The Design and Evaluation of a Scalable Wireless MAC Protocol

Contention-based MAC protocols such as IEEE 802.11 DCF are known to perform well in a network with small number of nodes. As the number of nodes increases, the cost of collisions increases and dominates. This increasing collisions quickly drives every client in the network into wasted and unfair idleness, resulting in performance degradation. In this paper, we propose SMAC, a scalable MAC protocol, that preserves the advantages of 802.11 while avoiding its drawbacks. The design of SMAC leverages the efficient channel utilization of 802.11 DCF at low load and 802.11 PCF at high load. The SMAC-enabled AP controls the access of its clients by combining the contention and schedule-based access mechanisms and determining the optimal contention level among the clients. The SMAC-client simply indicates its intention of channel access. Through thorough analysis and evaluation, we show that SMAC preserves the channel utilization efficiency of 802.11 DCF, scales up to any number of nodes, and preserves perfect short-term and long-term fairness among the contending clients