What is Iperf?

While tools to measure network performance, such as ttcp,
exist, most are very old and have confusing options. Iperf
was developed as a modern alternative for measuring TCP 
and UDP bandwidth performance.

Iperf is a tool to measure maximum TCP bandwidth, allowing
the tuning of various parameters and UDP characteristics.
Iperf reports bandwidth, delay jitter, datagram loss. 

WWW: http://iperf.sourceforge.net/