ation related to the type of frame, source and destination addresses, frame control, and sequence control. IEEE 802.11 standard defines three major frame types: (1) management frames which do not carry service data units, (2) control frames to assist delivery of data frames, and (3) some data frames with service data units, some without service data units, and a null frame to inform the access point of client's power save status. IEEE 802.11 physical layer is divided into two sublayers: physical layer convergence proto- col (PLCP) sublayer and physical medium dependent (PMD) sublayer (see Fig. 8.6). The PLCP sublayer receives a frame for transmission from the MAC sublayer and creates the PLCP protocol data unit (PPDU). The PMD sublayer then modulates and transmits the data as bits. The MAC protocol data unit that is delivered to the physical layer is referred to as the PLCP service data unit (PSDU). As part of the processing, the PLCP sublayer adds a preamble and header to the PSDU. When the PLCP layer receives the PSDU from the MAC layer, the appropriate PLCP preamble and header are added to the PSDU to create the PPDU. When transmitting data, the transmitting station provides the receiving station spe- cial synchronization sequences at the beginning of each transmission. The access point periodically broadcasts a special signal called beacon (once every 102.4 ms). When the Wi-Fi communication module is turned on, the device first detects and decodes the beacon signal and establishes physical synchronization with the sender. After establishing syn- chronization, the access point and the device initiate the authentication procedure followed by the association procedure. There are two types of scanning: passive and active scanning. As shown Fig. 8.8, during passive scanning, the device scans and detects the beacon signal from the access point and establishes synchronization based on the beacon signal. In the active scan mode, the device broadcasts a probe request to all access points or a specific one. If there is