các hệ thống an toàn hơn. Vì lý do này người đọc mục tiêu là một trong những với một quan tâm đến bảo mật máy tính nói tin có sẵn từ thụ động nắm bắt thông thường Wi-Fi giao thông được biên dịch trong Bảng Bảng : Thông tin có sẵn từ một thực tế phân tích dữ liệu | . BACKGROUND 7 Figure a . Ad-hoc mode illustrated in Figure b is the second mode of operation. In ad-hoc mode all entities are considered clients. Ad-hoc mode may also be referred to as independent mode. Stations in ad-hoc mode participate in an ad-hoc network likewise if they are in infrastructure mode they participate in an infrastructure network. a Infrastructure. b Ad-hoc. Figure Modes of operation. To support communication over a wireless medium the wireless interface of a client or access point contains a radio and an antenna. To avoid interference and allow networks to operate in the same locations IEEE 22 specifies groups of frequencies that may be utilized by a network. Two groups are in the radio frequency band and one in the infrared band of the electromagnetic spectrum. The radio frequencies available to Wi-Fi are in the GHz Industrial Scientific and Medical ISM band and the 5 GHz Unlicensed National Information Structure U-NII band. Depending on regulatory authorities the range used by IEEE and is GHz and and GHz for IEEE . The IEEE standard divides the band into 14 channels but only three non-overlapping channels 22 Sec. . The 5 GHz band on the other hand is divided into 12 non-overlapping channels. A Wi-Fi network may operate in all of these channels but a single wireless interface may only operate in one channel. The data rate of a channel can be dynamically adjusted depending on the quality of the channel. The initial version of supported data rates up to 1 Mbps and 2 Mbps later 11 Mbps IEEE and up to 54 Mbps IEEE and . Some Wi-Fi equipment support data rates up to 108 Mbps by utilizing several channels at the same time Super G and Turbo G . The primary ideas in the IEEE specification to enable discovery and communication with other computers are the special beacon frames and probe request .
