The Overload Performance of Engineered Networks With Nonhierarchical and Hierarchical Routing

Abstract

We report the results of a study of the performance of engineered nonhierarchical and hierarchical routing networks under overloads. This study was motivated by results obtained from mathematical models for small, symmetric, uniformly loaded, nonhierarchical networks with transparent switching systems, showing the existence of network instabilities. We extend the mathematical models to more general nonhierarchical networks, and show with analysis and an extant simulation model that such instabilities are also found in nonsymmetric, nonhierarchical networks. We then use our models to consider whether engineered nonhierarchical networks exhibit such unstable behavior. No instabilities are found in the engineered nonhierarchical networks considered here. However, the nonhierarchical networks consistently demonstrate a drop in carried load between 10- and 15-percent overloads. Our analysis of comparably engineered hierarchical networks shows that these networks do not exhibit a drop in carried load under overloads (in the absence of switching system dynamics). Finally, we show that using trunk reservation for first-routed traffic allows the formulation of a control strategy that provides a high level of network carried load during overloads.