802.11a

Unlike 802.11b and 802.11g, 802.11a operates in the 5 GHz radio band, instead of the2.4 GHz band. Because of this, 802.11a is not compatible with 802.11b or 802.11g devices, and upgrading your WLAN to 802.11a will require you to purchase new equipment. However, you can purchase dual-band access points that use both radio frequencies and can operate on both 802.11b and 802.11a WLANs.

Although 802.11a has a maximum data rate of 54 Mbps, actual throughput seldom exceeds 35 Mbps, and is often less than 20 Mbps. Usually, 802.11a can only achieve its top connection speed if the distance between adapter and access point is less than 30 feet. Because of its short range, 802.11a may not be your best choice if you have to cover a wide area with Wi-Fi access. Doing so will require you to buy more access points than another standard might require (specifically 802.11g).