Oct 21 2010

Optimize Your Wireless Network

Follow these simple tips to improve wireless performance.

Wireless networks often fail to meet users' expectations, exhibiting subpar performance, either because they are not set up correctly or not optimized for maximum throughput. Wireless performance and reliability can vary hugely depending on your particular environment, and can change constantly because of factors outside of your control, making it important to use enterprise-class equipment that can monitor and adapt to changing radio frequency (RF) conditions. But some basic steps can ensure that connections to wireless access points (APs) and routers are fast and reliable.

Wireless Standards

Invest in enterprise-class Wi-Fi Certified equipment that supports 802.11n (which was ratified in October 2009) for the best performance and reliability. 802.11n operates at 2.4 gigahertz and 5.0GHz, and provides much greater throughput than the older 802.11a/b/g standards.

At 5.0GHz, 802.11n can deliver throughput of up to 450 megabits per second. Dual-band equipment, which supports 2.4GHz and 5.0GHz, costs considerably more than 2.4GHz-only devices and has less range, but it is not as prone to interference because of the clearer airspace at 5.0GHz. If your environment has equipment running at 2.4GHz, such as cordless phones and wireless mice, consider moving straight to 5.0GHz for your 802.11n deployment.

Positioning your Access Point

Complex wireless network deployments require a site survey and a design that includes repeaters to ensure wireless coverage across large spaces. For simplicity, let's take the example of a small office/home office environment that has one Wi-Fi access point (or router) running 802.11n at 2.4GHz. Position your access point as centrally as possible, off the floor, away from walls and large metal objects, such as filing cabinets.

Configuring Wireless Standards on your Access Point

Access points tend to be more reliable and offer better performance if they have to deal with only one wireless standard at a time, so configure your access point to run only 802.11n. Naturally, this requires that all your wireless devices support 802.11n. Try to enable as few standards as possible – for instance, just 802.11n, or if that's not possible, 802.11g and 802.11n.

Channel Width

After you've configured the wireless standards running on the access point, you can choose between the 20 megahertz and 40MHz channel widths. Selecting 40MHz enables 300Mbps throughput, essentially by using two 20MHz channels together (referred to as channel bonding). But not all 802.11n-certified devices support a 40Mhz channel width at 2.4GHz. Many Intel wireless adapters support only 40MHz channel widths at 5.0GHz to minimize interference with nearby devices. Also, selecting a 40MHz channel width at 2.4GHz might cause problems with other wireless equipment.

Choosing a Channel

Both the 2.4GHz and 5.0GHz bands are divided into 13 overlapping and 24 nonoverlapping channels, respectively. You need to select a wireless channel (1 to 11) for the access point to use. It's common that access points are configured by default to use channel 6 – although some scan to find the channel with the least RF noise – meaning that this channel is often used by neighboring networks, increasing the likelihood of interference.

With the help of a free program called inSSIDer, you can see what channels other Wi-Fi networks in the vicinity are using (Figure 1). Because channels in the 2.4GHz range overlap, it's best to choose channels 6, 1 or 11 (12 or 13 can be utilized in some jurisdictions, but not in the United States). It's not necessarily the case that a channel with no other wireless networks will give you the best performance, so some experimentation might be required to find the best channel. Three wireless networks should be able to operate on a channel with minimal interference.

Figure 1.  Sample InSSIDer display of channels used by nearby Wi-Fi networks 

Finally, Wi-Fi Protected Access 2 (WPA2)/Advanced Encryption Standard (AES) authentication and encryption must be configured and Wi-Fi Multimedia (WMM) must be enabled to get maximum throughput rates with 802.11n. Also, consider reducing the transmit power of the access point to the lowest level if reliability and speed are not affected, which should help reduce power consumption and lessen the chances of the access point interfering with nearby wireless networks.

Testing Throughput Using iPerf

Once the access point is configured, it's time to test the real throughput of the network. While there are several places where you can get an indication of the speed at which your network is running, such as in the Status dialog for a wireless network in Windows or the access point management console, these readings provide only an approximation.

iPerf is an open source tool for measuring throughput between two network nodes and has been compiled for Windows. iPerf consists of one executable that can be run in server or client mode. To test throughput, you will need two PCs acting as network nodes connected to the wireless network: one running iPerf in server mode and the other running iPerf in client mode. On the server node, you'll need to open firewall port 5001 inbound to the iPerf executable.

On the server node, run iPerf from the command line with the –s switch:

iPerf –s

The server should respond:
Server listening on TCP port 5001
TCP window size: 8.00 KByte (default)

On the client node, run the following iPerf command to transfer data to the server node running on IP address over a period of 2 minutes:

iPerf –c –t 120

Wait for two minutes, and the output should look something like what's shown in Figure 2:

Figure 2.  Client node throughput as measured by iPerf

In this example, considering that the server and client nodes are in different rooms and 10 meters apart, a throughput of 50.5Mbps is quite respectable.

Because of the multiple antennae and spatial streams used in 802.11n, data may take a different path when flowing back from the server to the client node. Therefore, you should perform bi-directional testing, by adding the –d (dualtest) switch to your iPerf command, to ensure throughput is acceptable in both directions. Bear in mind that this will require opening firewall port 5001 inbound on the client.

Replacement for Ethernet?

802.11n wireless networks are usually deployed in complement to a wired network; however, there may be situations where an 802.11n network could completely replace Ethernet, such as environments that are difficult to cable or where gigabit Ethernet is not a necessity. Careful analysis of current network usage would be required to determine if 802.11n could replace your wired network. 802.11n can provide the necessary security and reliability if properly planned and configured. Special attention should be given if you are running VoIP or other applications that require low latency or high throughput.