WLANs 802.11x technology and how it works

WLANs (802.11x)

WLAN technology is based on the 802.11 specifications, which have evolved in tandem with hardware capability. It is the most common form of wireless networking currently in use, largely due to its performance and ease of setup.

The IEEE 802.11 specifications were approved in 1997. The original goal was to provide wireless networking ability to hardware without requiring a large amount of set up time. "Mobility is handled at MAC layer, so handoff between adjacent cells is transparent to layers built on top of an IEEE 802.11 device" (Ferro, 2003, p. 5). The end result is that mobile devices can be treated as a generic networked device.

The original 802.11 standard quickly became obsolete, and was replaced by 802.11b. While 802.11 legacy devices transferred data at either 1Mb/s or 2Mb/s (Megabits per second), 802.11b devices transfer at 5.5 or 11 Mb/s.

Later in 1997, the IEEE published the specifications for 802.11a, a revision of 802.11a that allowed for transfer speeds up to 54Mb/s and operates near the 5 Ghz band. This band is unlicensed in the United States, but not in many other companies. Devices using this standard cannot be used in Europe because of spectrum licensing restrictions (Ferro, 2003, p.6).

Several years later, the 802.11g standard was released. 802.11g boasts the performance of 802.11a devices, but because it operates in the 2.4Ghz band, it is able to be used in Europe.

Regulations

WLAN technology is based on the 802.11 specifications, which have evolved in tandem with hardware capability. It is the most common form of wireless networking currently in use, largely due to its performance and ease of setup.

With the exception of 802.11a, Wi-Fi setups operate in the spectrum near 2.4ghz. This is a standardized frequency that is unlicensed by international agreement. There are, however, restrictions on broadcasting. Broadcasts must be under a certain power and has a set number of channels. These specifications are particularly strict in the United States. Channels are 22 Megahertz wide, and there is a 5 Megahertz gap between each channel to prevent channel overlapping.

Structure

Wi-Fi setups typically consist of at least one access point and at least one client. Access points are pieces of hardware that broadcast and receive signals. They are typically stationary, and hardwired to the uplink source. The exception is Wireless Access Points (WAP), devices that are used primary to extend signal over a larger area by re-transmitting the signal. The access point transmits its SSID (an acronym for "Service Set Identifier") every tenth of a second (100ms) at 1MB/s. This low transmission rate ensures that any client can receive the signal. The signals are short and have very little effect on performance.

These signals, called "beacons" identify the access point to the client. The 802.11 standard does not include criteria for connection interfacing; it is entirely up to the client. This is an advantage of Wi-Fi, opening up the standard for flexible innovation; however, it can also be a drawback, because the performance of wireless adapters may vary widely with the manufacturer or model.

802.11b was the protocol that popularized WLAN. It allowed sufficient speeds for the protocol to be useful, with a theoretical maximum of 11Mb/s and a practical maximum of about 6Mb/s -- over six times the typical bandwidth of legacy 802.11b -- and was quickly adopted by hardware manufacturers.

802.11a was approved in 1999 and uses the same protocol as legacy 802.11. It improves on 802.11b by using 52-subcarrier orthogonal frequency-division multiplexing (OFDM). This technology uses multiple narrow bands of radio frequency, and concentrates on minimizing interference between bands (crosstalk) instead of perfecting individual bands. While the advertised maximum throughput was 54Mb/s, typical throughput is realistically around 20Mb/s.

802.11g was the third ratified amendment of the 802.11 specification. This 2003 revision uses technology similar to 802.11a, but uses the unlicensed 2.4Ghz spectrum. Although the theoretical maximum bandwidth is the same as 802.11a, improvements in compression techniques and modulation schemes boosted the typical bandwidth to about 25Mb/s.

Unfortunately, many years of development using the same frequency is causing a new problem. So many devices use this frequency that it is becoming increasingly common for products to interfere with each other. Not only do WLAN products use this range, but also microwave ovens, Bluetooth devices, and many cordless phones.

802.11n is expected to be officially approved in July of 2007, and should be over ten times faster than 802.11a or 802.11g (Mitchell, 2006). Devices supporting the standard have already emerged on the market, however, owing to expected typical data throughput rates of 200Mb/s.

This speed increase will be accomplished using a technology known by the acronym "MIMO," which stands for "multiple-input multiple-output," and operates by using more than one transmitter and receiver antennae.

802.11x is the generic term used for all 802.11 specifications. Current proposed specifications are documented by Wikipedia, a source which, despite attacks on its reliability, tends to be quite dependable in technological areas due to its writing base. All details have been confirmed by a secondary source. Said specifications are as follows:

IEEE 802.11 -- Original specification (1999)

IEEE 802.11a -- 54Mb/s, 5 Ghz frequency (1999)

IEEE 802.11b -- Enhancement to 802.11 to support 11Mb/s (1999)

IEEE 802.11c -- Bridge operation procedures (2001)

IEEE 802.11d -- International roaming extensions (2001)

IEEE 802.11e -- QoS enhancements, including packet bursting (2005)

IEEE 802.11F -- Inter-access Point Protocol (2003, withdrawn Feb. 2006)

IEEE 802.11g -- 54Mb/s standard, backward compatible with 802.11b (2003)

IEEE 802.11h -- Spectrum-managed 802.11a for European Compatibility (2004)

IEEE 802.11i -- Enhanced security protocol (2004)

IEEE 802.11j -- Extensions for Japan (2004)

IEEE 802.11k -- Radio resource measurement enhancements (proposed)

IEEE 802.11l -- Reserved, will not be used

IEEE 802.11m -- Maintenance of standard, miscellaneous additions (ongoing)

IEEE 802.11n -- 540Mb/s maximum throughput standard using MIMO (proposed)

IEEE 802.11o -- Reserved, will not be used

IEEE 802.11p -- Wireless access for vehicles (proposed)

IEEE 802.11q -- Reserved, will not be used

IEEE 802.11r -- Rast roaming (proposed)

IEEE 802.11s -- ESS Mesh Networking (proposed)

IEEE 802.11T -- Test methods and metrics (proposed)

IEEE 802.11u -- Intercompatibility with non-802.11x networks (proposed)

IEEE 802.11v -- Wirless network management (proposed)

IEEE 802.11w -- Protected management frames (proposed)

IEEE 802.11x -- Reserved, will not be used

IEEE 802.11y -- 3650-3700 Operation in the U.S. (proposed)

802.11F and 802.11T are not amendments, but documents in their own right, and thus are capitalized.

Alternatives

While WLAN is certainly the most common networking protocol, many wireless devices use other protocols. Each has its own advantages and disadvantages, but none are as widely known and used as Wi-Fi.

Alternatives: Bluetooth

Bluetooth is a frequency-hopping wireless technology that is able to broadcast wirelessly with very little power. It is most often used for peripheral devices such as computer mice. The range is about ten meters. The throughput is significantly less than modern 802.11 standards; all estimates are below 1Mb/s, and some guess at only 30Kb/s.

Alternatives: 3G

3G is a third-generation technology frequently used for cellular networks. Because of the application, it can be described as a "vertically integrated, top-down, service-provide approach to delivering wireless internet service" (Lehr, 2003, p.353). Because cell phone communicate to each other via high-level hubs, direct communication between devices is unnecessary.