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More spectrum talk

Feb 20, 20062 mins
Cellular NetworksNetwork Security

* The 2.4-GHz frequency’s Achilles heel

As you likely know, 802.11b/g networks share the unlicensed 2.4-GHz spectrum with Bluetooth networks and a plethora of consumer electronic devices. Among these are some cordless phones, microwave ovens, and baby monitors.

Aside from the band simply being crowded with increasing numbers of devices, the limit of three non-overlapping channels in this band makes it more difficult to manage interference than in the 5-GHz band, where more channels are available. As you build overlapping Wi-Fi “cell” sites next to one another out of Wi-Fi access points to blanket an area with Wi-Fi signal coverage, you simply have to repeat the use of a given channel more often when there are fewer of them to go around.

When building a network of a significant size using just the 2.4-GHz band, you might consider the use of a spectrum analyzer from a company such as Cognio (or its latest reseller, AirMagnet). These analyzers will not only discover interference across the entire spectrum band, but will also alert you to the type of device that’s “in the way” so you can find it and do something about it. The tool identifies the device based on its modulation method.

If it’s a microwave oven that’s the culprit, for instance, you might opt to get a new one that has better sealing on its door to keep radiation inside. That’s what Sacred Heart Medical Center in Spokane, Wash., did using AirMagnet’s Spectrum Analyzer. It discovered that the microwave in the break room “would totally take out channel six” in its 802.11g/b network when in use, causing intermittent connectivity problems in the pediatric ward across the hall, says Jed Orton, network technician.

By contrast, the 5-GHz spectrum supports up to 24 channels, depending on what country you’re in. If you use both spectra (some 11g or b networks combined with some 11a networks), you could get the design flexibility of 27 channels.