Distributed coordination function

Distributed coordination function (DCF) is the fundamental medium access control (MAC) technique of the IEEE 802.11-based WLAN standard (including Wi-Fi). DCF employs a carrier-sense multiple access with collision avoidance (CSMA/CA) with binary exponential backoff algorithm. DCF requires a station wishing to transmit to listen for the channel status for a DIFS interval. If the channel is found busy during the DIFS interval, the station defers its transmission. In a network where a number of stations contend for the wireless medium, if multiple stations sense the channel 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. In order 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 length of the backoff period is determined by the following equation: B a c k o f f T i m e = r a n d o m ( ) × a S l o t T i m e {displaystyle mathrm {BackoffTime} =mathrm {random} () imes mathrm {aSlotTime} }