Point Coordination Function
- Point Coordination Function
Point Coordinated Function is a Media Access Control (MAC) technique used in wireless networks which relies on a central node, often an Access Point (AP), to communicate with a node listening, to see if the airwaves are free (ie, all other nodes are not communicating). [citeweb|title=Point Coordination Function (PCF)|url=http://www.wireless-center.net/WLANs-WPANs/1436.html|publisher=wireless-center.net|accessdate=2008-02-26]
Since most APs have logical bus topologies, (they are shared circuits) only one message can be processed at one time (it is a contention based system), and thus a media access control technique is required.
The problem with wireless is that there is a hidden node problem, where some regular nodes (which communicate only with the AP) cannot see other nodes on the extreme edge of the geographical radius of the network (because the wireless signal attenuates before it can reach that far). Thus having an AP in the middle allows the distance to be halved, allowing all nodes to see the AP and consequentially, halving the maximum distance between two nodes on the extreme edges of a circle-star topology.
PCF simply uses the AP as a control system in wireless MAC.
PCF seems to be implemented only in very few hardware devices as it is not part of the Wi-Fi Alliance's interoperability standard.
See also
* Contention free pollable
* Distributed Coordination Function
* Hybrid Coordination Function
References
External links
* [http://www.wi-fiplanet.com/tutorials/article.php/1548381 802.11 Medium Access Methods on wi-fiplanet.com]
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