1. In a wireless local area network having an access point station and user stations sharing access to a wireless transmission medium, a computer-implemented method of the access point station responding to a request from a user station for contention-based access of a new traffic flow of data packets from the user station to the wireless transmission medium when the wireless transmission medium is carrying a number of already admitted traffic flows of data packets, the already admitted traffic flows having quality of service requirements including maximum delay budgets and ratios of unsuccessfully delivered data packets tolerated by applications that receive the already admitted traffic flows, the method comprising the steps of: (a) obtaining quality of service requirements for the new traffic flow, the quality of service requirements including a maximum delay budget and a ratio of unsuccessfully delivered data packets tolerated by an application to receive the new traffic flow; (b) applying a model of the wireless local area network to estimate delay that the data packets will experience when delivered through the wireless local area network, in order to determine whether or not admission of the new traffic flow will violate the quality of service requirements of the new traffic flow or the already admitted traffic flows; and (c) admitting the new traffic flow upon determining that admission of the new traffic flow will not violate the quality of service requirements of neither the new traffic flow nor of the already admitted traffic flows.