Fiber-optic interconnection of local area networks: physical limitations of topologies

Abstract

This paper examines and quantifies the physical limitations imposed by basic topologies and access couplers in fiber-optic interconnection of local area networks (LAN's). To that end a detailed comparison of the basic topologies and access couplers is provided. The comparison is in terms of amount of fiber required, average propagation delay, fault tol- erance, maintainability, number of access couplers required, and maximum bit rate. These results lead to simple guidelines for the choice of topology and the type of access couplers that may be used in practical LAN interconnection. Our results indicate that for 100 node LAN interconnection, the star topology requires 3.8 times as much fiber as a dual ring, which may be of significant concern if the interconnection network is in an urban business area. The average propagation delay of a dual ring for a 100 node interconnection, on the other hand, is 3.3 times that of the star. This may be a significant disadvantage in LAN interconnection networks where the distance between nodes is large. The maximum bit rate, by assuming simple direct detection, is calculated for a fiber network based on the topology and type of access coupler. Our results show that the more fault tolerant an access coupler is, the lower is the maximum bit rate it can support.