On optimal hierarchical SDN

To address scalability concerns, hierarchical control plane organization has been proposed for SDN. However, an open question is how such a hierarchy should look like. In this paper, we model the impact of hierarchies on control plane performance and derive an expression for an optimal hierarchical organization for a given network scale. We then show that using a 4-layer SDN is sufficient for practical network scales, suggesting feasibility and relevance of this approach. Finally, we illustrate the elasticity of hierarchical SDN, which enables a more flexible cost evolution of the SDN control plane.