Question: In a TDD (Time Division Duplex) system for UEs (User Equipment) supporting HSUPA (High-Speed Uplink Packet Access), what marks the end point for measuring the E-TFC (Enhanced Transport Format Combination) selection delay when initiated by a +1 TPC_Cmd (Transmit Power Control Command)?
Option 1: The moment the UE's transmit power reaches its maximum allowed value.
Option 2: The instant the SS (Serving Cell or Base Station) acknowledges receipt of the UE's updated E-TFCI (E-TFC Indicator).
Option 3: When the UE successfully transmits a packet using the new TFC (Transport Format Combination).
Option 4: The moment the UE's E-TFCI becomes 0 after receiving TPC_Cmd=+1 from the SS.
Explanation: This answer directly aligns with the definition provided in the context, highlighting the precise endpoint for measuring the E-TFC selection delay. This demonstrates a nuanced understanding of how timing is critical in adjusting transmission formats to maintain efficient and reliable communication between the UE and the network.