Systems and methods which provide network congestion avoidance implementing a fairness scheme in which a cost function is used are shown. Transmission cost, for use in network congestion avoidance packet dropping decisions, may be determined from an amount of air time needed to transmit a data packet, a transmission data rate, a size of a packet, an amount of spectral energy or transmit power associated with transmission, etc. A packet dropping probability for a particular packet is preferably determined as a function of the current flow cost and average flow cost to provide fair allocation of network communications resources. Embodiments additionally implement buffer based packet dropping probability calculation in order to provide a robust network congestion avoidance technique. Cost based packet dropping probability calculation and buffer based packet dropping probability calculation implemented according to embodiments are adapted to accommodate quality of service applications.