Deficit round robin

Deficit Round Robin (DRR), also Deficit Weighted Round Robin (DWRR), is a scheduling algorithm for the network scheduler. DRR is, like weighted fair queuing (WFQ), a packet-based implementation of the ideal Generalized Processor Sharing (GPS) policy. It was proposed by M. Shreedhar and G. Varghese in 1995 as an efficient (with O(1) complexity) and fair algorithm.

In DRR, a scheduler handling N flows is configured with one quantum ${\displaystyle Q_{i}}$ for each flow. This global idea is that, at each round, the flow ${\displaystyle i}$ can send at most ${\displaystyle Q_{i}}$ bytes, and the remaining, if any, is reported to the next round. In this way, the flow of number i will achieve a minimal long term data rate of ${\displaystyle {\frac {Q_{i}}{(Q_{1}+Q_{2}+...+Q_{N})}}R}$, where ${\displaystyle R}$ is the link rate.

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