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Analytical Performance Evaluation

The success of computer and communication systems strongly depends on their performance, typically reflected in the perception of speed. Optimizing system performance, subject to a set of resource and cost constraints, is thus a critical design goal for system engineers. An elegant technique to help in this matter is performance evaluation which can be performed either by measurements, simulation, or using theoretical methods. In particular, analytical performance evaluation has the fundamental merit of rapidly leading to rigorous and unequivocal insight into the behavior of systems which can be accordingly tuned and optimized.

Our own research is concerned with extending the theory of the stochastic network calculus, which is a probabilistic extension of the deterministic network calculus conceived by R. Cruz in the early 1990's. Over the past two decades the calculus has established itself as a versatile alternative methodology to the classical queueing theory for the performance analysis of computer and communication networks. Its prospect is that it can deal with problems that are fundamentally hard for queueing theory, based on the fact that it works with bounds rather than striving for exact solutions. We are in particular concerned with various fundamental research problems related to modelling and analyzing networks with flow transformations, or improving the bounds accuracy using refined inequalities. On the long term, we believe that our research can significantly contribute to establishing the stochastic network calculus as an indispensable mathematical tool for the performance analysis of resource sharing based systems.

Selected Publications

A Case for Decomposition of FIFO Networks
Citation key CL-CDFN-09
Author Ciucu, Florin and Liebeherr, Jörg
Title of Book INFOCOM 2009. The 28th Conference on Computer Communications.
Pages 1071–1079
Year 2009
ISBN 978-1-4244-3512-8
ISSN 0743-166X
DOI http://dx.doi.org/10.1109/INFCOM.2009.5062019
Location Rio de Janeiro, Brazil
Month April
Publisher IEEE Computer Society
Abstract Recent findings showing that the output of traffic flows at packet switches has similar characteristics as the corresponding input enable a decomposition analysis of a network where nodes can be studied in isolation, thus simplifying an end- to-end analysis of networks. However, network decomposition results currently available are mostly many-sources asymptotics. In this paper we explore the viability of network decomposition in a non-asymptotic regime with a finite number of flows. For traffic with Exponentially Bounded Burstiness (EBB) we derive statistical bounds for the output traffic at a FIFO buffer and compare them with bounds on the input. By evaluating the accuracy of the output bounds with exact results available for special cases and by using numerical examples we find that conditions for network decomposition appear favorable even if the number of flows is relatively small.
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