How to find process which uses most bandwidth
nethogs is something similar, but shows also the process (http://nethogs.sourceforge.net/)
little clumsy solution, but
start
iftop -nNP
and after it starts, press 't' and now you need to pause by pressing 'P' (shift+p).
copy the desired 'IP:port' from 2nd column and start as super-user
netstat -tnp | grep "<paste_IP:port_here>"
and at the last field of the output you should see PID/program. hope this help.