Bandwidth allocation for guaranteed versus best effort service categories

Modern communication networks evolve towards integration of guaranteed-performance and best-effort service types. The co-existence of these two service types offers substantial benefits, such as resource sharing between service classes, and the ability of the user to select an appropriate service class according to its individual requirements and preferences. Notwithstanding, such interaction potentially complicates the system behavior, and gives rise to subtle optimization questions, which need to be explored and understood in order to allow efficient network operation. In this paper we address some essential performance and flow control issues associated with such service interactions. We propose a fluid model for session flow, which captures the two interaction mechanisms of resource sharing. In particular, our model incorporates the possibility of session migration, where sessions may shift from best effort to guaranteed performance service due to congestion experienced in the former. Within this model, we analyze the system performance and characterize its steady state behavior. We further show that under certain conditions the system exhibits bistable behavior, where some transient congestion may stir the system from a stable and efficient operating point to an inefficient and congested one, which might persist indefinitely. For the latter case, we propose a call admission control scheme which prevents the system from getting trapped in a congested-type equilibrium, while not interfering with normal system operation.