A Token Based Distributed Algorithm for Medium Access in an Optical Ring Network

In this paper, we propose a node architecture and a token-based algorithm to access the shared medium in an optical ring network. The algorithm is based on a reservation scheme. However, unlike other reservation schemes which operate in three stages viz. reserve, transmit and release, the proposed scheme operates in two stages viz. reserve and transmit and does not explicitly release the reserved resources. The proposed algorithm selects the earliest available data-channel for reservation hence we call it earliest available channel (EAC) algorithm. The EAC algorithm operates in a distributed manner, and has the capability of handling channel collision and destination conflicts. Each node in the network maintains three modules: send module, receive module and token processing module, and is equipped with a tunable transceiver in contrast to the previous work which uses an array of fixed transceivers. We study the performance of the algorithm, by simulation, for fixed-sized bursts and bursts whose size is determined by M/Pareto distribution. We find our algorithm is superior in terms of wavelength utilization. Since, our algorithm uses a single tunable transceiver at each node, this is scalable with respect to the number of data-channels, however, delays are marginally increased. 2003 Elsevier B.V. All rights reserved.