hat indicated by the RTS frame minus the sum of the durations of one SIFS interval and CTS control frame (Figure 2.10). MAC Layer Station 1 Frame Access Point 3 SIFS + CTS + Data Frame + Ack Duration 2 SIFS + Data Frame + Ack Figure 2.10. Duration field for RTS and CTS control frames The Duration field of the ACK frame is set to ZERO in the case where the bit More Fragment is ZERO. In the case where this bit is at ONE, it contains the occupancy time of the radio channel for the transmission of the next fragment. It is equal to the sum of the durations of two SIFS intervals, a fragment and an ACK control frame (Figure 2.11). Station 1 Fragment X Fragment X+1 Access Point Fragment X 3 SIFS + 2 Ack + Fragment X+1 Duration ACK X 2 SIFS + Ack + Fragment X+1 Figure 2.11. Duration field for ACK control frame A station wakes up to recover data stored at the access point. It does not know the size of the pending data. The Duration field of the PS-POLL frame contains only the duration of one SIFS interval and an ACK control frame (Figure 2.12). Station PS-Poll Access Point PS-Poll SIFS + Ack Duration Figure 2.12. Duration field for the PS-POLL control frame 36 Wi-Fi Integration to the 4G Mobile Network 2.2.5. Frame fragmentation A MAC frame can be fragmented to reduce the impact of interference. In the case of a faulty reception, only the corrupted fragment is retransmitted, rather than the complete frame. Frame fragmentation is performed if the length of the frame is greater than a value defined by the network administrator. Fragments have the sequence number at the same value. The fragment number is incremented by one unit for each transmitted fragment. The More Fragment field (value of ONE) of the MAC header tells the receiver if other fragments will be transmitted. Fragments and control frames are separated by one SIFS interval to immobilize the radio channel during transmission of all fragments (Figure 2.13). Frag0 Fragl Backoff source destination Figure 2.13. Frame fragmentation 2.2.6. Standby management In order to 