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802.11 versionsFollowing is a summary of the IEEE 802.11 Wi-Fi standards, from newest to oldest. See 802.11 and Wi-Fi.
11ac (2012) - Highest Speed
802.11ac operates in the 5 GHz band with data rates into the gigabit range (see 802.11ac). Very valuable when multiple users are online at the same time.
11n (2009) - High Speed
802.11n uses multiple antennas for speeds up to 450 Mbps. 11n operates in both spectrum bands and is compatible with previous 11b/g and 11a standards (see 802.11n). More than enough speed for the casual user.
11g (2003) - Medium Speed
Using orthogonal FDM (OFDM) transmission, 11g increased speed in the 2.4 GHz band to 54 Mbps. Both 11b and 11g are compatible, and equipment is often designated as 802.11b/g. If b and g devices communicate, it is at the slower 11b speed. See OFDM.
11a (1999) - Medium Speed
Using orthogonal FDM (OFDM), 802.11a transmits up to 54 Mbps. It uses the 5 GHz band and is not compatible with 11b.
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.
Very Slow (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).