So far, wireless networks have had a free ride. They are fairly exotic, and wireless cards still aren't common (though they're selling quickly and, as a result, becoming less expensive), so wireless networks tend to have relatively few users, and the networks themselves are physically relatively far apart. What happens when they're stressed? What would a wireless network be like if it had, say, 1,000 users (which can easily be supported by a well-designed wired network)? What would it be like in a large office building, where you might have half a dozen companies, each with its own network, in the space of two or three floors?
We don't really have the answers to these questions yet. As wireless becomes more common, we'll be forced to answer them. It is clear, though, that there are resource constraints. Current technologies will suffer from overcrowding within the unlicensed 2.4-GHz band. 802.11a and other technologies will move to the 5-GHz band, but crowding will eventually become an issue there, too. Meanwhile, commercial users are fighting for additional frequency space, and it's not likely that governments will allocate more spectrum to unlicensed users.
There are a few ways out of this problem. Improved encoding techniques will help; the use of directional antennas may make it possible for more devices to coexist within a limited space. Directional antennas aren't without cost: the more effective a directional antenna is, the harder it is to aim. It's all very nice to imagine sitting at a picnic table in front of your company's office with your portable antenna aimed at the access point on the roof; but what if somebody else sits down and knocks over the antenna? How much of a pain will it be to reorient it?
Other solutions have already been mentioned in the discussion of continuing standards work. We'll certainly see cards that can switch between high-power and low-power transmission, possibly even changing channels on the fly as power requirements change.
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