802.11a is a wireless networking standard created by the Institute of Electrical and Electronics Engineers (IEEE). It was designed to be an improvement over 802.11, which had been shown to have some security problems. 802.11a operates in the 5 gigahertz frequency range, which allows it to transmit data at speeds up to 54 megabytes per second (Mbps).
The IEEE has created three different types of 802.11a networks: Infrastructure, Ad-Hoc and Wireless Metropolitan Area Networks (WMANs). The infrastructure network uses a centralized wireless access point to provide internet connectivity for nearby users; while the ad-hoc is an independent system where computers communicate directly with each other without needing any type of central control or server device. A WMAN provides fixed high bandwidth service in areas that are too large for using ad hoc technology alone.
As early as 1999, the 802.11a standard had been created, in addition to 802.11b which was released around the same time. Most routers and wireless cards were made at that time using 802.11b, even though it only had an 11 Mbps data transfer rate. Because of this distinction, 802.11b remained more popular for the first few years than its sibling successor, 802.11a.
802.11g was introduced to the market in 2003, and both of the previous standards were finally being phased out for good. 802.11g was also released to support transfer rates up to 54 Mbps (like 802.11a) on the 2.4 GHz band (where as it had previously been positioned).
In order for 802.11a wireless to work, all devices on the network must support it.