Question: In the context of 5G performance measurements, how is the Downlink (DL) delay calculated on the F1-U interface for a GTP packet?
Option 1: Time when receiving a GTP packet delivery status message from the gNB-DU at the egress GTP termination, minus time when sending the same packet to gNB-DU at the GTP ingress termination, minus feedback delay time in gNB-DU, then divided by two.
Option 2: Time when sending the GTP packet to gNB-DU at the GTP ingress termination, plus time when receiving a GTP packet delivery status message from the gNB-DU at the egress GTP termination, plus feedback delay time in gNB-DU.
Option 3: Average of the time when receiving a GTP packet delivery status message and the time when sending the same packet to gNB-DU, without considering feedback delay time in gNB-DU.
Option 4: Maximum of the time when receiving a GTP packet delivery status message from the gNB-DU at the egress GTP termination and the time when sending the same packet to gNB-DU at the GTP ingress termination.
Explanation: The correct calculation for DL delay on F1-U involves subtracting the send time from the receive time, adjusting for the feedback delay in gNB-DU, and then dividing by two to account for the round-trip nature of the measurement, accurately assessing performance within the user plane connection quality in 5GS.