Implementing 802.11g: Stop dropped connections

What happens when you try implementing wireless 802.11g in a place with no open spaces (picture slim hallways to separate closed-in rooms, about 50 per floor)? You may have noticed -- or your clients may have complained about -- a disconnection and a reconnection when switching APs. So you've used a rule of thumb applying 1 AP per 3000 square feet and your clients still aren't able to roam seamlessly? Here's why and what you can do about it:

802.11 stations automatically try to associate with the "best" AP with a given SSID. "Best" can be based on many factors, including signal strength, error rate, and link speed. When a station associated with one AP decides that another AP might be better, it disassociates from the old AP and associates to the new AP. This roaming process of course takes time.

If your APs are in the same subnet with no security enabled, roaming may be barely noticeable. If your APs require WPA or WPA2-Perso

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nal, PreShared Key authentication will add many milliseconds of latency. If your APs require WPA or WPA2-Enterprise, the full-blown 802.1X authentication can add seconds of latency, which users perceive as broken connections. If your APs are in different subnets, every TCP and UDP session must be restarted: the user's worst case scenario.

Depending upon your network, you may have several options to speed roaming: Finally, if your clients are actually experiencing dead spots and loss of signal, speeding AP handoff won't really fix your problem. You could try to back-fill those dead spots, but that can be costly or even impossible in some environments (like hospitals). In that case, consider using a mobility client to provide application session persistence (e.g., Columbitech, Ecutel, IBM, ipUnplugged, Motorola, NetMotion). To learn more, read this SearchMobileComputing tip.

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