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 perfor-mance network with QoS support should satisfy two main properties: good end-to-end delay and implementation sim-plicity. 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 sched-ulers do not work properly with variable packet sizes and face the problem of bounding the bandwidth and latency as-signments. 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 la-tency assignments. In this paper, we review these proposals and present sim-ulation results that show that the DTable scheduler is able to provide a better latency performance than the DRR sched-uler, with only a slightly higher implementaion and compu-tational complexity. This work was partly supported by the Spanish CICYT under CSD2006-46 and TIN2006-15516-C04-02 grants, by Junta de Comunidades de Castilla