Differences between 802.11b/g and 802.11a and 802.11n
Everyone has a wireless network today but when you dig into the details you quickly find that there are four competing wireless standards. What are these standards and what, exactly, are the differences between them?
The oldest wireless standard that is still in widespread use is 802.11b. Access points for 802.11b use the 2.4 Ghz wireless spectrum and are limited to no more than 11 Mb/s throughput. Fourteen overlapping 20 Mhz channels were allocated, of which 11 can be used in the US. Because of the overlapping nature of the wireless channels, you can only use 3 of them (1, 6, and 11) without causing interference with each other. This standard received wide adoption but would be a historical footnote except for the fact that 802.11g came out and promised full backwards compatibility for the earlier "b" standard.
The 802.11g standard is probably the most widely installed wireless standard today. Like the "b" standard, "g" uses 2.4 Ghz for all of its communications and, because of backwards compatibility, uses the same channel scheme that "b" used, with all the same limitations. If it has all the same limitations, why create the new standard? The most obvious reason is pure performance. Where "b" was limited to 11 Mb, "g" could go all the way up to 54 Mb!
The 802.11a standard, by comparison, is a completely different animal. Instead of using 2.4 Ghz for data transmission, 802.11a uses 5 Ghz. Also, like "g", "a" can send data at 54 Mb/s. Because the transmission frequency is not the same as "b" or "g", there is no backwards compatibility or interoperability at all between the standards. If there's no interoperability and no speed boost, why would anyone choose to install "a" instead of"g"? In a word, channels. Where 802.11b/g only had 3 non-overlapping channels, 802.11a has 8 channels for indoor use, none of which overlap. This allows for a lot more flexibility when doing an installation in a complex environment. It is also important to note that the higher frequency (5 Ghz vs. 2.4 Ghz) also tends to mean that 802.11a has a shorter effective range.
The final wireless standard to discuss is 802.11n. This standard is far and away the youngest of the standards currently being deployed. Depending on how it is installed, "n" can use 2.4 Ghz or 5 Ghz or both for data transmission. Most "n" devices promise backwards compatibility with "g" devices but if you use it, all devices will be limited to the speed of the slowest devices on the network. The main driver for installing 802.11n is speed... in a pure "n" environment with no backwards compatibility slowing it down, 802.11n can realize speeds up to 300 Mb/s!