Fast and noniterative scheduling in input-queued switches: Supporting QoS

Abstract

We report three fast and scalable scheduling algorithms that provide exact bandwidth guarantee, low delay bound, and reasonable jitter in input-queued switches. The three schedulers find a maximum input/output matching in a single iteration. They sustain 100% throughput under both uniform and bursty traffic. They work many times faster than existing scheduling schemes and their speed does not degrade with increased switch size. SRA and SRA+ algorithms are of O(1) time complexity and can be implemented in simple hardware. SRA tends to incur different delays to flows of different classes of service due to their different subscribed portions of the total bandwidth. SRA+, a weighted version of SRA, operates on cells that arrive uniformly and on cells of packets such that the cells of whole packets are switched contiguously. SRA+ improves over SRA in that all flows undergo the same delays regardless of their bandwidth shares. The schedulers operate on queue groups at the crossbar arbiters in a distributed manner.