Question: What is the procedure for a UE to determine the PLMN identity to be used for the calculation of the new KASME after a successful EPS authentication challenge when it moves from EMM-IDLE mode to EMM-CONNECTED mode?
Option 1: The UE uses the PLMN identity received as part of the broadcast system information.
Option 2: The UE uses the PLMN identity that is part of the GUTI, if available.
Option 3: The UE uses the PLMN identity of the selected PLMN until the first handover.
Option 4: The UE uses the PLMN identity that is part of the RAI, if available.
Explanation: According to the 3GPP specification, when a UE moves from EMM-IDLE mode to EMM-CONNECTED mode, it shall use the PLMN identity of the selected PLMN until the first handover. This is specified in clause 5.4.2.3 of the TS 24.301 document.