Local Unicast Routing Control Agent

Routing for link state routing protocols such as OSPF is determined by computing shortest-paths on the network topology graph. In conventional routing the OSPF link costs are configured a-priori before the network is deployed, and remain fixed until manually changed. If subsequently, link quality degrades or alternate links become available, routing paths may become sub-optimal in terms of throughput or end to end delay. In this paper we describe a distributed routing optimization technology called local unicast routing control agent (L-URCA). L-URCA is co-located with every router, and dynamically updates the OSPF link costs to re-route traffic away from congested or highly utilized links. L-URCA only uses local information, i.e. information that can be gathered from the local router. This removes the overhead of messaging and state synchronization between L-URCA processes. One simple heuristic for local-rerouting is to dynamically set the link cost proportional to link utilization. This tends to re-route traffic away from the congested link, however it can lead to congestion elsewhere in the network and oscillation of traffic. The heuristics of L-URCA are specifically designed to set the OSPF weights such that traffic following the shortest-path will approximately minimize the average delay experienced in the network. The heuristics proposed for L-URCA are based on robust optimization techniques that take into account uncertainties of traffic, capacity and routing decisions in other parts of the network. Examples and further steps in this ongoing research project are briefly discussed.