Quand: Le 1er décembre 2017, à 10h45
Où: Salle C305 à Télécom SudParis, à Evry

Part I « Performance modelling of transmissions in very large network topologies »

Transient state queueing models help us to understand better the dynamics of internet transmissions and the performance of traffic control algorithms. Fluid flow approximation, due its simplicity, as it is based on first-order differential equations, is popular and frequently used — but even it, if applied to large topologies, is time and space consuming. Its algorithm is based on
iterative calculations on large mutually interdependent structures. In consequence, the bottleneck of the method lies not in numerical computations but in storing and selection of data. This is why we investigate an approach in which a database (SAP HANA) and its language are used to implement the method. The model logic is represented by ETL (Extract, Transform and Load) customizable and user-friendly processes. The numerical examples are based on a real topology having over 100 000 nodes.

Part II: « A queueing model of an insurance database interactive system, comparison of modelling methods »

We present a queueing model of a computer network which is installed at a branch of the largest Polish insurance company. The network is used to store and use documents related to company clients. Our model concentrates on the database server and applications used to retrieve and modify the documents. The model is based on measurements gathered in this system. The goal is twofold: (i) elaborate a tool that is able to predict the performance of the system in case of modifications (more terminals, more servers) (ii) compare the usefulness of several methods (discrete event simulation, Markov chains, Mean Value Analysis and diffusion approximation) implemented in this real-case study.

Biographie

Tadeusz Czachórski is a professor at the Silesian University of Technology and the director of the Institute of Theoretical and Applied Informatics of Polish Academy of Sciences, IITiS PAN, Gliwice. He spent more than five years at several French universities and research institutes (IRISA Rennes, PRISM University of Versailles, ISEM Orsay Paris-Sud, INT Evry, LIPN Paris-Nord, LACL Paris Est, IBISC Univeriste d’Evry) and still maintains scientific cooperation with some of these centres. Since 1990 he is a member of the Committee of Informatics of Polish Academy of Sciences, currently head of the section of computer networks and distributed systems of the committee, chair of IFIP Technical Committee TC5 « Information Technology and Applications ». His scientific interests include mathematical methods and software related to modelling and performance evaluation of wide area computer networks, especially the Internet.