With reference to 5G networks, describe the NGAP signaling flow?
1) RRC Setup Request:
UE to 5G BTS: The UE initiates communication by sending a request to establish radio resource control.
2) RRC Setup:
5G BTS to UE: The base station acknowledges the setup request and proceeds with the RRC setup process.
3) RRC Setup Complete (NAS: Registration Request):
UE to 5G BTS: The UE confirms the RRC setup is complete and includes a request to register with the network (NAS).
4) NGAP: Initial UE Message (NAS: Registration Request):
5G BTS to AMF: The base station forwards the NAS registration request to the core network (AMF) using NGAP signaling.
5) Authentication & Security Mode:
During this step, the UE and the network perform mutual authentication and a security mode is agreed upon.
6) RRC Reconfiguration (NAS: Registration Accept):
5G BTS to UE: Post-authentication, the base station sends configuration parameters, including acceptance of the UE’s registration.
7) RRC Reconfiguration Complete:
UE to 5G BTS: The UE confirms the reconfiguration is successful.
8) NGAP: Initial Context Setup Request (NAS: Registration Accept):
5G BTS to AMF: The base station asks the core network to set up the initial context for the UE, confirming registration acceptance.
9) NGAP: Initial Context Setup Response:
AMF to 5G BTS: The AMF completes the initial context setup for the UE and sends a response to the 5G BTS.
