802.11 - Computer Definition
The family of IEEE standards describing the over-the-air interfaces for a number of wireless local area networks (WLANs).Variously referred to in the vernacular as Wi-Fi (Wireless Fidelity) and Wireless Ethernet (the Ethernet CSMA/CA protocol is used in 802.11), 802.11 standards include infrared (IR) and radio frequency (RF) solutions, although there currently appear to be no practical applications for IR.The RF standards fall into the 2.4 GHz and 5 GHz ISM bands and offer theoretical bandwidth up to 54 Mbps. The original 802.11 standard (1997) operated in the 2.4 GHz band and supported theoretical data rates up to 2 Mbps. This early standard included a great number of options, which made interoperability of products difficult, or at least uncertain. As a result, 802.11 never gained any real traction in the market. Soon afterward, however, much improved extensions to 802.11 were finalized, and WLANs quickly gained in popularity. Current extensions include 802.11a, 802.11b, and 802.11g. Still under development is 802.11n. See also 802.11a, 802.11b, 802.11g, 802.11n, CSMA/CA, Ethernet, IEEE, ISM, RF, Wi-Fi, Wi-Fi5, and WLAN.
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A family of IEEE standards that extend the common wired Ethernet local network standard into the wireless domain. The 802.11 standards are widely known as "Wi-Fi" because the Wi-Fi Alliance provides certification for 802.11 products. There have been four major 802.11 standards designated with letter suffixes (a, b, g and n); the latest and fastest being 802.11n (the slowest is 802.11b, and the two medium speed are 802.11a and 802.11g). For more about Wi-Fi networks, see wireless LAN and Wi-Fi. Following are the 802.11 specifications, from slowest to fastest. Very Slow Speeds (1997) The first 802.11 specifications included two spread spectrum methods in the unlicensed 2.4 GHz band: 1 Mbps frequency hopping (FHSS) and 1 and 2 Mbps direct sequence (DSSS). It also included an infrared method. Both FHSS and infrared were dropped by the Wi-Fi Alliance, but 1 Mbps DSSS method is still used by access points to advertise themselves (see beaconing). 11b (1999) - Slow Speed Using DSSS and the 2.4 GHz band, 802.11b boosted speed to 11 Mbps while retaining the slower DSSS modes to accommodate weak signals. It was the first major wireless local network standard, and many laptops were retrofitted with 11b network adapters. Later, 11b was built into the laptop motherboard. 11a (1999) - Medium Speed Using orthogonal FDM (OFDM), 802.11a transmits up to 54 Mbps. It uses the 5 GHz band and is not backward compatible with the slower 11b. 11g (2003) - Medium Speed Using orthogonal FDM (OFDM) transmission, 11g increased speed from 11 to 54 Mbps. Both 11b and 11g use the 2.4 GHz band and are compatible, which is why equipment is often designated as 802.11b/g. If 11b and 11g devices communicate, it is done at the slower 11b speed. 11n (2009) - Highest Speed The 802.11n standard uses multiple antennas for speeds of 300 Mbps and more. Since 11n can operate in both spectrum bands, it is compatible with previous 11b/g and 11a standards (see 802.11n). 11ac (2012) - Faster Yet 802.11ac operates in the 5 GHz band and, using multiple antennas and, depending on the number of antennas, can achieve data rates into the gigabit range (see 802.11ac). Multiple Channels To allow nearby access points to operate without interference, 802.11 divides the spectrum into 19 channels for 11n, 12 for 11a and only three for 11b and g. The 11b/g standards use overlapping channels, and only channels 1, 6 and 11 can be used in the U.S. Two 802.11 Modes: Infrastructure and Ad Hoc In "infrastructure" mode, wireless devices communicate to a wired LAN via base stations known as "access points." Each access point and its wireless devices are known as a Basic Service Set (BSS). An Extended Service Set (ESS) is two or more BSSs in the same subnet. In "ad hoc" mode, also known as "peer-to-peer" mode, wireless devices communicate with each other directly without an access point. This is an Independent BSS (IBSS). An additional mode was added in 2009 that enables two devices to communicate with each other directly (see Wi-Fi Direct). 802.11 Throughput Varies Speed is distance dependent. The farther away the remote device from the base station, the lower the speed (see chart below). Also, the actual data throughput is generally no more than half of the rated speed because 802.11 uses a collision "avoidance" technology (see CSMA/CA) rather than collision "detection" as in wired Ethernet (see CSMA/CD). Wired systems can detect collisions, but wireless cannot and thus waits for an acknowledgment to determine if the packet was transmitted properly. For example, a rated 54 Mbps yields about 27 Mbps in real throughput. See 802.11 timeline, wireless LAN, ISM band, CCK/OFDM, 802.16 and 802.15. 802.11 VERSION Max* Indoor Bands Speed Range Encoding (GHz) (Mbps) (ft) 11b DSSS 2.4, 5 11 150 11g OFDM 2.4 54 170 11a OFDM 5 54 95 11n OFDM 2.4, 5 150** 230 11ac OFDM 5 433*** 230 * = Outdoor 2x to 4x farther. ** = Per antenna. *** = Per antenna at 80 MHz channels. (See 802.11ac.)
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