Question: What does the network use to determine whether the mobile identity included in the Mobile identity IE is a native P-TMSI or a mapped P-TMSI when it receives an ATTACH REQUEST message containing the P-TMSI type IE?
Option 1: The most significant bit of the LAC
Option 2: The IMSI and CKSN values
Option 3: The old RAI value
Option 4: The P-TMSI type IE
Explanation: According to the specification, when the network receives an ATTACH REQUEST message containing the P-TMSI type IE and does not follow the use of the most significant bit of the LAC as specified in 3GPP TS 23.003, it uses the P-TMSI type IE to determine whether the mobile identity included in the Mobile identity IE is a native P-TMSI or a mapped P-TMSI.