Question: During a Tracking Area Update (TAU) procedure in E-UTRAN, how is the TAU Request message protected by the UE using the current EPS security context?
Option 1: Both integrity and confidentiality protection are applied to the entire message.
Option 2: Only integrity protection is applied to the message, without confidentiality protection.
Option 3: Neither integrity nor confidentiality protection is applied until a NAS SMC is completed.
Option 4: The protection depends on the presence of pending downlink UP data or signaling.
Explanation: According to the specified security procedures for TAU in E-UTRAN, the UE must integrity-protect the TAU Request message using the current EPS security context algorithms, but it does not apply confidentiality protection. This ensures the message's authenticity and integrity without encrypting its content.