Measuring Wireless Network Performance: Data Rates vs. Signal Strength

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1 EDUCATIONAL BRIEF Measuring Wireless Network Performance: Data Rates vs. Signal Strength In January we discussed the use of Wi-Fi Signal Mapping technology as a sales tool to demonstrate signal strength of the wireless network. Now, we would like to introduce the other important measurement that all network installers should be using to validate the installation and ensure a positive customer experience. Simply Connected

2 Although signal strength is often the de facto performance benchmark, signal strength alone is not enough to determine the viability and usability of the wireless network. All Wi-Fi users have experienced occasions when a network was unusable even while showing solid signal strength something typically attributed to low data rates. For this reason, Luxul suggests that data rates (in addition to signal strength) always be tested to validate the network installation. A simple, effective and inexpensive method for testing data rates is a freeware utility called Iperf. WHAT IS IPERF? Iperf is a tool for measuring TCP and UDP throughput, jitter, and packet loss performance of IP networks. It is available for use on Windows, Macintosh, and Linux platforms. For more information, visit WHAT AND WHERE TO TEST When evaluating wireless network performance and/or comparing the performance of different wireless technologies, it is suggested to test the following: Problem Areas Test in known problem areas where signal may seem to be adequate but connectivity has been a challenge. Distance As a general rule, the further away from the access point, the lower the data rates. While at short range, there is likely little or no difference between wireless technologies, some wireless equipment maintains higher data rates at a greater distance. An installer can benefit by understanding where the network becomes unusable due to having insufficient data throughput. EQUIPMENT REQUIRED FOR THE TEST Wireless Router or Access Point to be tested Two Computers (Laptop or desktop at least one of which has wireless capability) Iperf software installed on both computers Iperf is a tool for measuring TCP and UDP throughput, jitter, and packet loss performance of IP networks. NOTE: Internet connectivity is not a requirement. Iperf only requires that the two computers and Access Point can communicate via a local area IP network. IPERF INSTALLATION Iperf is a free utility that can be downloaded for Macintosh and Linux here: or for Windows platforms here: Download the appropriate Iperf version and run the downloadable executable to save to the system. Note that the software will need to be loaded on BOTH computers being used in the test. One of the computers will be setup as the server (connected to the access point via Ethernet cable), while the other will be connected wirelessly as a client computer. Either computer can act as the server. However, it is recommended that the computer connected directly to the access point be the server, while the other computer acts as the wireless client.

3 NOTE: The following instructions are for the Windows XP version of Iperf, but may also apply to the Linux, Windows Vista and Mac versions. Server Setup Determine the IP address of the Iperf server computer: 1. Go to Start -> Control Panel -> Network and Internet Connections -> Network Connections. 2. Double click on the Local Area Connection being used. The status box should appear. 3. Select the Support tab at the top right and note the IP address listed. You will need this IP address later on. Start Iperf in server mode. 1. Open a cmd (Command Prompt) window. (Can be found in Start -> All Programs -> Accessories) 2. In the command prompt window, change to the directory where the Iperf executable was installed. (cd c:\iperf in this example) 3. To start Iperf in server mode, type in the following command: Iperf s If the server is setup correctly, the resulting output will look like the following: Image 1: Output of Iperf server setup Client Setup Verify that the wireless client computer is connected to the SSID of the access point and can ping the server s IP address. Open a cmd (command prompt) window on the client computer (can be found in Start -> All Programs -> Accessories). Change the directory to the location that Iperf was installed (i.e. cd c:\iperf). TESTING TCP THROUGHPUT After setting up Iperf, we are now ready to test throughput. The default test mode for Iperf is TCP, which simulates bi-directional IP application communication. The majority of IP applications use TCP, including the World Wide Web, , and File Transfer. The TCP command string on the client side takes the following format: Iperf c w 64kb l 64kb M 1400 i 10 t 60 (Using this command string, Iperf would report results every 10 seconds and run for 60 seconds)

4 c (IP address of server) w (only used with Windows version, specifies windows size) l (only used with Windows version, specifies packet length) M (only used with Windows version, specifies the maximum MTU size) i (interval to report throughput in seconds) t (amount of time to run test in seconds) If Iperf is operating correctly you should see something similar to this: Once the test is complete, the cumulative results are displayed on the last output line. In this example, during the 60-second interval, 138 Mbytes of data were transferred at a TCP average throughput of 19.3 Mbps per second. After completing the client test, the server will also display the cumulative results for each test. Proceed to perform multiple tests in different locations, particularly at the edge of network coverage. If comparing more than one wireless network, it is important to perform each comparative test from as close to the same location (including height) each time the test is done. Any variation can cause the test results to inaccurately reflect the true performance. If the testing is done in an environment where multiple wireless networks are present, then it is advisable to perform several tests from each location during the course of a day or multiple days. This level of testing will take longer but should result in a more reliable result. Image 2: Example of TCP throughput data using Iperf

5 TESTING UDP THROUGHPUT UDP test mode simulates real-time streaming applications such as VOIP and Video Streaming. To test UDP throughput, the server side must be restarted with the following command: Iperf s u NOTE: To stop Iperf at anytime enter ctrl c Example client UDP command string: Iperf c w 64kb l 64kb M 1400 i 10 t 60 u b 35m u signifies the UDP test and the b signifies the UDP bandwidth. (35m = 35Mbits per sec, default is 1Mbit per sec.) The output should look something like the following: Image 3: Example of UDP throughput data using Iperf In this example, during the 60-second interval, 159Mbytes of data were transferred at a UDP average throughput of 22.2 Mbps per second. The average jitter was ms. The packet loss percentage was (0.085%) with 145 of packets lost. The greater the UDP data rate, the greater the likelihood that your packet loss percentage will increase. While wireless networking can be a challenge, there are steps that can be taken to ensure optimal performance and user satisfaction. Testing both signal strength and data throughput will help identify potential holes in network coverage and allow network installers to take the appropriate steps to ensure an optimal wireless network experience.