Question: What is the primary purpose of the Nausf_UEAuthentication_deregister service operation in the 5G system?
Option 1: To update the UE's security parameters in the AUSF.
Option 2: To authenticate a UE in a different AUSF instance.
Option 3: To delete stale security parameters (KAUSF, SOR counter and UE parameter update counter) in the AUSF after successful UE re-authentication.
Option 4: To request the UDM to provide new security parameters for the UE.
Explanation: The Nausf_UEAuthentication_deregister service operation is used by the UDM to request the AUSF to clear stale security parameters after a UE has been successfully re-authenticated in a different AUSF instance. This ensures that outdated security information is removed, maintaining the integrity of the 5G system's security architecture.