Question: What is a key characteristic of the username part in an Alternative Network Access Identifier (NAI) as per 3GPP specifications for telecom networks?
Option 1: It must be derived from the International Mobile Subscriber Identity (IMSI).
Option 2: It shall not be derived from the IMSI and must be a non-null string.
Option 3: It can be any string but the REALM part must vary accordingly.
Option 4: It is always a null string to ensure anonymity.
Explanation: In telecom networks, especially within the context of 3GPP specifications, the Alternative NAI's username part is designed to maintain user privacy and security. By not deriving it from the IMSI (a unique identifier for mobile subscribers), the system enhances anonymity. Additionally, requiring a non-null string ensures that the username has meaningful content, preventing potential misuses or errors associated with empty fields. This setup is crucial for secure authentication processes in wireless communications.