Master Thesis - 2007

In recent years, the Internet traffic has been growing so fast due to its rapid development. Although the current IP routing, based on the shortest path algorithm, has shown its scalability in the Internet, the shortest path is not always the optimal path.

Overlay network, which is a logical network constructed over an underlying IP network, is a promising approach to overcome this problem. Overlay routing is a routing method based on overlay network in which end-to-end route selection can often find better alternative paths by relaying traffic among overlay nodes. Using overlay routing can enhance the reliability and performance of IP networks. When several overlay networks are constructed over the same underlying IP network, overlay paths on different overlay networks may share some links on the IP network. In general, however, because overlay networks do not realize the existence of other ones, they have no consideration on such shared physical links. Shared physical links, therefore, cannot be used effectively, which may lead to a decline in overlay routing performance.

In this thesis, a cooperative routing method for multiple overlay networks is proposed to overcome this problem and to improve the throughput of all overlay networks. This proposed routing method measures the end-to-end achievable bandwidth to evaluate overlay paths. When there are some overlay flows sharing the same physical link, a newly arriving flow may decrease the achievable bandwidth of other flows because some part of bandwidth is given to the new one. Focusing on this fact, I consider the decrease of achievable bandwidth as the influence among overlay networks, and use agent technology to measure it. The route whose sum of the achievable bandwidth and decrease of achievable bandwidth in other overlays is minimum is selected as the most appropriate path for the new flow.

The excellent performance of the proposed method has been evaluated by simulation experiments.