Question: What is the correct format for the username part of the NAI in a 5G-GUTI, as specified in IETF RFC 7542?
Option 1: tmsi<5G-TMSI>.pt<AMF Pointer>.set<AMF Set Id>
Option 2: tmsi<5G-TMSI>.pt<AMF Pointer>.region<AMF Region Id>
Option 3: <AMF Pointer>.set<AMF Set Id>.region<AMF Region Id>
Option 4: tmsi<5G-TMSI>.pt<AMF Pointer>.set<AMF Set Id>.region<AMF Region Id>
Explanation: The correct format for the username part of the NAI in a 5G-GUTI, as specified in IETF RFC 7542, is tmsi<5G-TMSI>.pt<AMF Pointer>.set<AMF Set Id>.region<AMF Region Id>, where <5G-TMSI>, <AMF Pointer>, <AMF Set Id> and <AMF Region Id> are the hexadecimal strings of the 5G-TMSI, AMF Pointer, AMF Set ID and AMF Region ID respectively.