Virtualized control plane placement problem: Provisioning the control paths and architectures

Abstract

A fundamental problem to be resolved to achieve carrier grade functioning of an SDN network is the controller placement problem. The problem has been traditionally limited to optimally assigning switches to static physical controllers and placing those controllers over a network topology. However, virtualized controllers in place of physical ones could largely increase the dynamism in network control. In such a scenario, provisioning the requirements of the controllers themselves as virtual entities is also important. The virtual controllers may be inter-connected to each other via virtual controller-controller links and require additional virtualized support functions such as databases, to form a complete distributed virtual control plane. In this paper, we refer to the virtual control plane as the virtual control graph. This virtual control graph needs to be provisioned in addition to the traditional assignment of switches to controllers. Furthermore, all previous work assumes the control link between the switches and the controllers that control them can be created irrespective of the location of those controllers. This is untrue in a virtualized environment where the virtual control graph would connect to as well as control the very network they are provisioned on, using in band control channels. This switch to controller path must explicitly be provisioned in band and controller placement mechanisms must take into account the requirements of such provisioning algorithm as well. This paper proposes an extensible ILP model which addresses these two problems to enable the provisioning of virtual control graphs while also addressing the traditional requirements of controller placement. We then validate the proposed model with extensive simulations. The evaluation results show that this model can help address our considerations and can be applied to real world virtual controller graph placement scenarios.