Pairing SDN with network virtualization: The network hypervisor placement problem

A network virtualization hypervisor for Software Defined Networking (SDN) is the essential component for the realization of virtual SDN networks (vSDNs). Virtualizing software defined networks enables tenants to bring their own SDN controllers in order to individually program the network control of their virtual SDN networks. A hypervisor acts as an intermediate layer between the tenant SDN controllers and their respective virtual SDN networks. The hypervisor consists of the network functions that are necessary for virtualization, e.g., translation or isolation functions. For scalability, the hypervisor can be realized via multiple physically distributed instances each hosting the needed virtualization functions. In this way, the physical locations of the instances, which realize the hypervisor, may impact the overall performance of the virtual SDN networks. Network virtualization adds new dimensions to the general SDN controller placement problem. This paper initiates the study of the network hypervisor placement problem (HPP). The HPP targets the following questions: How many hypervisor instances are needed? Where should the hypervisor instances be placed in the network? For our study of the HPP, we provide a mathematical model that solves the HPP for a case where node and link capacity constraints are not considered. We propose four latency metrics for optimizing placement solutions based on our model for vSDNs. Covering a real network topology, our evaluation quantifies the trade-offs between the new metrics when used as objectives. Furthermore, we analyze the impact of the physical network topology on the optimization results and identify potentials for improvement, e.g., in terms of runtime.