When I am called in to investigate application performance issues, I try to determine if the issue is related to delays or errors.
A delay is pretty straightforward; there is a noticeable delay between the request and reply.
An error is a bit trickier but can be summed up as an application or network error delaying or corrupting the packets.
In this video I cover some Wireshark tips and tricks to filter the traffic and why iperf had an initial delay of 22 seconds.