A distributed fairness algorithm for bus-based metropolitan optical network

In this paper, we focus on the performance of asynchronous carrier sense multiple access with collision avoidance (CSMA/CA) protocol with variable packet sizes. We examine the fairness issue arising between ring nodes sharing a common data channel and show that the asynchronous CSMA/CA protocol suffers from bandwidth fragmentation and positional priority fairness problems. The paper proves that the phenomenon of bandwidth fragmentation represents the most important issue on asynchronous CSMA/CA protocol because it leads to bandwidth waste and thus increases unfairness for certain ring nodes. In this regard we explore limitations of a previous proposed solution, the so called traffic control architecture using remote descriptors (TCARD). Afterwards, we present an algorithm called Smart PACEd Transmission (SPACES) which deals with the aforementioned fairness problems. The desired scheme is based on a statistical and fully distributed mechanism to grant fair access to shared resources. As illustrated in this article SPACES alleviates performance degradation and resources underutilized while achieving fairness among ring nodes