Proportional Nested Deficit Round Robin: Improving the Latency of Packet Scheduler with an O(1) Complexity

In recent years, many fair packet scheduling algorithms have been proposed for switches and routers to provide the quality of service (QoS) guarantees required by many applications. In addition to the fairness and low end-to-end delay that these algorithms have to have, simplicity and scalability are two significant factors that play an important role. In this paper, we present a new scheduling discipline called proportional nested deficit round robin (PNDRR), which has a low latency and reduces burstiness. PNDRR is a class of nested-DRR in which each DRR round is split into some smaller inner rounds. However, unlike nested-DRR, flows receive credits proportional to their deficit counters in each inner round. PNDRR takes advantage of the input traffic pattern and decreases the serving size of flows when the input traffic contains many small packets. This helps to interleave packets in many practical scenarios, such as the Internet, where the majority of packets are relatively small. The latency and fairness of PNDRR are studied and compared to other algorithms using simulation. PNDRR has a per-packet computational complexity of O(1)