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WLAN Design: Page 5 of 6

Jesse Lindeman is the lab manager at the Center for Emerging Network Technologies at Syracuse University. Write to him at [email protected].

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802.11b: 2.4 GHz; supports speeds up to 11 Mbps and provides three nonoverlapping channels.

802.11a: 5-GHz UNII (Unlicensed National Information Infrastructure) band; supports speeds up to 54 Mbps. Although capable of only two-thirds the range of 11b, 11a offers up to 12 nonoverlapping channels.

802.11g: 2.4 GHz and backward-compatible with 11b. Supports speeds up to 54 Mbps, but with a greater range than 11a (75 percent of 11b's). Operates with the same three nonoverlapping channels and experiences the same RF (radio frequency) interference as 11b. Throughput suffers when both 11b and 11g clients are present.

Hidden Node: Two clients associated with the same access point can't hear each other to determine when the medium is free for transmission. To resolve the problem, reduce the power output of the AP so the clients can hear or enable RTC/CTS (request to send/clear to send), a high-overhead mechanism in APs that confirms the medium is clear before any data is sent.

Interference: Competing RF (radio frequency) signals in the same band as your WLAN equipment--coming from other WLAN infrastructure or non-networking devices, such as microwaves and cordless telephones.