A bandwidth-efficient scheduler for MPLS DiffServ networks

DiffServ networks support three forwarding classes: EF (expedited forwarding); AF (assured forwarding); BE (best effort). Scheduling algorithms based on priority queueing, such as Cisco LLQ (low latency queueing) and MDRR (modified deficit round robin), seem to be a natural choice to provide an EF service. The main problem with priority queueing is that, due to lack of service isolation, QoS to AF classes may not be guaranteed if EF traffic is bursty. As an alternative, fair queueing schedulers can provide service isolation and guarantee QoS to all classes by reserving certain bandwidth. However, over-provisioning required by the EF service leads to low bandwidth utilization. We propose a bandwidth-efficient scheduler to provide QoS guarantees to both EF and AF classes. Simulation results show that the proposed scheduler outperforms Cisco MDRR in guaranteeing QoS to AF classes and excels fair queueing schedulers in bandwidth utilization.