ieee 802.11 wireless lans use a media access control protocol called carrier sense multiple access with collision avoidance (csma/ca). while the name is similar to ethernet's carrier sense multiple access with collision detection (csma/cd), the operating concept is totally different.

wifi systems are the half duplex shared media configurations, where all stations transmit and receive on the same radio channel. the fundamental problem of a radio system is that a station cannot hear while it is sending, and hence it is impossible to detect a collision. because of this, the developers of the 802.11 specifications came up with a collision avoidance mechanism called the distributed control function (dcf).

according to dcf, a wifi station will transmit only when the channel is clear. all transmissions are acknowledged, so if a station does not receive an acknowledgement, it assumes a collision occurred and retries after a random waiting interval.

the incidence of collisions will increase as the traffic increases or in situations where mobile stations cannot hear each other.