Design and Performance Evaluation of Scheduling Algorithms for Unslotted CSMA/CA with Backoff MAC Protocol in Multiple-Access WDM Ring Networks

The unslotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with backoff is a fully distributed, asynchronous Media Access Control (MAC) protocol for multiple-access Wavelength Division Multiplexing (WDM) ring networks with simplicity and robustness comparable to those of Ethernet [1,2]. In this paper we present the results of performance evaluation of four scheduling algorithms — Random Select (RS), Destination Priority Queueing (DPQ), Longest Queue First (LQF), and Shortest Packet First (SPF) — designed for the unslotted CSMA/CA with backoff MAC protocol to address the issues of fairness and bandwidth efficiency. Through extensive network-level simulations for a multiple-access WDM ring with 10 nodes and 10 wavelengths on a 100 km ring, we have verified that under uniform traffic condition, the LQF with optical buffer size of 13 and 78 octets shows the best performance in terms of fairness, guaranteeing full fairness (fairness index≈1) for arrival rates up to 9.5 Gbps/node, while for throughput and packet delay, the DPQ with the maximum optical buffer size of 1538 octets gives the best results. We have also identified that the optical buffer size greatly affects the performance of nonrandom scheduling algorithms.