Here is performance under load graph (each virtual user performs the same set of operations/transactions):
From 5th minute (about 30 Vusers) number of transactions stops to grow (but number of users continues growing). Transaction response time increases from that moment.
I want to prove that the transaction time increases because of server limitations but not because of network bandwidth.
So I made this test from 3 machines with 90 users (30 users/PC) and with 60 users (20 users/PC). The breaking point was the same - 30 users overall. Is it sufficient technique to prove that limitation is on the server side?
It is supposed that 20 users (on each machine) does not exceed (hypothetical) channel bandwidth limit of 30 users.