Software-defined networking offers several benefits for networking by separating the control plane from the data plane. However, networks’ scalability, reliability, and availability remain as a big issue. Accordingly, multicontroller architectures are important for SDN-enabled networks. This paper gives a comprehensive overview of SDN multicontroller architectures. It presents SDN and its main instantiation OpenFlow. Then, it explains in detail the differences between multiple types of multicontroller architectures, like the distribution method and the communication system. Furthermore, it provides already implemented and under research examples of multicontroller architectures by describing their design, their communication process, and their performance results.

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We propose a particular class of transition probability matrices for discrete-time Markov chains with a closed form to compute the stationary distribution+ The stochastic monotonicity properties of this class are established+ We give algorithms to construct monotone, bounding matrices belonging to the proposed class for the variability orders+ The accuracy of bounds with respect to the underlying matrix structure is discussed through an example+

Software Defined Networking (SDN) has gained significant attention from network researchers and industry in recent years. Indeed, the SDN concept provides many advantages such as programmability and easy management of the network. However, it generates new challenges as scalability and performances issues, understanding in-depth the performances and limitations of the SDN concept is a prerequisite to its implementation and deployment in real networks. In this paper, we aim to present in a comprehensive way, the most important works that focus on performances of SDN. As SDN separates the control plane from the data plane, we first present research efforts made to enhance the performances of data plane devices, then, we give an overview of different solutions proposed to improve controller performances. We provide also an overview on recent control plane architectures with multiple controllers that have been proposed to meet performances and scalability constraints. Finally, we present the different techniques and tools used in literature to evaluate the performances of software defined networks. I.