A comparison of two methods for advancing time in parallel discrete event simulation

We compare the design and implementation of a parallel simulation of a traffic flow network using two different approaches: event-driven and time-driven. Our experiments with the sequential implementation of the two approaches correlates with previous research (Nance, 1971). We design a conservative parallel implementation of the traffic flow problem where we obtain a maximum speedup of 9.27 using 16 Sun workstations running under parallel virtual machine or PVM (Geist et al., 1993). We use wall-clock time as a measure of execution speed. We show that appreciable speedup can be achieved in parallelizing either the event-driven or time-driven approach. We also show that speedup is a misleading metric when used to compare the parallelizability of the two approaches. Parallel performance, as measured by speedup, may be better when the sequential performance is poor. For example, the time-driven implementation achieved better speedup than the event-driven implementation for few cars in the system; however the sequential time-driven implementation required longer to execute than the event-driven implementation for few cars in the system. Similarly for many cars in the system, the event-driven implementation achieved better speedup than the time-driven implementation