Fluid Models of TCP-based Flows

Don Towsley
Department of Computer Science
University of Massachusetts
Amherst, MA 01003

In this talk we use fluid models to describe the behavior of the
Internet TCP transport protocol. We describe two approaches. Both are
concerned with predicting the performance of many TCP flows traversing
a network of routers. The first focusses on the use of fixed point methods
for obtaining estimates of TCP session throughput and packet loss rate,
router loss rate, and other measures. Comparison with simulation
demonstrates this to be quite accurate. The second approach
focusses on the transient behavior of a set of TCP flows
traversing a network. This is described through a simple set
of differential equations hat are easily solved numerically.
Preliminary comparisons to simulation show this to be a promising approach.
Furthermore, they can be used to shed light on the effectiveness of active
queue management policies such as RED (random early detect).

We conclude the talk with a number of open technical problems that we
have encountered during our work.

Joint work with T. Bu, W. Gong, and V. Misra.