Preventive Start-Time Optimization of OSPF Link Weights against Link Failure for Hose Model

Optimizing link weights in an OSPF network is a key traffic engineering problem to reduce the network congestion. Previous studies introduced three policies on link weigth optimization, which are called Start-time Optimization (SO), Runtime Optimization (RO), and Preventive Start-time Optimization. All of them were used to be applied to a pipe mode, in which a traffic matrix, representing the traffic demand between each source and destination node pair, is exactly known. In practical, it is difficult for a network operator to measure or specify an exact traffic matrix. On the other hand, it is easy for a network operator to specify a hose model, in which only the total amount of traffic each node injects into the network and the total amount of traffic each node receives from the network, has to be known. This paper proposes a preventive start-time optimization scheme for the hose model. It employs a heuristic algorithm to determine an optimal set of link weights to minimize the worst-case congestion ratio for any single link failure. A straight-forward method to find an optimal set of link weights is to search the link weight space against all the possible traffic matrices and topologies created by link failure. Obviously, this approach needs a huge amount of computation time. The proposed scheme effectively selects the worst-case performance traffic matrix and tries to reduce the worst-case congestion ratio. Numerical results via simulations show that the proposed scheme effectively reduces the worst-case congestion ratio compared to SO.