In 1998, Giuseppe Bianchi introduced a mean field Markov model of the fundamental medium access control protocol used in Wireless Local Area Networks (WLANs). Due to the model’s intuitive appeal and the accuracy of its predictions, since then there has been a vast body of material published that extends and analyzes models of a similar character. As the majority of this development has taken place within the culture and nomenclature of the telecommunications community, the aim of the present article is to review this work in a way that makes it accessible to probabilists. In doing so, we hope to illustrate why this modeling approach has proved so popular, to explain what is known rigorously, and to draw attention to outstanding questions of a mathematical nature whose solution would be of interest to the telecommunications community. For non-saturated WLANs, these questions include rigorous support for its fundamental decoupling approximation, determination of the properties of the self-consistent equations and the identification of the queueing stability region. 1

1.1 Overview of 802.11...................................... 1 1.1.1 Contention mechanisms............................... 2 1.1.2 DCF contention mechanism............................. 3

Abstract—Designing efficient yet flexible medium access controllers (MAC) for wireless protocols is a challenge. Not only are these protocols still evolving, they are also increasingly demanding in terms of throughput and real-time requirements. In order to support a careful application-driven architecture development, reference applications are required that expose the full system and enable the quantitative evaluation of performance-flexibility tradeoffs. For this purpose, we have captured the 802.11n MAC protocol in an executable reference application which comprises the system function and its environment including traffic scenarios. We model the reference in Click, a packet processing framework. The functionally-correct model captures performance-relevant aspects such as the wireless protocol timing exactly. Leveraging extensions to Click we can use the model for the development and deployment of embedded architectures. Our 802.11n MAC model comprises between 118 and 1238 functional elements and can be simulated in real time depending on the scenario. Due to its modularity, additional scenarios can be added productively. I.

An overwhelming part of research work on wireless networks validates new concepts or protocols with simulation or analytical modeling. Unlike this approach, we present our experience with implementing the Idle Sense access method on programmable off-the-shelf hardware—the Intel IPW2915/abg chipset. We also present measurements and performance comparisons of Idle Sense with respect to the Intel implementation of the 802.11 DCF (Distributed Coordination Function) standard. Implementing a modified MAC protocol on constrained devices presents several challenges: difficulty of programming without support for multiplication, division, and floating point arithmetic, absence of support for debugging and high precision measurement. To achieve our objectives, we had to overcome the limitations of the hardware platform and solve several issues. In particular, we have implemented the adaptation algorithm with approximate values of control parameters without the division operation and taken advantage of some fields in data frames to trace the execution and test the implemented access method. Finally, we have measured its performance to confirm good properties of Idle Sense: it obtains slightly better throughput, much better fairness, and significantly lower collision rate compared to the Intel implementation of the 802.11 DCF standard.