Question: In a 5G NR network, during an inter-frequency handover from an NR Frequency Range 1 (FR1) cell to an NR Frequency Range 2 (FR2) cell, what is the key factor determining the time (`Dhandover`) within which a User Equipment (UE) must start transmitting on the new uplink PRACH channel after receiving a handover RRC message?
Option 1: The UE's current downlink signal strength in the source FR1 cell.
Option 2: The applicable RRC procedure delay plus the interruption time as defined in relevant 3GPP specifications.
Option 3: The number of active bearers and their respective QoS requirements at the time of handover.
Option 4: The target FR2 cell's load and available resource blocks for the UE.
Explanation: This is because `Dhandover`, the time within which the UE must be ready to start transmission on the new uplink PRACH channel, is determined by the sum of the applicable RRC procedure delay and the interruption time. This ensures a standardized and predictable handover process across different network implementations, focusing on procedural and interruptive delays inherent to the handover process.