But there are tradeoffs. The biggest is as radio waves increase in frequency, range decreases. This is part of the reason why AM radio stations, which operate at a lower frequency, have a greater transmission distance than FM stations. With both 11a and 11b the signal strength drops off the further the user is from the nearest AP. As the signal strength drops, so does the data transmission rate. The higher frequency 11a signal drops off much quicker than the 11b, giving it a sharply limited range. This means that it requires more APs than 11b to cover the same area.
The exact distance either can effectively cover depends on where they are deployed. Items such as walls, filing cabinets and glass are obvious barriers. But water also does an excellent job of absorbing the signal and can cause unanticipated signal losses. No, it’s not likely users will using their laptops underwater, but the human body is largely composed of water. As a result, colleagues standing around one’s desk can drastically cut network performance. When using access points for outside areas of a campus, trees, which also contain huge amounts of water, will also create blind spots.
The Middle Road
802.11g is designed to address the shortcomings of both the earlier standards. To start with, it has the same high 54Mbps data rate of 11a, but does this over the wider range provided by 11b. It operates on the 2.4GHz frequency and is fully backwards compatible with 11b. This means that if someone has an 11g card on their laptop, they can authenticate onto APs that are using either the 11b or 11g protocols.
This would seem ideal but, as mentioned earlier, actual results may vary.
An 11g device logged onto an 11b AP will shift down to the 11b data rate, so there is no advantage to 11g unless both are operating with 11g. But it gets worse. For an AP to operate at 11g rates, every device logged onto it must be operating in 11g. If there is even one device using 11b all the others will automatically revert to the lower protocol. So, if you have 11g in your office, and one person pulls out his 11b PDA to check his email, everyone on that network segment suddenly experiences a performance drop.
Making The Choice
So, which way should you go: a, b or g? 11g is slightly more expensive than 11b, but offers a speed advantage.
“11g will be more useful to some degree in homes and in businesses where you can control the environment and make sure it is all 11g,” says Gartner Vice President Ken Dulaney. “But unless you are regularly transferring large files inside the house it is not that useful, since what is going outside the house is a DSL or cable connection operating at a couple hundred kilobits (Kbps).”
For enterprise settings, Dulaney advises going with 11a since has the high data rate and is less susceptible to interference. Also, within a crowded office setting the shorter transmission distance and greater number of channels can both be advantages. When you have a large number of users in a small space, you want to be able to put more access points in the area without their signals overlapping. The downside is that employees won’t be able to take their laptops out on the road and log in at public hot spots.
So, if you can’t make up your mind which to use, go with all three. Most vendors offer wireless devices that operate on all three standards. They do cost about 30% more than ones operating on a single protocol, but they offer the highest degree of flexibility.
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