Question: In EAP-AKA' authentication, how is the username part of the Fast Re-authentication NAI modified according to 3GPP specifications?
Option 1: The username part is appended with the string '3GPP'.
Option 2: The username part remains unchanged.
Option 3: The username part is prepended with a single digit '8'.
Option 4: The username part is suffixed with the MCC and MNC of the HPLMN.
Explanation: According to specifications for EAP AKA', to form the Fast Re-authentication NAI, the username part must be prepended with a single digit '8', distinguishing it from other protocols like EAP-AKA and ensuring compatibility during telecom network authentication.