An access contention scheme having both multi-level priorities and a contention-free access indicator for use by a station in a network of stations. When a contention control indicator is detected for a contention period, a station having a frame to transmit determines from the contention control indicator...http://www.google.co.uk/patents/US7352770?utm_source=gb-gplus-sharePatent US7352770 - Media access control protocol with priority and contention-free intervals
