Bandwidth Allocation for Guaranteed Effort Service Categories versus Best

Modern communication networks evolve to- wards 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 appro- priate service class according to its individual requirements and preferences. Notwithstanding, such interaction poten- tially complicates the stystem behavior, and gives rise to sub- tle 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 mcxhanisms of resource sharing. In par- ticular, our model incorporates the possibility of sessaon ma- gration, where sessions may shift from best effort to guar- anteed 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 ex- hibits bistable behavior, where some transient congestion may stir the system From a stable and efficient operating point to an inefRcient and congested one, which might per- sist indefinitely. For the latter case, we propose a call admis- sion control scheme which prevents the system from getting trapped in a congested-type equilibrium, while not interfer- ing with normal system operation.