A comparison of workload models of the capacity available for sharing among privately owned workstations

The author studies four models of the distributions of the periods in which idle workstation capacity is available for sharing and the distributions in which capacity cannot be shared. One model is derived from traces of user activity on workstations. The remaining three models are constructed in the form of stochastic processes. Each model as a stochastic process differs in complexity and the degree of accuracy which it captures the characteristics of the traces. An exponential distribution is the simplest model used to describe the length of periods which capacity is available and unavailable for sharing. A model of increased complexity uses hyperexponential distributions, while the most complex model has a separate hyperexponential distribution for each workstation. Although an increasing degree of complexity in a model can more accurately represent the patterns of activity on workstations, a hyperexponential distribution is shown to capture important characteristics significantly beyond an exponential distribution without requiring the amount of detail needed for specifying separate distributions for each workstation