Enhanced Weighted Round Robin schedulers for bandwidth guarantees in packet networks

Abstract

Because of their minimal complexity, Weighted Round Robin (WRR) schedulers have become a popular solution for providing bandwidth guarantees to IP flows in emerging networks that support differentiated services. The introduction of applications that require flexible bandwidth management puts emphasis on hierarchical scheduling structures, where bandwidth can be allocated not onlyto individual flows, but also to aggregations of those flows. With existing WRR schedulers, the superimposition of a hierarchical structure compromises the simplicity of the basic scheduler. Another undesirable characteristic of existing WRR schedulers is their burstiness in distributing service to the flows. In this paper, we present two enhancements for WRR schedulers which solve these problems. In the first enhancement, we superimpose a hierarchical structure by simply redefining the way the WRR scheduler computes the timestamps of the flows. This "soft" hierarchy has negligible complexity, since it does not require any additional scheduling layer, yet is highly effective. The second enhancement defines an implementation of a WRR scheduler that substantially reduces the service burstiness with marginal additional complexity. © Springer-Verlag Berlin Heidelberg 2001.