Question: In a 3GPP system, when a Mobile Equipment (ME) attempts a full authentication for WLAN access, what is the required condition for the user name portion of the Network Access Identifier (NAI) from the USIM application perspective?
Option 1: A valid Pseudonym must be available in EF_Pseudo and used as the user name portion of the NAI.
Option 2: The IMSI (International Mobile Subscriber Identity) must be used directly as the user name portion of the NAI.
Option 3: A random username can be generated by the ME for each authentication attempt.
Option 4: The MSISDN (Mobile Station International Subscriber Directory Number) is mandatory for the NAI's user name portion.
Explanation: According to 3GPP specifications for WLAN interworking, when a Mobile Equipment (ME) initiates a full authentication for WLAN access, it must check for a valid Pseudonym in the EF_Pseudo (a file in the USIM that stores pseudonyms). If available, this pseudonym is utilized as the user name portion of the Network Access Identifier (NAI) to ensure privacy and security during the authentication process. This approach aligns with the procedures outlined for managing pseudonyms and WLAN access authentication in 3GPP system to Wireless Local Area Network (WLAN) interworking protocols.