We discuss the relevance of fairness as a design objective for congestion
control mechanisms in the Internet. Specifically, we consider a backbone
network shared by a dynamic number of short-lived flows, and study the
impact of bandwidth sharing on network performance. In particular,
we prove that for a broad class of fair bandwidth allocations,
the total number of flows in progress remains finite if the load of
every link is less than one. We also show that provided the bandwidth
allocation is ``sufficiently'' fair, performance is optimal
in the sense that the throughput of the flows is mainly determined
by their access rate. Neither property is guaranteed with unfair
bandwidth allocations, when priority is given to one class of flow
with respect to another. This suggests current proposals for a
differentiated services Internet may lead to suboptimal utilization
of network resources.
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