### Inhalt des Dokuments

# 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

Ciucu, Florin and Hohlfeld, Oliver and Chen, Lydia Y. (2011). On the Convergence to Fairness in Overloaded FIFO Systems. *Proceedings of the 30th IEEE International Conference on Computer Communications (INFOCOM '11)*. IEEE, 1988–1996.

Ciucu, Florin and Schmitt, Jens and Wang, Hao (2011). On Expressing Networks with Flow Transformations in Convolution-Form. *Proceedings of the 30th IEEE International Conference on Computer Communications (INFOCOM '11)*. IEEE, 1979–1987.

Burchard, Almut and Liebeherr, Jörg and Ciucu, Florin (2011). On Superlinear Scaling of Network Delays. *IEEE/ACM Transactions on Networking (ToN)*, 1043–1056.

Ciucu, Florin and Hohlfeld, Oliver (2010). On Computing Bounds on Average Backlogs and Delays with Network Calculus. *Proceedings of IEEE International Conference on Communications (ICC '10)*. IEEE, 1–5.

Liebeherr, Jörg and Burchard, Almut and Ciucu, Florin (2010). Non-asymptotic Delay Bounds for Networks with Heavy-Tailed Traffic. *Proceedings of IEEE INFOCOM '10*. IEEE, 1–9.

Ciucu, Florin (2009). End-to-End Delay Analysis for Networks with Partial Assumptions of Statistical Independence. *4th International Conference on Performance Evaluation Methodologies and Tools (VALUETOOLS 2009)*

Ciucu, Florin and Liebeherr, Jörg (2009). A Case for Decomposition of FIFO Networks. *INFOCOM 2009. The 28th Conference on Computer Communications.*. IEEE Computer Society, 1071–1079.

Ciucu, Florin (2007). Network Calculus Delay Bounds in Queueing Networks with Exact Solutions. *Managing Traffic Performance in Converged Networks (Proceedings of the 20th International Teletraffic Congress (ITC 20))*. Springer, 495-506.

Burchard, Almut and Liebeherr, Jorg and Ciucu, Florin (2007). On Ω(HlogH) Scaling of Network Delays. *Proceedings of IEEE INFOCOM 2007*. IEEE, 1866–1874.

Ciucu, Florin (2007). Exponential Supermartingales for Evaluating End-to-End Backlog Bounds. *Performance Evaluation Review*. ACM, 21–23.

Ciucu, Florin and Burchard, Almut and Liebeherr, Jorg (2006). Scaling Properties of Statistical End-to-End Bounds in Network Calculus. *IEEE Transactions on Information Theory*. IEEE Press, 2300–2312.

Ciucu, Florin and Burchard, Almut and Liebeherr, Jorg (2005). A Network Service Curve Approach for the Stochastic Analysis of Networks. *Proceedings of ACM SIGMETRICS 2005*. ACM, 279–290.