Point Coordination Function (PCF) is an access method for collision-free access to a WLAN according to 802.11e that works with a coordinator. In this procedure, similar to the Token Ring, a deterministic media access is selected.
In the PCF method, which forms an alternative access method to Distributed Coordination Function( DCF), it must be ensured that stations accessing using the DCF method do not collide with those using the PCF method.
In the PCF method, an access point( AP) forms the coordinator and polls each station in turn that is in the same Basic Service Set( BSS). The station is not allowed to transmit until it is addressed by the access point (AP), in which case the access point establishes a contention free period( CFP). This is a contention free period during which it is not allowed to transmit.
If possible, all stations in a WLAN should operate with PCF function. However, implementation of the PCF function is optional. In industrial WLANs, the Industrial WLANs( IWLAN), the industrial Point Coordination Function( iPCF) must fulfill real-time transmissions.