How smooth is smoothed round robin?

A simulation result in the original paper about SRR indicates that SRR, an O(1) time complexity round robin scheme, is almost as good as the time stamp based WFQ in delay properties. This poses an interesting question of whether the simple SRR-like schemes are able to replace the more complex WFQ-like schemes to provide QoS guarantees in high-speed networks. This is not a straightforward question, however, because the performance of round robin schemes (including SRR) are heavily dependent on network conditions. To obtain meaningful results, one has to explore the whole parameter space. We describe network conditions in two dimensions: traffic patterns and weight distributions. We conduct extensive simulations systematically in a variety of scenarios in terms of traffic patterns and weight distributions, to investigate the performance of SRR as compared with deficit round robin and WF²Q+. It is shown that under most cases SRR has delay performance approximating WF²Q+ and better than DRR.