Question: What is the required format of the NAI for SUPI as specified in IETF RFC 7542?
Option 1: username#realm
Option 2: username-realm
Option 3: realm/username
Option 4: username@realm
Explanation: The correct format of the NAI for SUPI is specified in clause 2.2 of IETF RFC 7542 as "username@realm". This format is used to identify a user and their associated realm, which may include MCC, MNC, and NID of the SNPN in certain scenarios.