  FAST-TCP achieves better performance than traditional TCP-Reno schemes, but
unfortunately it is inherently unfair to older connections due to wrong
estimations of the round-trip propagation delay.
  This paper presents a model for this anomalous behavior of FAST flows, known
as the persistent congestion problem. We first develop an elementary analysis
for a scenario with just two flows, and then build up the general case with an
arbitrary number of flows. The model correctly quantifies how much unfairness
shows up among the different connections, confirming experimental observations
made by several previous studies.
  We built on this model to develop an algorithm to obtain a good estimate of
the propagation delay for FAST-TCP that enables to achieve fairness between
aged and new connections while preserving the high throughput and low buffer
occupancy of the original protocol. Furthermore, our proposal only requires a
modification of the sender host, avoiding the need to upgrade the intermediate
routers in any way.
