Distributed cost-based update policies for QoS routing on hierarchical networks

As the number of nodes of the Internet increasing, there are two main issues, scalable and the accuracy of routing information, have to be addressed for the reason of efficient routing. One of good solutions for the first issue is to form the flat networks into a hierarchy. In second issue, most of networks exchange the state information periodically which is referredto as a time-based update policy. The dynamic nature of network status makes it very difficult to set an appropriate update interval. Therefore, we first propose a distributed costbased update policy, referred to as the dynamic costbased update policy (DCU), to improve the accuracy of aggregated state information, while reducing the frequency of aggregation and information distribution. But, DCU may suffer from routing oscillation. We then propose another three update policies to avoid oscillation, which are extended from DCU, referred to as the DCU update with hysteresis policy (DCUH), the DCU update with cost threshold policy (DCUCT), and the DCU update with cost threshold and hold down timer policy (DCUCTT). Our simulation results indicate that the four proposed dynamic cost-based update policies yield less revenue loss and aggregation overhead; furthermore, the proposed DCUCTT policy yields the best performance while significantly reduces the overhead of aggregation and advertising of state information.