In this paper we develop a simple analytic characterization of the steady state throughput as a function of loss rate and RTT for a bulk transfer TCP flow, i.e., a flow with an unlimited amount of data to send. Unlike the models in [1,2], our model captures not only the behavior of TCP's fast retransmit mechanism (which is also considered in [1,2]) but also the effect of TCP's timeout mechanism on the congestion window. Our measurements suggest that this latter behavior is important from a modeling perspective, as almost all of our TCP traces contained more timeout events than fast retransmit events. Our measurements demonstrate that our model is able to more accurately predict TCP throughput and is accurate over a wider range of loss rates. [1] M. Mathis, J. Semske, J. Mahdavi and T. Ott, The Macroscopic Behavior of the TCP Congestion Avoidance Algorithm, Computer Communication Review, Vol 27, Number 3, July 1997. [2] T. Ott, J. Kemperman and M. Mathis, The Stationary Behavior of Ideal TCP Congestion Avoidance, in preprint. [3] J. Mahdavi and S. Floyd, TCP-Friendly Unicast Rate-Based Flow Control, Note sent to end2end-interest mailing list, January 1997.