Point Coordination Function (PCF)

Point coordination function (PCF) is an optional technology used to prevent based on Wi-based on IEEE 802.11conflict in the WLAN standard. It is a MAC (Media Access Control) sub-layer technology used for using carrier sense multiple access (CSMA) with collision avoidance (CA) / Area of CA)

PCF is used together with the mandatory Distributed Coordination Function (DCF). It is used in centralized control systems and exists in the access points (AP) of the wireless network. The AP is usually a wireless router that coordinates network communication.

Features of PCF

• It is an optional feature that sits on top of the mandatory DCF. PCF and DCF run simultaneously.

• It uses polling and response methods to provide channel access to sites, thus eliminating the need for contention.

• Polling is completed by the point coordinator (PC) residing in the central access point (AP).

• The site waits for the PIFS (Point-to-Frame InterFrame Space) before transmission. PIFS is usually less than the DIFS (Distributed InterFrame Space) used in DCF.

• The PC polls in a round-robin manner to provide access to sites in the wireless network.

• The AP sends a special control frame called a beacon frame to start and repeat polling.

Technology

• Steps1 -The PC sends a beacon frame after waiting for the PIFS. The beacon frame reaches each site in the wireless network.

• Steps2-If the AP has data for a specific site (such as site X), it sends data and authorization to site X.

• Steps3-When site X receives permission from the AP, if it has data frames for the AP, it sends data and acknowledgment (ACK) to the AP.

• Steps4 -After the AP receives data from site X, it sends an ACK to it.

• Steps5-Then, the AP sends to the next site, which is site Y. If the AP has data for Y, it sends data and authorization to Y, otherwise, it only sends authorization to Y.

• Steps6-When the AP receives permission, site Y sends its data (if any) to the AP.

• Steps7-This process continues for all sites in the polling.

• Steps8-Finally, after granting access to all sites, AP sends ACK to the last site. Then, it notifies all sites that the polling has ended.