J. W. Wong’s research while affiliated with University of Waterloo and other places

Simulation, particularly of networks of queues, is an application with a high degree of inherent parallelism, and is of considerable practical interest. We continue the analysis of synchronization methods for distributed simulation, defined by the taxonomy in our previous paper. Specifically, we develop algorithms for time-driven simulation using a network of processors. For most of the synchronization methods considered, each node k of an n-node network simulation cannot proceed directly with its part of a simulation. Rather, it must compute some function Bk(ν1, ν2, …, νn), where νi is some value which must be obtained from node i. The value of νi at each node changes as the simulation progresses, and must be broadcast to every other node for the recomputation of the B-functions. In some cases, it is advantageous to compute the B-function in a distributed manner. Broadcast algorithms for such distributed computation are presented. Since the performance of a broadcast algorithm depends on the properties of the inter-process communication facility, we characterize some particular cases and give algorithms for each of them.

Simulation, particulary of networks of queues, is an application with a high degree of inherent parallelism and is of great practical interest. We hope to exploit this parallelism by performing simulations using a network of cheap, but slow, micro-processors.We define a taxonomy by which we classify a number of parameters of a distributed simulation method, and seek solutions to problems of synchronization, deadlock prevention and inter-process communication arising with various methods in each class of the taxonomy. We concentrate in particular on the class (loose, event-driven) which seems to possess the greatest potential parallelism, and on the class (scaled, tight, time-driven) which allows mock-up studies of real systems. We give algorithms for deadlock prevention and detection, and briefly discuss the design of a distributed operating system to support the simulation application.This research forms part of a joint program with the Dept. of Computer Sciences, University of Texas at Austin, directed by Prof. K.M. Chandy.

Discrete simulation is a widely used technique for system performance evaluation. The conventional approach to discrete simulation (e.g., GPSS, Simscript) does not attempt to exploit the parallelism typically available in queueing network models. In this paper, a distributed approach to discrete simulation is presented. It involves the decomposition of a simulation into components and the synchronization of these components by message passing. This approach can result in the speedup of the total time to complete a given simulation if a network of processors is available. The architecture of a microcomputer network suitable for distributed simulation is described and some results concerning the distributed approach are presented.

An open queueing network model is used to derive the distribution of end-to-end delay in a message-switched network. It is shown that under fixed routing, the end-to-end delay of messages belonging to a particular source-destination node pair is given by a sum of independent and exponentially distributed random variables. The generalization of this basic result to random routing and to messages belonging to a group of a source-destination pairs is also considered. Numerical examples based on a hypothetical network are presented.