Workshop on
Mathematical Modeling and Analysis of Computer Networks
"BandwidthSharing Networks in Overload"
Sem Borst
AlcatelLucent Bell Labs & Eindhoven University of Technology
Bandwidthsharing networks as considered by Massoulie & Roberts provide
a natural modeling framework for describing the dynamic flowlevel
interaction among elastic data transfers.
Under mild assumptions, it has been established that a wide family of
socalled alphafair bandwidthsharing strategies achieve stability
in such networks provided that no individual link is overloaded.
In the talk we focus on alphafair bandwidthsharing networks
where the load on one or several of the links exceeds the capacity.
In order to characterize the overload behavior, we examine the fluid
limit, which emerges from a suitably scaled version of the number of
flows of the various classes.
The convergence of the scaled number of flows to the fluid limit is
empirically validated through simulation experiments.
We prove that the fluid limit is a linear function of time, and derive
a fixedpoint equation for the corresponding asymptotic growth rates.
It is further shown that the fixedpoint solution is also a solution
to a related strictly concave optimization problem, and hence unique.
We use the fixedpoint equation to investigate the impact of the
traffic intensities and the variability of the flow sizes on the
asymptotic growth rates.
The results are illustrated for linear topologies and star networks
as two important special cases.
Finally, we briefly discuss extensions to models with user impatience.
Note: +Based on joint work with Regina Egorova (CWI & Eindhoven
University of Technology) and Bert Zwart (Georgia Tech)
