Wireless Ethernet: 820.11a To 820.11g
The most common forms of wireless networking are built around various versions of the IEEE 802.11 wireless Ethernet standards, including IEEE 802.11b, IEEE 802.11a, IEEE 802.11g, and IEEE 802.11n.
Wireless Fidelity (Wi-Fi) is a logo and term given to any IEEE 802.11 wireless network product certified to conform to specific interoperability standards. Wi-Fi certification comes from the Wi-Fi Alliance, a nonprofit international trade organization that tests 802.11-based wireless equipment to ensure it meets the Wi-Fi standard. To carry the Wi-Fi logo, an 802.11 networking product must pass specific compatibility and performance tests, which ensure that the product will work with all other manufacturers’ Wi-Fi equipment on the market. This certification arose from the fact that certain ambiguities in the 802.11 standards allowed for potential problems with interoperability between devices. By purchasing only devices bearing the Wi-Fi logo, you ensure that they will work together and not fall into loopholes in the standards.
Note: The Bluetooth standard for short-range wireless networking, covered later in this chapter, is designed to complement, rather than rival, IEEE 802.11–based wireless networks.
The widespread popularity of IEEE 802.11–based wireless networks has led to the abandonment of other types of wireless networking such as the now-defunct HomeRF.
Note: Although products that are certified and bear the Wi-Fi logo for a particular standard are designed and tested to work together, many vendors of wireless networking equipment created devices that also featured proprietary “speed booster” technologies to raise the speed of the wireless network even further. This was especially common in early 802.11g devices, while newer devices conform more strictly to the official standards. Although these proprietary solutions can work, beware that most, if not all, of these vendor-specific solutions are not interoperable with devices from other vendors. When different vendor-specific devices are mixed on a single network, they use the slower common standard to communicate with each other.
When the first 802.11b wireless networking products appeared, compatibility problems existed due to certain aspects of the 802.11 standards being ambiguous or leaving loopholes. A group of companies formed an alliance designed to ensure that their products would work together, thus eliminating any ambiguities or loopholes in the standards. This was originally known as the Wireless Ethernet Compatibility Alliance (WECA) but is now known simply as the Wi-Fi Alliance (www.wi-fi.org). In the past, the term Wi-Fi has been used as a synonym for IEEE 802.11b hardware. However, because the Wi-Fi Alliance now certifies other types of 802.11 wireless networks, the term Wi-Fi should always be accompanied by the both the standards supported (that is 802.11a/b/g/n) as well as the supported frequency bands (that is 2.4 GHz and/or 5 GHz) to make it clear which products work with the device. Currently, the Alliance has certified products that meet the final versions of the 802.11a, 802.11b, 802.11g, and 802.11n standards in 2.4 GHz and 5 GHz bands.
The Wi-Fi Alliance currently uses a color-coded certification label to indicate the standard(s) supported by a particular device. The image below shows the most common versions of the label, along with the official IEEE standard(s) that the label corresponds to: 802.11a (orange background); 802.11b (dark blue background); 802.11g (lime green background); 802.11n (violet background).
The Wi-Fi Alliance’s certification labels for Wi-Fi–compliant 802.11 hardware.
IEEE 802.11b (Wi-Fi, 2.4 GHz band–compliant, also known as Wireless-B) wireless networks run at a maximum speed of 11 Mb/s, about the same as 10BASE-T Ethernet (the original version of IEEE 802.11 supported data rates up to 2 Mb/s only). 802.11b networks can connect to conventional Ethernet networks or be used as independent networks, similar to other wireless networks. Wireless networks running 802.11b hardware use the same 2.4 GHz spectrum that many portable phones, wireless speakers, security devices, microwave ovens, and the Bluetooth short-range networking products use. Although the increasing use of these products is a potential source of interference, the short range of wireless networks (indoor ranges up to approximately 150 feet and outdoor ranges up to about 300 feet, varying by product) minimizes the practical risks. Many devices use a spread-spectrum method of connecting with other products to minimize potential interference.
Although 802.11b supports a maximum speed of 11 Mb/s, that top speed is seldom reached in practice, and speed varies by distance. Most 802.11b hardware is designed to run at four speeds, using one of four data-encoding methods, depending on the speed range:
- 11 Mb/s—Uses quaternary phase-shift keying/complementary code keying (QPSK/CCK)
- 5.5 Mb/s—Also uses quaternary phase-shift keying/complementary code keying (QPSK/CCK)
- 2 Mb/s—Uses differential quaternary phase-shift keying (DQPSK)
- 1 Mb/s—Uses differential binary phase-shift keying (DBPSK)
As distances change and signal strength increases or decreases, 802.11b hardware switches to the most suitable data-encoding method. The overhead required to track and change signaling methods, along with the additional overhead required when security features are enabled, helps explain why wireless hardware throughput is consistently lower than the rated speed. The figure below is a simplified diagram showing how speed is reduced with distance. Figures given are for best-case situations; building design and antenna positioning can also reduce speed and signal strength, even at relatively short distances.
At short distances, 802.11b devices can connect at top speed (up to 11 Mb/s). However, as distance increases, speed decreases because the signal strength is reduced.
The second flavor of Wi-Fi is the wireless network known officially as IEEE 802.11a. 802.11a (also referred to as Wireless-A) uses the 5 GHz frequency band, which allows for much higher speeds (up to 54 Mb/s) and helps avoid interference from devices that cause interference with lower-frequency 802.11b networks. Although real-world 802.11a hardware seldom, if ever, reaches that speed (almost five times that of 802.11b), 802.11a relatively maintains its speeds at both short and long distances.
For example, in a typical office floor layout, the real-world throughput (always slower than the rated speed due to security and signaling overhead) of a typical 802.11b device at 100 feet might drop to about 5 Mb/s, whereas a typical 802.11a device at the same distance could have a throughput of around 15 Mb/s. At a distance of about 50 feet, 802.11a real-world throughput can be four times faster than 802.11b. 802.11a has a shorter maximum distance than 802.11b (approximately 75 feet indoors), but you get your data much more quickly.
Given the difference in throughput (especially at long distances), and if we take the existence of 802.11g out of the equation for a moment, why not skip 802.11b altogether? In a single word: frequency. By using the 5 GHz frequency instead of the 2.4 GHz frequency used by 802.11b/g, standard 802.11a hardware cuts itself off from the already vast 802.11b/g universe, including the growing number of public and semipublic 802.11b/g wireless Internet connections (called hot spots) showing up in cafes, airports, hotels, and business campuses.
The current solution for maximum flexibility is to use dual-band hardware. Dual-band hardware can work with either 802.11a or 802.11b/g networks, enabling you to move from an 802.11b/g wireless network at home or at Starbucks to a faster 802.11a office network.
IEEE 802.11g, also known to some as Wireless-G, is a standard that offers compatibility with 802.11b along with higher speeds. The final 802.11g standard was ratified in mid-2003.
Although 802.11g is designed to connect seamlessly with existing 802.11b hardware, early 802.11g hardware was slower and less compatible than the specification promised. In some cases, problems with early-release 802.11g hardware can be solved through firmware or driver upgrades.
Note: Although 802.11b/g/n wireless hardware can use the same 2.4 GHz frequencies and can coexist on the same networks, when mixing different standards on the same network, the network will often slow down to the lowest common denominator speed. To prevent these slowdowns, you can configure access points to disable “mixed mode” operation, but this will limit the types of devices that can connect. For example, you can configure a 2.4 GHz Wireless-N access point to allow 802.11b/g/n connections (full mixed mode), or to only allow 802.11g/n (partial mixed mode) connections, or to only allow 802.11n connections. The latter offers the highest performance for Wireless-N devices. Similarly you can configure Wireless-G access points to allow 802.11b/g (mixed mode) operation, or to only allow 802.11g connections. Restricting or disabling the mixed mode operation offers higher performance at the expense of restricting the types of devices that can connect.