Scheduling latency-critical traffic: a measurement study of DRR+ and DRR++

Efficient fair queuing using deficit round-robin, DRR, proposed by Shreedhar and Varghese (1996) is a low-complexity packet scheduler that has several commercial implementations. DRR has also been extended as DRR+ to accommodate latency-critical flows. DRR+, however, assumes that a latency-critical flow exhibits very smooth arrivals whereas most network flows are very bursty in nature, either as the result of source bursts, or as a result of the dynamics of multihop network paths. When DRR+ encounters a burst, it reverts back to the behavior of DRR, providing no preference or latency bound for latency critical traffic. This is a fatal flaw that prevents DRR+ from being useful in scheduling bursty latency-critical flows. We present a different extension to DRR that has much lower delay and delay jitter than DRR+ and is capable of handling bursty latency-critical flows.