http://wifi.solarissky.net/protocols.html
802.11b (11b)
Frequency Used: 2.4 GHz ? This is a fairly crowded span of spectrum. Bluetooth (short-distance wireless data transfer) and 2.4 GHz phones are especially good at disrupting an 11b signal. Microwaves can also have an effect. But the signal can go for a longer distance, and the main concern really are the 2.4 GHz phones.
Speed: 11 Mbps ? This is still faster than most home broadband Internet connections, which means surfing the Internet is not a problem. But when transferring data from one computer to another, it?s considerably slower than normal wired Ethernet or 54a, which can be a problem when streaming audio or video from one computer to another.
Comments: Despite the speed issues, 11b was the first protocol to come out, and it?s a LOT cheaper than 54a now. This is also the most common technology, which means that your 11b card can be used to connect to almost any public AP (hotspot) or another wireless network, because chances are they?ll be using 11b as well. 11b equipment is definitely the cheapest, and when it comes to adding fancier hardware (a wireless bridge or a wireless print server, for example), you will find more products that support 11b than 54a.
802.11b+ (11b+)
Speed: 22 Mbps ? Manufacturers such as D-Link and U.S. Robotics produce hardware that runs in the 2.4 GHz spectrum and are backwards-compatible with plain-old 802.11b products. However, both companies have implemented some extra technology that makes their specific equipment run at twice the speed of normal 802.11b.
Comments: Incompatibility is not necessarily a bad thing, but these are proprietary extensions to the 802.11b standard. To get the full 22 Mbps out of any 11b+ equipment, all of your networking products must be from D-Link or U.S. Robotics. 11b+ products from these companies are interoperable, but if you mix in any standard 11b equipment, that link in your network will only run at 11 Mbps. With 54g products coming out, the non-standard 11b+ technology seems unnecessary. I'd wait for those if you need the extra speed.
802.11a (54a)
Frequency Used: 5.8 GHz ? Fairly unused, but the signal travels at a shorter distance, so it's not as strong through walls.
Speed: 54 Mbps ? Fast enough for streaming audio and video from one computer to another (generally). However, most broadband Internet connections are much slower than this, so the speed is only useful for inter-network transfers. For Internet browsing, 54 MBps is more than enough speed.
Comments: Since this technology operates in a different radio band than 11b or 54g, it?s not compatible with 11b or 54g, and this has severely limited deployment and popularity of 54a. However, many equipment makers make dual chipset 54a/11b access points and cards, and this means that users with either type of card can connect to the access point. These access points are called dual-band APs.
802.11g (54g)
Frequency Used: 2.4 GHz ? Same frequency as with 11b, so all the same rules apply.
Speed: 54 Mbps ? This is the big difference. Through some electrical engineering magic I don?t understand, 54g runs at 54 MBps, which is the same speed as 54a. The kicker? 54g, because it uses the same frequency as 11b, is backwards compatible with 11b. And that?s amazing because 11b is already so common that companies (and home users) can replace equipment gradually instead of having to tear out an entire wireless infrastructure to replace it (which would be the case going from 11b to 54a).
Comments: The problem with this protocol right now is that the 54g standard has not been officially ratified by the powers-that-be. There are draft standards out there, and some companies have been releasing products based on that draft standard. The problem with that is if the standard changes a lot by the time it?s ratified ? users may very possibly be stuck with hardware that is incompatible with the final standard. However, once 54g comes out, users can upgrade slowly to 54g ? for example, users can upgrade their access point and wireless cards, but leave their print server on the 11b protocol. It won't require as much change, and that's good for users.