Wireless Hacks

Estimating Network Performance

Just how quickly can you squeeze data through your AP?

Many people use online tools like DSL Reports’ Speed test (http://speedtest.dslreports.com/) to estimate the performance of their Internet connection. When run from a machine directly connected to the Internet, this can give you a fairly good indication of your upload and download capacity.

This tool becomes less useful when trying to estimate the available bandwidth on other networks. For example, on a large wireless network, it is useful to measure the actual capacity of a network link regardless of the speed of the Internet connection. One useful utility for measuring performance is iperf . It is a simple, freely available tool that will run on Linux, BSD, OS X, and even Windows. You can download it online at http://dast.nlanr.net/Projects/Iperf/.

In order to measure performance, it needs to be used in pairs (one instance at either end of a link). On one end of the link to be measured, start up iperf in server mode:

rob@livia:~$ iperf -s

Note that it doesn’t matter which end is used as the “server,” as both upload and download speeds will be tested. On the other end of the link, run iperf in client mode, specifying the server to be tested:

rob@caligula:~$ iperf -c livia -r ------------------------------------------------------------ Server listening on TCP port 5001 TCP window size: 32.0 KByte (default) ------------------------------------------------------------ ------------------------------------------------------------ ...