Total delay for all packets in 5G calculation

Hi Experts.

As per TS 28.552

Average delay DL on F1-U
This measurement is obtained as: the time when receiving a GTP packet delivery status message from the gNBDU 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, obtained result is divided by two. Separate counters are optionally maintained for each mapped 5QI (or QCI for option 3) and for each S-NSSAI.


Calculate the total delay for all packets:
Total Delay = (Time of receiving packet at egress GTP termination - Time of sending packet to GTP ingress termination - Feedback delay time)

Divide the total delay by the number of packets and divide by 2

My question is:

Why we subtract Feedback delay time? And why divide by 2?