PDU Session Establishment — full call flow

Creating the Data Path

PDU Session Establishment creates the user-plane path from UE through gNB and UPF to the data network. The UE sends a PDU Session Establishment Request as a NAS message embedded in UL NAS Transport to the AMF. The AMF does not handle session management itself — it selects an appropriate SMF based on the DNN, S-NSSAI, and NRF service discovery results, then forwards the request. The SMF takes over session management by retrieving QoS policy from PCF, selecting and programming the UPF, and allocating an IP address.