Integer programming model and exact solution for concentrator location problem

Topological design of centralized computer networks is an important problem that has been investigated by many researchers. Such networks typically involve a large number of terminals connected to concentrators, that are then connected to a central computing site. This paper focuses on the concentrator location problem among general topological network design problems. The concentrator location problem is defined as determining the following: (i) the number and locations of concentrators that are to be open, and (ii) the allocation of terminals to concentrator sites without violating the capacities of concentrators. An exact algorithm (fractional cutting plane algorithm/branch-and-bound) is proposed for solving this problem. In this approach an integer programming problem is formulated. Then a class of valid inequalities is derived and a greedy algorithm for a separation problem is shown. A good lower bound is obtained by a lifting procedure. We show how to implement the algorithm using a commercial software for LP and branch-and-bound. Finally, the computational efficiency of our algorithm is demonstrated.