Question: What is the purpose of including the Alternative NSSAI IE in the NAS message by the network?
Option 1: To request the UE to perform a periodic registration update.
Option 2: To provide the UE with information about available PLMNs.
Option 3: To indicate to the UE that it needs to re-establish a PDU session.
Option 4: To provide mapping information between the S-NSSAI to be replaced and the alternative S-NSSAI to the UE.
Explanation: The Alternative NSSAI IE is used by the network to inform the UE about the mapping between the old and new S-NSSAIs, allowing the UE to update its internal state accordingly. This information is essential for maintaining seamless communication services during network updates or reconfigurations.