save the battery consumption and increase its autonomy, the station can implement the standby mechanism. The station notifies the access point by transmitting a traffic frame (possibly a null frame) with the Power Management bit set to ONE. The station regularly listens for a beacon frame according to the information provided in the Listen Interval field of the ASSOCIATION management frame. The access point informs the station, via its BEACON channel, whether unicast, multicast or broadcast frames are pending (Figure 2.14). It is possible that, in the transmit interval of the beacon channel, the radio MAC Layer channel is busy. In this case, the station must extend the period of activity for the treatment of the beacon channel. TIM (Traffic Indication Map): this optional field of the BEACON management frame indicates to a station in standby that data is pending. These data are either unicast data (TIM information) or multicast data (DTIM information). This field has a variable length less than or equal to 256 bytes and is composed of the following subfields: - DTIM Count: this subfield indicates the number of BEACON frames before the next DTIM. When the value is zero, the TIM field contains DTIM information; - DTIM Period: this subfield indicates the number of BEACON frames separating two DTIM frames; - Bitmap Control and Partial Virtual Bitmap: these two subfields allow the identification of stations with pending data by the AID parameter. The station sends a PS-POLL frame to warn the access point. The latter can respond immediately after one SIFS or postpone the transfer. In all cases, the station must remain awake until data transfer. If more than one frame is waiting, then the access point informs the station via the More Data field in the MAC header (Figure 2.14). DTIM interval Beacon interval PS-POLL Unicast media Broadcast awake awake awake awake Station Figure 2.14. Standby management Wi-Fi Integration to the 4G Mobile Network 2.3. Security 2.3.1. Security mechanism The security of the radio interface sta