Connection Preemption in Multi-Class Networks

We address the problem of connection preemption in a multi-class network environment. Our objective is: i) to minimize the number of preempted connections, and ii) to minimize the total preempted bandwidth, in that order. We show that this problem is NP-complete by reducing it to a well-known NP complete problem - the subset sum problem. Therefore, a known polynomial time algorithm, such as Minn Conn (1), to solve this problem is suboptimal. We present an optimal algorithm with exponential complexity that can be used when the network load is light. We also present a fully polynomial time approximation algorithm that performs within a bounded factor from the optimal, and can be used in large networks having thousands of connections. We compare the performance of exact and approximate algorithms in a practical scenario by conducting simulations on a network representing twenty largest metros in the U.S. The simulations show that, on average, the approximate algorithm preempts bandwidth which is only a small fraction more as compared to that preempted by the exact algorithm, but is an order of magnitude more efficient in terms of execution time.