As the Internet has grown in size and diversity of applications, two trends have emerged to provide good end-user perceived performance. First, servers are often replicated for better scalability of the service. Second, QoS approaches, such as the differentiated services framework, have been proposed as enhancement to the best-effort IP service. Re are interested in the combination of these two trends; that is, replicated servers in QoS-based networks. In this paper, we focus on the problem of selecting amongst replicated servers in the context of differentiated service networks. Our contributions are twofold. First, we design a QoS-based server selection architecture. The architecture Ls scalable in the sense that server selection and resource reservation are done in an aggregated fashion and operate in the background, rather than being driven by individual client demand. At the same time, the architecture offers fast response time to client requests for server selection. Second, we explore the design space implied by the architecture and evaluate various design options including signalling protocols, server selection/sorting algorithms and resource reservation granularity.
