802.11g

To keep up with the 54-Mbps speed claims of 802.11a, the 802.11g protocol was ratified in 2003. This protocol took the OFDM modulation technique of 802.11a and applied it to the 2.4 GHz spectrum of 802.11b. Because it operated in 2.4 GHz, it was possible to remain backwards-compatible with 802.11b equipment. 802.11g radios support both OFDM and DSSS modulation techniques. Therefore, an 802.11g device would, in theory, be compatible with an original 1 or 2 Mbps 802.11 DSSS device from 1997.
Keep in mind that a typical residential or small business hotspot has a DSL or similar connection behind it providing the bandwidth to the Access Point.These broadband connections typically provide speeds in the 1.5 to 3 Mbps range. Obviously, the bottleneck in a Wi-Fi deployment is usually the DSL (or even T1) pipe.Therefore, the advantages of higher speed wireless connections (such as 802.11g) are often limited because of the Internet connection.The only exception would be if there is a large number of data transfers between wireless clients and PCs on the local area network (or between two wireless PCs). In those cases (such as gaming or local file transfers), users will notice a significant speed increase when using 802.11g,  compared to slower wireless protocols, such as 802.11b. In many large-scale community wireless networks, a system of repeaters will be used to enhance coverage in dead spots. Because each repeater (such as WDS) reduces the bandwidth by half, using 802.11g (and 54 Mbps) is often desirable.The logic here is that you can halve 54 Mbps more times then you can halve 11 Mbps, and yet still wind up with a useable, decent bandwidth speed for the client.
The pros and cons of 802.11g are as follows:

• Upside: Relatively fast speed; compatible with 802.11b
• Downside: Interference from other 2.4 GHz devices; only three non-overlapping channels

802.11b

For many years, 802.11b was widely regarded as the most popular form of Wi-Fi. It utilizes frequencies in the 2.4 GHz range (2.400–2.485GHz) and has 11 channels. However, only three of these channels are truly non-overlapping. See Table 1.1 for a list of all channels.The range (distance) for 802.11b can vary widely, but each access point (with default antennas) typically covers a few hundred feet (indoors) or a few thousand feet (outdoors).With specialized, external antennas, this range can be greatly increased. 802.11b operates in the Industrial, Scientific, and Medical (ISM) unlicensed spectrum.

The top speed for 802.11b is 11 Mbps, but it will auto-negotiate down to rates of 5.5, 2, and 1 Mbps as the signal strength deteriorates.These speeds include a relatively high amount of “overhead,” as required by the protocol to operate. Keep in mind that actual throughput (for all 802.11 flavors) is typically about 50–60 percent of the advertised speeds. In other words, even under ideal circumstances, the actual data throughput (say, transferring a file) is usually around a maximum of 5–6 Mbps.
So many people have discovered the joys of wireless networking that 802.11b is quickly becoming a victim of its own success. Specifically, the level of Wi-Fi congestion found in any major metropolitan area is raising the RF noise floor and rendering many long distance links unusable.The pros and cons of 802.11b are as follows:

• Upside: Most popular and widely available; least expensive; good coverage
• Downside: Relatively slow speed; interference from other 2.4 GHz devices; only three nonoverlapping channels
  

The History and Basics of 802.11

The desire of people to communicate wirelessly spans many generations and technologies. Some might even argue that the ancient activity of lighting fires and using smoke signals was an early attempt to distribute a message without wires. In this book, however, we refer to the term “wireless” in the context of a modern data network. In other words: the ability to transmit and receive binary data from one location to another. A great deal of wireless data technology evolved in the late 20th century. Unfortunately, these wireless devices were typically proprietary and expensive.Their uses included specialized applications, such as remote cash registers and warehouse inventory systems.
After spending the better part of the 1990s engaged in technical discussions, the Institute of Electrical and Electronics Engineers (IEEE) ratified the 802.11 protocol in 1997.The original protocol supported three physical layer definitions: Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and InfraRed (IR).The supported data rates for DSSS and FHSS were 1 and 2 Mbps.These protocols operated in the 2.4 GHz unlicensed spectrum. IR remains an interesting footnote in the history of 802.11, as it never achieved any notable commercial success due to its limited range and line of sight requirements.
In 1999, the higher speed 802.11a and 802.11b protocols were ratified. 802.11b added 5.5 and 11 Mbps support using DSSS in 2.4 GHz, making it backwards-compatible with existing 1 and 2 Mbps DSSS gear (but not compatible with FHSS or IR equipment). 802.11a added Orthogonal Frequency Division Multiplexing (OFDM) as a modulation technique in the 5 GHz unlicensed spectrum, with speeds of up to 54 Mbps. In 2003, 802.11g was ratified, which provided higher speeds (up to 54 Mbps). 802.11g works by applying OFDM modulation techniques in the 2.4 GHz unlicensed spectrum. It remains backwards-compatible with 802.11b by integrating DSSS modulation (at 11, 5.5, 2, and 1 Mbps).