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This paper proposes a comprehensive but tractable model of IEEE 802.11 carrying traffic from a mixture of saturated and unsaturated (Poisson) sources, with potentially different quality-of-service (QoS) parameters, i.e., TXOP limit, CWmin , and CWmax. The model is used to investigate the interaction between these two types of sources, which is particularly useful for systems seeking to achieve load-independent “fair” service differentiation. We show that, when the TXOP limit for unsaturated sources is greater than one packet, batches are distributed as a geometric random variable clipped to TXOP limit. Furthermore, we present asymptotic results for access delay distribution, which indicates that it is infeasible to obtain real-time service in the presence of eight or more saturated sources, regardless of the real-time traffic load, given that all stations use a CWmin of 32.
Date of Publication: Jan. 2012