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Empirical and Analytical Evaluation of Systems with Multiple Unreliable Servers

Lookup NU author(s): Dr Jennie Palmer, Emeritus Professor Isi Mitrani



We construct, analyze and solve models of systems where a number of servers offer services to an incoming stream of demands. Each server goes through alternating periods of being operative and inoperative. The objective is to evaluate and optimize performance and cost metrics. A large real-life data set containing information about server breakdowns is analyzed first. The results indicate that the durations of the operative periods are not distributed exponentially. However, hyperexponential distributions are found to be a good fit for the observed data. A model based on these distributions is then formulated, and is solved exactly using the method of spectral expansion. A simple approximation which is accurate for heavily loaded systems is also proposed. The results of a number of numerical experiments are reported.

Publication metadata

Author(s): Palmer J, Mitrani I

Publication type: Report

Publication status: Published

Series Title: School of Computing Science Technical Report Series

Year: 2005

Pages: 20

Print publication date: 01/12/2005

Source Publication Date: December 2005

Report Number: 936

Institution: School of Computing Science, University of Newcastle upon Tyne

Place Published: Newcastle upon Tyne