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An analytical model is proposed to describe the priority schemes of the EDCA mechanism of the IEEE 802.11e standard. EDCA provides class-based differentiated QoS to IEEE 802.11 WLANs. The main contribution of this paper opposed to other works is that the model predicts the throughput, delay and frame dropping probabilities of the different traffic classes in the whole range from a lightly loaded, non-saturated channel to a heavily congested, saturated medium. Furthermore, the model describes differentiation based on different AIFS-values, in addition to the other adjustable parameters (i.e. window-sizes, retransmission limits, TXOP lengths etc.) also encompassed by previous models. AIFS differentiation is described by a simple equation that enables access points to predict at which traffic loads starvation of a traffic class will occur. The model is calculated numerically and validated against simulation results …