Deficits for bursty latency-critical flows: DRR++

Fair queuing was invented to ensure that every flow gets its fair share of the total bandwidth. Efficient fair queuing using deficit round-robin, DRR, proposed by Shreedhar and Varghese (see IEEE/ACM Trans. Net., vol.4, no.4, p.386-97, 1996), reduces the work to process each packet from O(log(n)) to O(1). DRR+ was also extended to accommodate latency-critical flows. DRR+ uses a timer to police each latency-critical flow and was shown to have a latency bound of (n/sub c/s)+(M/B) for these flows. The definition of the contract of Shreedhar and Varghese, however, constrains a latency-critical flow to generate very smooth arrivals. By giving another definition of contract, we return to using the original concept of deficit to enforce each flow's commitment to its contract. This allows for bursty arrivals which may occur either as the result of source bursts, or as a result of the dynamics of multihop network paths.