Thomas Kunz
Systems and Computer Engineering
175
IEEE 802.11: DCF and PCF Coexistence
•PCF is optional, only
applicable in infrastructure network
•PCF has to coexist with
DCF, sits logically on top of DCF (see below)
•PCF relies on point
coordinator, which operates at the Access Point (AP)
•Point coordinator polls
stations and allows transmission without contending for channel
•CFP (contention-free
period) initiated by beacon after media has been idle for a PCF
Interframe
Space (PIFS), all stations will defer access for maximum duration of CFP
•Coordinator can poll
stations or prematurely terminate CFP by transmitting CFP-End frame