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Network Instrumentation for End-to-End Measurements

An important consideration when deploying realtime applications such as IP Telephony is how to ensure that the network delivers the stringent QoS requirements of these applications. Prior to deployment, assessing whether an enterprise network can handle IP Telephony ensures a successful deployment. A network assessment approach recently introduced in the ExpertNetTM tool suite involves distributing small measurement devices in the network. These devices inject synthetic RTP traffic and collect end-to-end measurements that represent end-to-end call quality. In this approach, the placement of measurement devices impacts the network coverage and accuracy of the analysis. In this paper, we address the problem of how to place such measurement devices in a network to ensure a comprehensive analysis. Specifically, we focus on two issues: first where to place network measurement devices when the network topology is known and second how to estimate the number of such devices in the absence of network topology information. In this paper, we address the first problem by providing two heuristic algorithms for placing measurement devices in a given network. We evaluate these heuristics using synthetic networks. We address the second problem by proposing a technique to estimate the number of measurement devices using the size of a network. To evaluate the performance of our technique, we conducted a study on actual enterprise network topologies. Using our technique, we predicted the number of endpoints based on network size and compared these figures to the number of endpoints placed by the proposed algorithms using the network topology. Our results indicate that the predictions are comparable to the number of endpoints placed using the actual enterprise network topology.