The Implication of Network Performance on Service Quality
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As the Internet infrastructure evolves to include Quality of Service (QoS), it is necessary to map application quality requirements to the the network performance specifications in terms of delay and loss rate. While past work has addressed the dependency of audio and video applications on these underlying QoS metrics, little work has been done in the area of Web traffic. In this paper, we use a combination of emulation, simulation, and analysis to quantify the effect of network performance metrics on HTTP request latency and the perceptual quality of an audio application. Although our work is done in the context of a LAN environment, the results generalize to a more general WAN environment. Our contributions are three-fold. First, we combine simulation and emulation techniques in setting up an accurate yet controllable testbed. The use of network simulator Entrapid and its built-in Fast Ethernet Simulation makes our simulation both efficient and accurate. Second, for Web applications, we define a new TCP short connection model that computes the latency of Web retrieval accurately and efficiently given only packet delay and loss rate characteristics apriori. Experiments show that our model significantly improves the accuracy of the best-known TCP short connection model by correctly capturing TCP retransmission behavior. Finally, for Internet telephony, we show that the packet delay variance is the dominant network characteristics which affect the perceptual quality. As a result, the service quality drops dramatically when the Ethernet offered load reaches 80%. This can serve as a guideline for studies towards improving service quality of Internet telephony.