A distributed medium access protocol for wireless LANs

The Urn protocol has been proposed for distributed access to the radio medium. Access rights to the channel are determined at each station through estimation of the total network load. The Urn´s performance was shown to be similar to that of Slotted Aloha at light load while defaulting to TDMA-like behavior under heavy load. We simulated the Urn protocol in a realistic radio environment, taking into account channel effects such as fading, capture, collisions, hidden nodes, and noise. We quantify the resulting disparity of traffic load estimation across users. We propose techniques for reducing this divergence. We also extend the throughput-delay results to include peer-to-peer and centralized server situations, through nonuniform traffic and priority considerations. We show the throughput of the Urn scheme to be high under all these effects. Introducing two classes of priority service reduces the average delay experienced by the high priority users