anagement frames, namely ASSOCIATION REQUEST, ASSOCIATION RESPONSE, REASSOCIATION REQUEST and REASSOCIATION RESPONSE. These frames introduce new fields (Figure 2.5). Association Request Listen Supported Interval Rates Listen Current AP Reassociation Request Supported Interval Address Rates Association Response Status Association Supported Reassociation Response Rates Frame Destination Source Duration BSSID Message Control Address Address Figure 2.5. Structure of management frames relating to the association phase Listen Interval: this field is coded on 16 bits. It contains the value of the number of BEACON frames during which the station will remain in standby. The access point uses this information to estimate the size of the buffer needed to store the data. Current AP Address: this field is coded on six bytes and contains the MAC address of the access point. This field is used when the station changes the access point. It indicates the address of the old access point to the new one SO that the latter can retrieve the stored data. AID: this field is coded on 16 bits and contains the identifier of the station allocated by the access point. The DISASSOCIATION and DEAUTHENTICATION management frames are used to terminate association and authentication, respectively. They contain a 16-bit field, indicating the reason for the shutdown (Figure 2.6). Wi-Fi Integration to the 4G Mobile Network Frame Destination Source Duration BSSID Message Control Address Address Reason Code Figure 2.6. Structure of the management frames DISASSOCIATION and DEAUTHENTICATION 2.2. Procedures 2.2.1. Timers The transmission of several frames is separated by an inter-frame interval. Several types of intervals are defined, each determining a priority level: - SIFS (Short Inter-Frame Space): this interval corresponds to the highest priority level. It is used following the RTS and CTS control frames and the traffic frame; - DIFS (DCF Inter-Frame Space): this interval has a longer duration (DIFS = SIFS + 2 ST (Slot Time)). It is used following an