Rethinking Wireless MAC Architecture for Quality of Service Support – Design and Implementation

Existing wireless MAC standards are known to have fairness problems. In this paper, we ask a more fundamental question: should fairness be a property of medium access, or in other words, are we placing the blame on the right place? We argue that fairness is a property of applications and must be implemented by applications. Medium access control should simply provide mechanisms for application-defined fairness policies to be implemented effectively and efficiently. We argue that these mechanisms must provide separate control knobs for two main functions of MAC, namely, fairness control and contention resolution, in order to enable their independent evolution. Furthermore, they must be lightweight and their behaviors must be predictable to enable efficient and consistent implementations of fairness policies on top of these mechanisms. Existing MAC standards do not follow these guidelines. In this paper, we design a new MAC protocol, called Siren, adapted from an existing MAC protocol using these guidelines, and implement Siren in a real multi-hop wireless network. The efficacy of our design is demonstrated by implementing on top of Siren various popular fairness policies such as static priority, fair time sharing, proportional rate allocation, earliest deadline first (EDF) and proportional fairness and measuring their performance in our network testbed.