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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

Citation key | C-NCDBQNES-07 |
---|---|

Author | Ciucu, Florin |

Title of Book | Managing Traffic Performance in Converged Networks (Proceedings of the 20th International Teletraffic Congress (ITC 20)) |

Pages | 495-506 |

Year | 2007 |

ISBN | 978-3-540-72989-1 |

ISSN | 0302-9743 |

Online ISSN | 1611-3349 |

DOI | http://dx.doi.org/10.1007/978-3-540-72990-7_45 |

Location | Ottawa, Canada |

Address | Berlin / Heidelberg, Germany |

Volume | 4516 |

Month | June |

Publisher | Springer |

Series | Lecture Notes in Computer Science |

Abstract | The purpose of this paper is to shed light on the accuracy of probabilistic delay bounds obtained with network calculus. In particular, by comparing calculus bounds with exact results in a series of M/M/1 queues with cross traffic, we show that reasonably accurate bounds are achieved when the percentage of cross traffic is low. We use recent results in network calculus and, in addition, propose novel bounds based on Doob’s maximal inequality for supermartingales. In the case of single M/M/1 and M/D/1 queues, our results improve existing bounds by Ω((log(1-ρ)^(-1))/(1-ρ)) when the utilization factor ρ converges to one. |