Question: In UTRA TDD, what event marks the end of the interruption time when a UE initiates an RRC CELL UPDATE message?
Option 1: The last TTI (Transmission Time Interval) the UE monitors the Dedicated Channel (DCH) on the serving cell.
Option 2: The instant the UE completes sending preambles on the PRACH (Physical Random Access Channel).
Option 3: The time instant the UE starts to transmit the RRC CELL UPDATE message to the UTRAN on the RACH (Random Access Channel).
Option 4: The first TTI the UE receives an acknowledgement for the RRC CELL UPDATE message from the UTRAN.
Explanation: According to the definition specific to UTRA TDD, the interruption time concludes at the precise moment when the User Equipment (UE) initiates transmission of the RRC CELL UPDATE message on the Random Access Channel (RACH), marking the transition from monitoring to active communication for cell update purposes. This highlights a critical point in radio resource management where the UE shifts from passive reception to initiating a handshake for updating its cell association, impacting network signaling and resource allocation.