The 802.11 Standard
In 1997, the Institute of Electrical and Electronics Engineers (IEEE) ratified the initial 802.11 standard which includes 1 and 2 Mbps Frequency Hopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum (DSSS), and infra-red operation in the 2.4 GHz frequency band. The first products to hit the market were based on incompatible proprietary implementations, so no guarantee of interoperability or upgradeability could be offered to customers.

802.11b
Toward the end of 1999, the IEEE ratified the 802.11a and 802.11b standards. The 802.11a standard operates in the 5 GHz unlicensed U-NII spectrum, and the 802.11b standard operates in the 2.4 GHz unlicensed ISM spectrum. Because of abundant industry expertise in building 2.4 GHz radios for existing products like cordless phones, wireless LAN products based on 802.11b quickly arrived on the market, offering Ethernet-class data rates (up to 11 Mbps) and backward compatibility with the initial 802.11 DSSS standard. 802.11b products quickly penetrated the mass market because they were the first to deliver acceptable speeds at accessible prices. Furthermore, the Wi-Fi Alliance (formerly known as the Wireless Ethernet Compatibility Alliance) began to certify 802.11b products for interoperability with one another.

Because 802.11b was the first technology to meet the requirements of enterprise, SOHO and public wireless LANs, much of the mainstream infrastructure has been built on it. In fact, 95% of wireless LAN nodes installed in the US today are 802.11b. By strength of sheer numbers, 802.11b is considered to be the industry standard in wireless LANs.

802.11a
The 802.11a standard delivers data rates of 6-54 Mpbs using Orthogonal Frequency Division Multiplexing (OFDM) in the 5 GHz frequency bands. Because of difficulties in developing 5 GHz chips, 802.11a-based products did not become available until late 2001. This has led to a low level of adoption and relatively high prices. A major problem is that 802.11a is not compatible with 802.11b. Some vendors offer dual-band access points to facilitate the coexistence of 802.11a and 802.11b networks. In the near future, dual-band 802.11 a/g will replace a/b access points.

The cost disadvantage of an 802.11a system is not limited to the price of the individual components. Because it uses the higher 5 Ghz bandwidth, 802.11a has a practical range of approximately half that of 802.11b. Lower range requires the use of more access points to cover the network geography, adding to the total cost of an 802.11a system.

802.11g
The 802.11g standard can deliver up to 54 Mbps data rates in the 2.4 GHz frequency band using OFDM. Since both 802.11g and 802.11b operate on the 2.4 GHz frequency band, they are completely interoperable. Therefore, customers can protect the investments they've made in 802.11b equipment when purchasing compatible 802.11g products. Other characteristics of 802.11g are:

• High performance that satisfies bandwidth-intensive applications and areas with many wireless users
• Backward compatibility with the installed base of 802.11b wireless LANs, reducing upgrade costs
• Lower product costs compared to an 802.11a/b solution, because only one radio is necessary with 802.11g
• Good range compared to 802.11a, which lessens deployment costs due to fewer access points in most applications
• A method of prioritizing data packets to improve quality of streaming media, such as VoIP, voice and video conferencing

Because of these features, 802.11g is quickly replacing 802.11b as the mainstream wireless LAN technology.