On the Formation of Multi-Layer Hierarchies

Abstract

The application of hierarchy in large and dynamic networks improves scalability, survivability and robustness ofthese networks. Protocol designers have thus introduced mechanisms to automatically create and maintain hierarchical network structures. Existing work, however, is limited toforming only 2-layer structures, even though more than two layers are becoming increasingly necessary for larger networks. Furthermore, the majority of approaches focus on providing robustness in dynamic environments, and largely ignore the quality of the hierarchy formed. Such a design philosophy may result in hierarchy that actually degrades network performance. In this paper we present a general framework for the formation of multilayer hierarchies subject to network performance and hierarchy design requirements. We show the benefits of multilayer hierarchy in the automatic creation of more than two level routing domains. Furthermore, we show that our hierarchy framework can generate very good multilayer routing hierarchies that can minimize routing overhead. INTRODUCTION The application of hierarchical structures has many advantages on the network performance, survivability and robustness [3]. These benefits are most evident in large and dynamic network scenarios. In such scenarios the application of hierarchy results in improved manageability of the network and in more effective application of networking protocols (e.g. routing, security) since the network appears to be less dynamic and smaller in size, increasing the chances of the survivability and efficient application of these protocols. On the other hand the formation of hierarchical structures is not straightforward and may have opposite effects on the network performance from those expected. Specifically, a carelessly designed hierarchy can degrade the network performance significantly instead of improving it, since the hierarchy