  The MGT fluid model has been used extensively to guide designs of AQM schemes
aiming to alleviate adverse effects of Internet congestion. In this paper, we
provide a new analysis of a TCP/AQM system that aims to improve the accuracy of
the MGT fluid model especially in heavy traffic conditions. The analysis is
based on the consideration of two extreme congestion scenarios that leads to
the derivation of upper and lower bounds for the queue length and marking
probability dynamics and showing that they approach each other in steady state.
Both discrete and continuous time models are provided. Simulation results
demonstrate that the new model achieves a significantly higher level of
accuracy than a simplified version of the MGT fluid model.
