 Session Establishment Call Flow

N4 Session Establishment is used to create the initial N4 session context for a PDU session at the UPF. SMF assigns a new N4 session ID and provides it to the UPF. The N4 session ID is stored by both entities and used to identify the N4 session context during their interaction. SMF also stores the relation between the N4 session ID and PDU session for a UE.

StepDescription
1SMF receives the trigger to establish a new PDU session or change the UPF for an established PDU session.
2SMF sends an N4 session establishment request message to the UPF that contains the structured control information which defines how the UPF needs to behave.
3UPF responds with an N4 session establishment response message containing any information that the UPF has to provide to the SMF in response to the control information received.
4SMF interacts with the network function which triggered this procedure. For example, AMF or PCF.