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• Bertsimas, D., Gamarnik, D., and Tsitsiklis, J. N., Stability conditions for multiclass fluid queueing networks, IEEE Trans. Automat. Control., 41 (1996), no. 11, 1618-1631.
• Botvich, D. D., and Zamyatin, A. A., Ergodicity of conservative communication networks, Rapport de recherche, 1772, INRIA, (1992).
• Chen, H., Fluid approximations and stability of multiclass queueing networks I: Work- conserving disciplines, Annals of Applied Probability, 5 (1995), 637-665.
• Dai, J. G., On possitive Harris recurrence of multiclass queueing networks: a unified approach via fluid limit models, Mathematics and its applications, 71 (1995), 71-90.
• Dai, J. G., Hasenbein, J. J., and Vande Vate, J., Stability of a three-station fluid network, Queueing Systems, 33 (1999), 293-325.
• Dai, J. G., and Vande Vate, J., Global stability of two-station queueing networks, Lecture Notes in Statistics. Columbia University, New York, Springer-Verlag, 117 (1996), 1-26.
• Dai, J. G., and Vande Vate, J., The stability of two-station fluid networks, Operations Re- search, 48 (2000), 721-744.
• Dai, J. G., and Weiss, G., Stability and instability of fluid models for re-entrant lines, Math- ematics of operations Research, 21 (1996), 115-134.
• Down, D. and Meyn, S.P., Piecewise linear test functions for stability and instability of queueing networks, Queueing Systems, 27 (1997), 205-226.
• Rybko, A. N., and Stolyar, A. L., On the ergodicity of random processes that describe the
• functioning of open queueing networks, Problems on Information Transmission, 28 (1992), no. 3, 3-26.
• Department of Mathematics, Djillali LIABES University of Sidi Bel Abbes, BP. 89,
• Sidi Bel Abbes 22000, Algeria. E-mail address: bouchentouf−amina@yahoo.fr Department of Mathematics, Sciences and Technology University of Oran: Mohamed
• Boudiaf, USTOMB BP. 1505 EL-M’NAOUAR-ORAN, Algeria. E-mail address: sakhi.hanane@yahoo.fr