Master and Slave Controller Assignment Model Against Multiple Failures in Software Defined Network

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This paper proposes a master and slave controller assignment model against multiple controller failures in software defined network with considering propagation latency between switches and controllers. In our model, a controller can be assigned to multiple switches, and the survivability of each switch is guaranteed to a certain degree by assigning multiple controllers to it. We define the average-case expected propagation latency, the worst-case expected propagation latency, and the expected number of switches within a propagation latency bound, as three different objectives to be optimized, which lead to three different problems, in this paper. We formulate the proposed master and slave controller assignment model with different goals as three mixed integer linear programming problems. Results show that the optimal assignments vary for different problems. A greedy algorithm with polynomial time complexity is introduced to solve the same optimization problems. We evaluate the performance of introduced greedy algorithm compared with the optimal value in one of the problems, which minimizes the average-case propagation latency. The numerical results reveal that the computational time of running the greedy algorithm to obtain a solution is about 10<sup>−3</sup> times compared to that of solving the mixed integer linear programming problem; the obtained objective value is about 1.00324 times of the optimal value in average in our examined scenarios.