1. Department of Networked Systems and Services, Budapest University of Technology and Economics, Magyar tudósok körútja 2, Budapest, Hungary
2. Faculty of Informatics and Mathematics, University of Passau, Innstraße 43, 94032 Passau, Germany
3. Faculty of Informatics, University of Debrecen, Egyetem tér 1, P.O. Box 12, 4010 Debrecen, Hungary