Bandwidth allocation for guaranteed versus best effort service categories

Modern communication networks evolve towards integration of guaranteed-perf ormance and best-effort service types. The coexistence of these two service types offers substantial benefits, such as resource sharing between servic e classes, and the ability of the user to select an appropriate service cla ss according to its individual requirements and preferences. Notwithstandin g, such interaction gives rise to more complicated system behavior and rela ted performance issues, which need to be explored and understood in order t o allow efficient network operation. In this paper we examine potential con gestion phenomena, which arise due to the combined effect of bandwidth shar ing and user migration between service classes. We propose a simplified flu id model for session flow, consisting of two coupled queues with state-depe ndent flows, which captures the essential ingredients of service-class inte raction. Our analysis shows that the system might exhibit bistable behavior , in the sense that transient congestion may stir the system from a stable and efficient operating point to an inefficient and congested one. We ident ify conditions which give rise to bistability, and propose a call admission control scheme which prevents the system from getting trapped in a congest ed-type equilibrium, while not interfering with normal system operation.