Experimental evaluation of MAC protocols for fairness and QoS support in wireless networks

Existing wireless MACs are known to have fairness and QoS problems 1. In response, the wireless community have come up with numerous ldquopoint solutionsrdquo, with one-to-one comparison of their solution with existing MACs for the specific fairness model they target. However, with some tradeoff of flexibility and efficiency, many of these MACs can be made relatively free of a a specific fairness model. This decoupling of the MAC from the fairness model is desirable because it allows objective testing of the MAC under different fairness models and also allows independent evolution of fairness policies and research into medium access issues. However, there is no cross-model evaluation of such MACs especially in the context of real multihop wireless testbeds. In this paper we address this issue by testing three MACs - 802.11e, EY-NPMA and DWOP, (which represent different ways of enabling fairness in the MAC) across a number of fairness and QoS models - temporal/rate and proportional fairness, and EDF and static priority scheduling. In the process we also extend EY-NPMA significantly (which we call Siren) for multihop wireless environments. We perform these comparisons on a 30 node multihop wireless sensor testbed comprising of MicaZ devices equipped with the CC2420 radio.