Question: What happens if there is no full native 5G NAS security context available in the Access and Mobility Management Function (AMF) during the registration process?
Option 1: The AMF skips primary authentication and uses an existing security context.
Option 2: The AMF runs a new primary authentication and a Non-Access Stratum Security Mode Command (NAS SMC) procedure to activate a new 5G NAS security context.
Option 3: The UE is redirected to a different network for registration.
Option 4: A primary authentication run is required, and the AMF may decide to run a new primary authentication and a NAS SMC procedure after the Registration Request.
Explanation: According to the security architecture and procedures for 5G systems, if there is no full native 5G NAS security context available in the AMF during registration, a primary authentication run is required. The AMF may then decide to run a new primary authentication and a NAS SMC procedure after the Registration Request to activate a new 5G NAS security context. This ensures secure communication between the UE and the network.