Control and recovery from rare congestion events in a large multi-server system |
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Authors: | Duffield NG Whitt W |
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Institution: | (1) AT&T Laboratories, Room {A175, A117}, 180 Park Avenue, Florham Park, NJ 07932-0971, USA |
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Abstract: | We develop deterministic fluid approximations to describe the recovery from rare congestion events in a large multi-server
system in which customer holding times have a general distribution. There are two cases, depending on whether or not we exploit
the age distribution (the distribution of elapsed holding times of customers in service). If we do not exploit the age distribution,
then the rare congestion event is a large number of customers present. If we do exploit the age distribution, then the rare
event is an unusual age distribution, possibly accompanied by a large number of customers present. As an approximation, we
represent the large multi-server system as an M/G/∞ model. We prove that, under regularity conditions, the fluid approximations are asymptotically correct as the arrival rate
increases. The fluid approximations show the impact upon the recovery time of the holding-time distribution beyond its mean.
The recovery time may or not be affected by the holding-time distribution having a long tail, depending on the precise definition
of recovery. The fluid approximations can be used to analyze various overload control schemes, such as reducing the arrival
rate or interrupting services in progress. We also establish large deviations principles to show that the two kinds of rare
events have the same exponentially small order. We give numerical examples showing the effect of the holding-time distribution
and the age distribution, focusing especially on the consequences of long-tail distributions.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | multi-server systems high congestion recovery from congestion overload control long-tail distributions transient behavior fluid limits fluid approximations large deviations Sanov's theorem residual lifetimes age distributions |
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