Question: What is the primary event that triggers the start of the cell re-selection delay timer in a UTRA FDD UE supporting E-UTRA FDD?
Option 1: A change in cell levels (e.g., serving cell's signal strength decreases or a neighboring cell's signal strength increases)
Option 2: Receipt of a Tracking Area Update command from the network
Option 3: Successful transmission of an RRC CONNECTION REQUEST message on the current cell
Option 4: Detection of a new cell with identical signal strength to the currently serving cell
Explanation: The cell re-selection delay starts upon a change in cell levels, which could be due to movement away from the current cell or towards a stronger neighboring cell. This event triggers the timer that ends when the UE camps on a new cell and initiates procedures for updating its tracking area on the new cell, highlighting the importance of signal strength monitoring in facilitating seamless handovers within telecom networks.