Wireless Networking Protocols

The primary technology used for building low-cost wireless networks is currently the 802.11 family of protocols, also known in many circles as Wi-Fi. The 802.11 family of radio protocols (802.11a, 802.11b, and 802.11g) have enjoyed an incredible popularity in the United States and Europe. By implementing a common set of protocols, manufacturers world wide have built highly interoperable equipment. This decision has proven to be a significant boon to the industry and the consumer. Consumers are able to use equipment that implements 802.11 without fear of “vendor lock-in”. As a result, consumers are able to purchase low-cost equipment at a volume which has benefitted manufacturers. If manufacturers had chosen to implement their own proprietary protocols, it is unlikely that wireless networking would be as inexpensive and ubiquitous as it is today.

While new protocols such as 802.16 (also known as WiMax) will likely solve some difficult problems currently observed with 802.11, they have a long way to go to match the popularity and price point of 802.11 equipment. As this equipment that supports WiMax is just becoming available at the time of this writing, we will focus primarily on the 802.11 family.

There are many protocols in the 802.11 family, and not all are directly related to the radio protocol itself. The three wireless standards currently implemented in most readily available gear are:

• 802.11b. Ratified by the IEEE on September 16, 1999, 802.11b is probably the most popular wireless networking protocol in use today. Millions of devices supporting it have shipped since 1999. It uses a modulation called Direct Sequence Spread Spectrum (DSSS) in a portion of the ISM band from 2.412 to 2.484GHz. It has a maximum rate of 11Mbps, with actual usable data speeds up to about 5Mbps.

• 802.11g. As it wasn't finalized until June 2003, 802.11g is a relative latecomer to the wireless marketplace. Despite the late start, 802.11g is now the de facto standard wireless networking protocol as it now ships as a standard feature on virtually all laptops and most handheld devices. 802.11g uses the same ISM range as 802.11b, but uses a modulation scheme called Orthogonal Frequency Division Multiplexing (OFDM). It has a maximum data rate of 54Mbps (with usable throughput of up to 25Mbps), and can fall back to 11Mbps DSSS or slower for backwards compatibility with the hugely popular 802.11b.

• 802.11a. Also ratified by the IEEE on September 16, 1999, 802.11a uses OFDM. It has a maximum data rate of 54Mbps, with actual throughput of up to 27Mbps. 802.11a operates in the ISM band between 5.745 and 5.805GHz, and in a portion of the UNII band between 5.170 and 5.320GHz. This makes it incompatible with 802.11b or 802.11g, and the higher frequency means shorter range compared to 802.11b/g at the same power. While this portion of the spectrum is relatively unused compared to 2.4GHz, it is unfortunately only legal for use in a few parts of the world. Check with your local authorities before using 802.11a equipment, particularly in outdoor applications. 802.11a equipment is still quite inexpensive, but is not nearly as popular as 802.11b/g.

In addition to the above standards, there are a number of vendor-specific extensions to equipment, touting speeds of 108Mbps, stronger encryption, and increased range. Unfortunately these extensions will not operate between equipment from different manufacturers, and purchasing them will effectively lock you into that vendor for every part of your network. New equipment and standards (such as 802.11n, 802.16, MIMO, and WiMAX) promise significant increases in speed and reliability, but this equipment is just starting to ship at the time of this writing, and availability and vendor interoperability is unclear.

Due to the ubiquity of equipment, better range, and unlicensed nature of the 2.4GHz ISM band, this book will concentrate building networks using 802.11b and 802.11g.