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Statistical
Bandwidth Sharing: A Study of Congestion at Flow Level
S. Ben Fredj, T. Bonald, A. Proutiere, G. Regnie, J. Roberts
(France Telecom)
In this paper
we study the statistics of the realized throughput of elastic document
transfers, accounting for the way network bandwidth is shared dynamically
between the randomly varying number of concurrent flows. We first
discuss the way TCP realizes statistical bandwidth sharing, illustrating
essential properties by means of packet level simulations. Mathematical
flow level models based on the theory of stochastic networks are
then proposed to explain the observed behavior. A notable result
is that first order performance (e.g., mean throughput) is insensitive
with respect both to the flow size distribution and the flow arrival
process, as long as ``sessions'' arrive according to a Poisson process.
Perceived performance is shown to depend most significantly on whether
demand at flow level is less than or greater than available capacity.
The models provide a key to understanding the effectiveness of techniques
for congestion management and service differentiation.
     
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