Activity polling and activity contention in media access control protocols

This paper compares activity polling mechanisms occurring in a class of media access control (MAC) protocols for passive tree or star networks. An analytical model is developed which explains the function of polling mechanisms in MAC protocols for the single source case, i.e., with one on-off source present in the whole system. Results from this model are compared to simulation results for the single source case and for multiple source cases. It is shown that these analytical results can furthermore explain the main effects seen under normal load, and the analysis is extended to a contention based mechanism, leading to a fair parametric comparison between activity polling and activity contention under comparable conditions. The final result quantifies the range of parameters (round-trip time and fraction of active stations) where a contention mechanism can give better delay quantile performance than a polling mechanism.