Question: In a UTRA FDD network, what marks the end of the cell re-selection delay for a User Equipment (UE) supporting HS-DSCH 2nd DRX operation in Release 11 or later?
Option 1: The moment the UE receives an acknowledgement from the UTRAN for a previous CELL UPDATE message.
Option 2: The instant the UE decides to switch to a new cell based on measured signal strengths.
Option 3: The time when the UE completes the transmission of the RRC CELL UPDATE message on the uplink shared channel (UL-SCH).
Option 4: The moment the UE starts sending preambles on the Physical Random Access Channel (PRACH) for transmitting an RRC CELL UPDATE message to the UTRAN.
Explanation: According to the definition, the cell re-selection delay ends when the UE initiates the process of informing the UTRAN about the cell change by starting to send preambles on the PRACH, which is specifically for sending an RRC CELL UPDATE message. This marks the transition from the decision to re-select a cell to actively communicating this change to the network.