A weighted fair queueing scheduler with decoupled bandwidth and delay guarantees for the support of voice traffic

Abstract

Weighted fair queueing (WFQ) schedulers and shapers have gained wide popularity in current routers and switches because of their advanced quality-of-service features and very low implementation cost. A well-known, intrinsic limitation of WFQ schedulers is the coupling between the bandwidth and delay guarantees that they can provide. Because of this coupling, the support of traffic with low bandwidth and stringent delay requirements, most notably voice, is always problematic with WFQ schedulers. We present the decoupled fair queueing (DFQ) server, which is specifically designed for the support of voice traffic in packet-switched networks. The DFQ server maintains the very low implementation complexity of WFQ schedulers, yet it guarantees low delay to flows requesting relatively low bandwidth. This is achieved by judiciously over-allocating the scheduling rates, and by combining the scheduler with a policer, so as to guarantee that the voice flows only receive the desired bandwidth and do not damage one another, nor the other types of flows that are handled by the server.