A Wireless Local Area Network (WLAN) is composed of one (or several) access point(s) and wireless clients, such as Wi-Fi enabled laptop computers, tablet PCs, PDAs or Wi-Fi phones. Access Points are usually connected to a wired Local Area Network (LAN) to allow communications between the wireless clients and the rest of the wired network. We will refer to access point and wireless clients as 802.11 or Wi-Fi devices. Wi-Fi devices use microwaves to communicate, at the following frequencies:
802.11a/b/g technologies are designed for low power levels (<100mW). As a consequence, the coverage area of a given access point is limited to tenth of meters in a typical office space, or hundreds of meters in an outdoor set-up. To cover larger areas, it is necessary to add several access points to the network. For instance, the wireless infrastructure shown on the following diagram is made of two access points.