The Wi-Fi Professor: Perry Correll

Free Wi-Fi Tools: iPerf for Wi-Fi Performance Measurements

Continuing with the discussions of free Wi-Fi tools, we come to iPerf. Important note, iPerf is not specific to wireless and can be used in any IP environment; however increased interest in its use in Wi-Fi is the result of more administrators deploying 802.11n networks.

iPerf is an easy to use and very popular tool designed to measure communication channel characteristics, I strongly recommend every IT professional have a copy and be comfortable with its use. iPerf operates in a client server manner, generating traffic between two devices and measuring key network criteria. It provides feedback in easy to understand tables and graphs, showing throughput, packet loss, jitter etc. between the client and server. Using this information you are able to tweak (tune) TCP and UDP data settings to optimize connection. iPerf can be run from a command line or a GUI interface (called jPerf).

As mentioned, a primary purpose of iPerf is to allow you to ‘tune’ connections. I am not going to spend time going into depth on the variables of TCP or UDP but there are some basics worth mentioning.

When tweaking a TCP connection the place to start is the TCP window size, the window size determines the amount of traffic a client can transit at any one time.  If too much traffic is sent buffers can be exceeded, too little and the connection is not optimized. iPerf can be used to test transfer rates  across a link while varying the window size. Based on this testing the optimum window size can be determined and the network optimized. A good tutorial for more information on window size is available at

UDP traffic does not offer the guarantees of TCP, error or flow control. It is a connectionless protocol and often used for streaming information such as voice or data with no concern (at this layer) for loss. When tweaking a UDP connection the adjustment here is the packet size. UDP testing is useful in determining bandwidth, jitter and packet loss.

As I mentioned iPerf can be used in any IP environment, however of late there is increased interest in it for testing Wi-Fi links. As most are aware, RSSI values identified by many Wi-Fi clients only estimate what physical layer data rates you could expect. They typically do not take into consideration SNR (Signal to Noise Ratio), packet loss, management overhead and other conditions that influence the rating algorithms and define your actual layer 3 throughput numbers. As more and more users are moving to 11n for the increased bandwidth it offers, many want to see what the actual improvements are over legacy 11a/g throughputs.

The below graphic (using the GUI interface) is an example of a Wi-Fi throughput test between an iPerf client (wireless laptop) and an iPerf server (Xirrus Array), as you can see the throughput averaged in the 180Mbps range.  This is actual TCP throughput, not link rate.


To simplify testing and as a value add for their customers, many vendors (including Xirrus) have integrated iPerf in their products.

Getting iPerf:

Iperf is copyrighted by the University of Illinois, except for the gnu_getopt.c, gnu_getopt_long.c, gnu_getopt.h files, and inet_aton.c, which are under the GNU General Public License.

Iperf 2.0.2 installer for Windows – Provided by Ted Fines ( at Macalester College, St. Paul, MN.

To download iPerf, click here: kperf_setup.exe

iPerf tutorials:

Thanks for visiting, in a following post I will discuss some of the other ‘dials’ you can tweak and test with iPerf

The Prof


13 Comments so far
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Thanks for the info! I did a little research and found Jperf linked from . It was just what the doctor ordered for wifi (wireless) throughput! Thanks again.

Comment by Stephen

Oops… Jperf was linked from this page at

Comment by Stephen

I’d also like to recommend a free tool called WaveDeploy, the free version of which maps TCP performance to a physical location. This tool can be very valuable to identifying locations that have poor performance due to nearby interference sources, poor AP placement, etc. The Pro and Expert versions provide measurements across a wide variety of platforms including Windows, Linux, Mac OS, iPhone, etc. and provisions for testing at scale.

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[…] Re: There is a problem with your connection Never heard of it, but you might have packet loss since its wifi. Test that if you have some app that controls it if not check this out […]

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