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

The physical limitations imposed by basic topologies and access couplers in fiber-optic interconnection of local area networks (LANs) are quantified. To that end a detailed comparison of the basic topologies and access couplers is provided in terms of amount of fiber required, average propagation delay, fault tolerance, 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. The results indicate that for 100 node LAN interconnection, the star topology requires 3.8 times as much fiber as a dual ring. 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. The maximum bit rate, assuming simple direct detection, is calculated for a fiber network based on the topology and type of access coupler. The results show that the more fault tolerant an access coupler is, the lower is the maximum bit rate it can support