Christos N. Houmkozlis is currently in the Department of Electrical and Computer Engineering at Aristotle University of Thessaloniki. His research interests include nonlinear systems, robust adaptive control, modeling and control of communications networks, control over heterogeneous networks, resource management, and pricing in networks. George A. Rovithakis is Associate Professor in the Department of Electrical and Computer Engineering at Aristotle University of Thessaloniki. His research interests include nonlinear robust adaptive control, neural networks for identification, control of uncertain systems, and control issues arising in computer networks.