PCF 802.11 Visualization

The Point Coordination Function (PCF) is a contention-free access method in IEEE 802.11 where an access point (AP) controls when stations can transmit. It operates using PIFS (PCF Interframe Space) and SIFS (Short Interframe Space) timing. The PCF period alternates with the DCF (Distributed Coordination Function) period to form a repetition interval.

Key Components:

• Repetition Interval: The cycle time that includes both PCF and DCF periods
• Beacon: Frame sent by AP to start the PCF period
• PIFS (PCF Interframe Space): Shorter than DIFS, used by AP to gain medium access
• SIFS (Short Interframe Space): Shortest IFS, used for immediate response frames
• NAV (Network Allocation Vector): Virtual carrier sensing mechanism showing when stations expect the medium to be busy

During PCF, the AP polls each station in turn, allowing contention-free transmission. Stations can only transmit when polled, whereas in DCF period, stations contend for access.