In this paper, we outline a methodology that can be applied to model the behavior of TCP Reno flows. The proposed methodology stems from a Markovian model of a single TCP source, and eventually considers the superposition and interaction of several such sources using standard queueing analysis techniques. Our approach allows the evaluation of such performance indices as throughput, queueing delay and segment loss of TCP flows. The results obtained through our model are validated by means of simulation, under different traffic settings.