Question: In the context of 5G performance measurements on I-UPF (Interworking User Plane Function), how is the round-trip N9 delay measured for the 'Distribution of round-trip N9 delay on I-UPF' measurement?
Option 1: By calculating the time difference between sending a GTP echo request to the PSA UPF and receiving an ICMP response at the I-UPF's ingress.
Option 2: Through direct probing of the network infrastructure by the I-UPF, without involving the PSA UPF.
Option 3: By subtracting the time of sending a GTP echo request message to the PSA UPF from the time of receiving the associated GTP echo reply message at the I-UPF's ingress GTP termination.
Option 4: Based on periodic reports from the User Equipment (UE) regarding its perceived network latency.
Explanation: This is correct because the method involves calculating the difference between the time a GTP echo request is sent to the PSA UPF and the time the corresponding GTP echo reply is received, accurately reflecting how round-trip delay over the N9 interface is measured for performance assessment in 5G networks, focusing on the interaction between I-UPF and PSA UPF.