Comparing the latency performance of the DTable and DRR schedulers

A key component for networks with quality of service (QoS) support is the egress link scheduling algorithm. An ideal scheduling algorithm implemented in a high performance network with QoS support should satisfy two main properties: good end-to-end delay and implementation simplicity. The deficit round robin (DRR) algorithm is known to have a very little implementation complexity. However, depending on the situation, its latency performance can be very bad. On the other hand, table-based schedulers try to offer a simple implementation and good latency bounds. Some of the latest proposals of network technologies, like advanced switching and infiniband, include in their specifications one of these schedulers. However, these table-based schedulers do not work properly with variable packet sizes and face the problem of bounding the bandwidth and latency assignments. We have proposed a new table-based scheduler, which we have called deficit table (DTable) scheduler, that works properly with variable packet sizes. Moreover, we have proposed a methodology to configure this table-based scheduler to decouple the bounding of bandwidth and latency assignments. In this paper, we review these proposals and present simulation results that show that the DTable scheduler is able to provide a better latency performance than the DRR scheduler, with only a slightly higher implementation and computational complexity.