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_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