Question: What triggers a User Equipment (UE) to send preambles on the Physical Random Access Channel (PRACH) for a CELL UPDATE message with cause value 'cell reselection' in the context of cell re-selection delay?
Option 1: Receipt of a dedicated paging message from the new cell.
Option 2: A change in cell levels causing the UE to camp on a new cell.
Option 3: Expiration of a timer set during the initial network attachment process.
Option 4: Completion of a successful data transfer session in the previous cell.
Explanation: The correct answer is Option 2 because a change in cell levels (e.g., signal strength) prompts the UE to switch to a new cell, triggering it to initiate the cell update procedure by sending preambles on the PRACH with the specified cause value, indicating the reason for the update is cell reselection. This process reflects how UEs dynamically adapt to changing radio conditions in wireless networks, ensuring optimal connectivity.