+My appreciation and thanks go to the members of the team AND ({\it Algorithmique Numérique Distribuée}) for the warm and friendly atmosphere in which they allowed me to work. So thank you to Jacques Bahi, Pierre-Cyrille Héam, Huu Quan Do, Bassam Alkindy, Abdallah Makhoul, Huda Al-Nayyef, Jean-Claude Charr, Jean-François Couchot, Ahmed Mostefaoui, Ahmed Fanfakh, Yousra Ahmed Fadil, Stéphane Domas, Pierre Saenger, Zeinab Fawaz, Arnaud Giersch, Christophe Guyeux, Mourad Hakem, David Laiymani, Gilles Perrot, Christian Salim, Bashar Al-Nuaimi, Santiago Costarelli, Carol Habib, Hassan Moustafa Harb, and Ke Du. I would like to express my thanks and my best wishes to Ingrid Couturier for all the received assistance during my study. I would also like to express my thanks to Dr.~Lilia~Ziane Khodja, PostDoc at $LTAS-A\&M$, Liege, Belgium. I would like to thank Béatrice Domenge and Maxim Moureaux from the {\it Reprographie service} for all received assistance during my study. I would also like to thank Patricia Py, Computer Science Department secretary. I dare not risk missing to mention anyone’s name, so I will simply say 'thank you ALL for being there for me'.