Leap Forward Virtual Clock : A New Fair Queuing Scheme withGuaranteed Delays and Throughput

Fair queuing is the mechanism by which routers schedule packets on output links in order to guarantee fairness and latency bounds. Fair queuing, along with with address lookup and switching, is one of the major bottlenecks for routers today. We describe an eecient fair queuing scheme, Leap Forward Virtual Clock , that provides end-to-end delay bounds and throughput fairness comparable to the best schedulers described earlier in the literature. More importantly, our scheme can be implemented with a worst-case time O(loglog N) per packet (inclusive of sorting costs), which improves upon all previously known schemes that guarantee delay and throughput fairness. We rst describe how to modify Zhang's seminal virtual clock scheme to provide throughput fairness using using two simple ideas: a quarantine mechanism and a a leap forward mechanism. Then we describe how to improve computational eeciency (with only a small cost in the delay bound) by using coarsened or approximate tags. We describe simulations and implementation measurements that connrm the beneets of our scheme.