Question: In a 5GS network, how does a UE (User Equipment) determine if Access Identity 2 is valid when the USIM (Universal Subscriber Identity Module) file EFUAC_AIC does not indicate configuration for Access Identity 2?
Option 1: By checking the MCS (Mobile Country Code) indicator bit in the 5GS network feature support IE of the REGISTRATION ACCEPT message.
Option 2: Through direct query to the 5G network's SIB1 (System Information Block 1) for Access Identity 2 validation.
Option 3: By analyzing the barring control information broadcasted in SIB1 for a match with its SUPI (Subscriber Permanent Identifier).
Option 4: The UE cannot determine validity without EFUAC_AIC indication and relies on default settings.
Explanation: According to the specifications, when the USIM file EFUAC_AIC does not indicate configuration for Access Identity 2, the UE uses the MCS indicator bit of the 5GS network feature support IE in the REGISTRATION ACCEPT message to determine if Access Identity 2 is valid. This method ensures the UE can assess the validity based on network-provided information when local USIM configurations are incomplete.