Modelling TCP throughput and fairness

Since TCP traffic is elastic, a fundamental issue is the behaviour of multiple TCP flows competing for bandwidth on a shared link. Motivated by the ubiquity of drop-tail queueing in current networks, our focus in this paper is on developing analytic models suited to characterising the throughput and fairness of competing TCP flows in drop-tail environments. Building on recent ideas from the theory of positive linear systems, we obtain simple, insightful closed-form expressions for throughput and fairness. The accuracy of these expressions is confirmed in extensive simulations across a range of network conditions. In particular, they are found to provide accurate estimate of mean fairness and throughput even when flows are not synchronised.