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Access Point Supporting PCF – (Contention Free Parameter)

By George Stafanick, Blog Contributor
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A VIP user was complaining about WiFi connectivity issues. It appeared to be local to this user and no one else. Users in the immediate area weren't reporting a problem. I do about 60 minutes of captures and the user doesn't have a problem the entire time. Typical, "motor is knocking bring it to the shop and it doesn't knock."   

During the capture something caught my eye. Something rather interesting. The examination of a  neighboring beacon from a Cisco-Linksys access point I seen the "Contention Free Parameter Set". At first I thought it was a CRC. But after closer examination and reviewing other beacons it was indeed legit.  It would appear at some level the access point might be supporting PCF (Point Coordination Function). 

PCF is this mythical creature. Legend has it, few if any vendors supported it. Interestingly enough, here it is. It's not a CRC. Not sure to what level this is implemented. 

contention.free.period.png

I was curious to see if any clients were actually supporting PCF and associated, but I didn't see any. I filtered the traffic and a CFE (Contention Free End) frame could be seen from time to time. Again, not a CRC.

contention.free.period.2.jpg

Reference: http://community.arubanetworks.com/t5/Airheads-Dictionary/PCF-Point-Coordination-Function/ta-p/221738

Im curious has anyone else seen this or PCF in the wild ?