SIMULATION OF TOKEN LESS PROTOCOLS FOR FIBER OPTIC LANs

Abstract

Recent years have witnessed a rapid growth in local area communication needs due to the increase in user demands and the emergence of new applications such as real time voice and video, high-speed printers, and graphics. LAN designers now, are being urged to provide systems able to handle very high through-put among users several kilometers apart, while still satisfying delay constraints which become severe when real-time traffic is involved. A suitable choice of transmission medium, topology and access protocol is necessary to meet these demands. Fiber optic transmission technology is presented, and the various topologies, and protocols suitable for the fiber optic LANs have been described. The two classes of collision avoidance LANs are presented : explicit token passing and implicit token passing In explicit token passing networks, a station requires a special permit, called a token, before it can transmit its message. In implicit token passing networks, no special permit is required. Instead, stations depend on a set of network events to schedule their transmission. The attributes of various topologies and access protocols for these fiber optic LANs are described and compared in terms of network nodes, bandwidth utilization and transport and access delay. A methodology for evaluating the performance of a family of, recently developed implicit token. protocols called Token less Protocols is presented. The LAN consists of a pair of unidirectional fiber optic buses to which stations are connected via passive taps. The protocols provide round-robin bounded delay V access to all stations. Contrary to most round-robin bounded delay access schemes, the protocols do not require transmission of special packets (tokens); rather, they simply rely on the detection of bus activity at each station. The performance of these protocols in various traffic 1conditions and system-configu-rations is evaluated via analysis and simulation. The performance parameters considered are bus utilization and insertion delay