Wireless LAN technologies do not allow collisions to be detected as they are in Ethernet environments because WLAN stations cannot hear jam signals due to their half-duplex functionality (i.e., they cannot listen and send at the same time). In order to suppress the negative effects of the half-duplex transmission, WLANs rely on the CSMA/CA mechanism (Carrier Sense Multiple Access with Collision Avoidance). Stations in the wireless LAN attempt to avoid collisions before they happen using a distributed coordinated function (DCF) that utilizes random backoff timers.
DCF requires a station wishing to transmit to listen for the channel status for a predefined interval. If the channel is found to be busy during that interval, the station defers its transmission. In a network where a number of stations contend for the wireless medium, if multiple stations sense that the channel is busy and defer their access, they will also virtually simultaneously find that the channel is released and then try to seize the channel. As a result collisions may occur. To avoid such collisions DCF also specifies random backoff, which forces a station to defer its access to the channel for an extra period. The access point is responsible for acknowledging client data and responds to successful transmissions by sending ACK packets.