Initial Registration — full call flow

The Most Complex 5G Procedure

Initial registration involves seven or more network functions and twelve or more signaling messages, all completing within roughly 100 milliseconds on a well-configured network. The UE first establishes an RRC connection with the gNB, then sends a Registration Request NAS message carried inside an NGAP Initial UE Message to the AMF. The AMF selects the AUSF for authentication, runs the 5G-AKA procedure, activates NAS security, registers with UDM, and optionally establishes an initial PDU session before sending Registration Accept.