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, 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
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.
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.
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
802.11 Throughput Varies
Speed is distance dependent. The farther away the remote device from the base station, the lower the speed . Also, the actual data throughput is generally no more than half of the rated speed because 802.11 uses a collision "avoidance" technology rather than collision "detection" as in wired Ethernet . 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.
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
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.
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.
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
802.11 Throughput Varies
Speed is distance dependent. The farther away the remote device from the base station, the lower the speed . Also, the actual data throughput is generally no more than half of the rated speed because 802.11 uses a collision "avoidance" technology rather than collision "detection" as in wired Ethernet . 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.
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