A fast-convergence scheme to update metrics without loop in OSPF networks

This paper proposes a fast-convergence scheme to update metrics avoiding loop in Open Shortest Path Fast (OSPF) networks. In original OSPF networks, when metrics are updated to improve the routing performance, packets may be routed in a loop in transient states. This may cause packet loss and inefficiency in network resources. To avoid transient loops, a conventional scheme gives each router its priority, which is called a rank, in terms of time to update metrics. However, when the updated metrics include both larger and smaller values than the ones before the update, two updating processes, each of which corresponds either larger or smaller values, are required. It takes time to converge to update all the metrics in the conventional scheme. The proposed scheme tries to transform a set of the updated metrics into another equivalent set of metrics that are equal to or either larger or smaller values than the ones before the update, while the targeted routes in the proposed scheme are exactly the same as those of the conventional scheme. This requires only one updating process. Numerical results indicate that the proposed scheme reduces the convergence time with 24.7% in average in our examined networks, compared with that of the conventional scheme.