The price of evolution in incremental network design: The case of mesh networks

In practice most service-provider and enterprise networks are designed incrementally over time. This ongoing and heuristic design process is driven by changes in the underlying objectives and constraints (the “environment”). We first formulate the incremental network design approach as the constrained minimization of a certain modification cost, and compare that with the classical design approach in which the objective is to minimize the total network cost. We evaluate the cost overhead and the evolvability of incremental designs under two network expansion models (random and gradual), evaluating incrementally designed networks in terms of cost, performance (propagation delay) and robustness. Even though incremental design has some cost overhead, this overhead does not increase as the network grows. In the case of mesh networks, the incremental design process leads to networks with larger link density, lower average delay and improved robustness.