Question: What is the purpose of including the Rejected NSSAI IE in a message from the network to the UE?
Option 1: To inform the UE about available S-NSSAIs for registration.
Option 2: To notify the UE of one or more S-NSSAIs that were rejected by the network during the registration process.
Option 3: To request additional NSSAI information from the UE.
Option 4: To confirm successful registration with the requested NSSAI.
Explanation: The Rejected NSSAI IE is used to inform the UE about S-NSSAIs that were included in the initial REGISTRATION REQUEST message but were not accepted by the network. This allows the UE to be aware of which S-NSSAIs are not supported or allowed, facilitating a more efficient registration process and potential re-attempt with an adjusted NSSAI request.