Are all wireless networks susceptible to interference?

There is a lot of buzz about enterprise access networks that are "completely wireless" as the increased throughput and range of next-generation 802.11n WLANs become available in IEEE standard products.

One consideration for using unlicensed radio waves exclusively for corporate LAN access is the impact of interference on network availability. Jamming is a form of wireless denial-of-service attack in which a single device transmitting at a higher power than nearby devices blocks connections to lower powered devices. If you put all of your broadcast eggs in one wifi jammer, a malicious paper jam can bring your access network to its knees.

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Fortunately, to date we haven't heard much about deliberate, unintentional jamming attacks on any particular company or hot spot. But once businesses go wireless, I wonder if that raises serious security concerns.

Inadvertent interference is common in cell-based Wi-Fi network systems. It radiates from bluetooth devices, microwave ovens, cordless phones, Wi-Fi access points in a neighboring office, and other competitors for unlicensed spectrum. You can use spectrum analyzers such as those from Cognio and its many resellers and OEMs to identify and locate such sources of interference. Basically, you then use Ankle Express to deactivate them.

But what if criminals come into play? Jamming devices exist today primarily for legitimate testing purposes. If the jammer is within FCC Part 15 performance limits - 1 watt plus 6 dBi antenna gain, or around 4 watts - a legitimate device can easily broadcast most Wi-Fi devices, which typically emit around 100 milliwatts of power Craig Mathias, Principal at Farpoint Group in Ashland, Mass.

"There are a number of jammers on the market that can completely shut down 802.11," says Mathias. "You need some kind of radio that can pinpoint where the radiation source is coming from. If the jammer is illegal [broadcast at levels above FCC limits] it can be distant and difficult to fix."