A traffic-handling comparison of centralized and distributed ATM switching systems

This paper describes a geographically distributed ATM switching architecture that exploits new possibilities offered by lightwave technology. Small modules that provide both an access and an ATM switching function are distributed over some extended geographical area and connected to a passive optical medium. Each module is equipped with some small number of electrooptic transmitters and receivers that provide access to the medium. Assignment of wavelengths to transmitter/receiver pairs create logical channels that are wavelength-multiplexed onto the medium, thus creating a logical connection diagram among the modules. Advantages of the lightwave-based distributed architecture are the huge bandwidth of the medium, a high degree of modularity to facilitate growth, high reliability, and the ability to provide “clear channels” among modules. On the other hand, if the externally offered flow of ATM cells among modules is too uniform, then each module may be capable of supporting only a fraction of the load that could be carried by any port of a fully connected centralized ATM switch with output queueing. Fortunately, under the much more realistic assumption of nonuniform traffic, the independence between the logical connection diagram and the physical topology of the medium can be exploited by reconfiguring the connection diagram to “match” the nonuniformity of the cell traffic. Simulation results show that, as the nonuniformity becomes larger, the reconfiguration technique allows the traffic-handling capability of a distributed switch to match that of a centralized switch