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This paper develops a simple and accurate stochastic model for the steady-state throughput of a TCP NewReno bulk data transfer as a function of round-trip time and loss behavior. Our model builds upon extensive prior work on TCP Reno throughput models but differs from these prior works in three key aspects. First, our model introduces an analytical characterization of the TCP NewReno fast recovery algorithm. Second, our model incorporates an accurate formulation of NewReno's timeout behavior. Third, our model is formulated using a flexible two-parameter loss model that can better represent the diverse packet loss scenarios encountered by TCP on the Internet. We validated our model by conducting a large number of simulations using the ns-2 simulator and by conducting emulation and Internet experiments using a NewReno implementation in the BSD TCP/IP protocol stack. The main findings from the experiments are: 1) the proposed model accurately predicts the steady-state throughput for TCP NewReno bulk data transfers under a wide range of network conditions; 2) TCP NewReno significantly outperforms TCP Reno in many of the scenarios considered; and 3) using existing TCP Reno models to estimate TCP NewReno throughput may introduce significant errors.