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Abstract
Application-layer overlay networks have recently emerged as a promising platform to deploy additional services over the Internet. A virtual network of overlay nodes can be used to regulate traffic flows of an underlay network, without modifying the underlay network infrastructure. As a result, an opportunity to redeem the inefficiency of IP routing and to improve end-to-end performance of the Internet has arisen, by routing traffic over multiple overlay paths. However, to achieve high end-to-end performance over the Internet by means of overlay networks, a number of challenging issues, including limited knowledge of the underlay network characteristics, fluctuations of overlay path performance, and interactions between overlay and the underlay traffic must be addressed. This thesis provides solutions to some of these issues, by proposing a framework to construct a multi-path overlay architecture for improving Internet end-to-end performance and availability. The framework is formed by posing a series of questions, including i) how to model and forecast overlay path performance characteristics; ii) how to route traffic optimally over multiple overlay paths; and iii) how to place overlay nodes to maximally leverage the Internet resource redundancy, while minimizing the deployment cost. To answer those research questions, analytical and experimental studies have been conducted. As a result, i) a loss model and a hybrid forecasting technique are proposed to capture, and subsequently predict end-to-end loss/delay behaviors; with this predictive capability, overlay agents can, for example, select overlay paths that potentially offer good performance and reliability; ii) to take full advantage of the predictive capability and the availability of multiple paths, a Markov Decision Process based multi-path traffic controller is developed, which can route traffic simultaneously over multiple overlay paths to optimize some performance measures, e.g. average loss rate and latency. As there can be multiple overlay controllers, competing for common resources by making selfish decisions, which could jeopardize performance of the networks, game theory is applied here to turn the competition into cooperation; as a consequence, the network performance is improved; iii) furthermore, to facilitate the deployment of the multi-path overlay architecture, a multi-objective genetic-based algorithm is introduced to place overlay nodes to attain a high level of overlay path diversity, while minimizing the number of overlay nodes to be deployed, and thus reducing the deployment cost. The findings of this thesis indicate that the use of multiple overlay paths can substantially improve end-to-end performance. They uncover the potential of multi-path application-layer overlay networks as an architecture for achieving high end-to-end performance and availability over the Internet.