SRR: An O(1) Time Complexity Packet Scheduler for Flows in Multi-Service Packet Networks

Manuscript received May 25, 2002; revised November 27, 2002. This work was supported by the 863 Program of China under contract number 863-300-02-04-99. This paper was presented in part at the ACM SIGCOMM 2001, San Diego, CA, August 2001. The author was with the Institute of Communications Engineering, Nanjing 210016 China. He is now with the Wireless and Networking Group of Microsoft Research Asia, Beijing 100080 China (email: [email protected]). Abstract In this paper, we present a novel fair queueing scheme, which we call Smoothed Round Robin (SRR). Ordinary round robin schedulers are well known for the burstiness of their scheduling output. In order to overcome this problem, SRR codes the weights of the flows into binary vectors to form a Weight Matrix, and then uses a Weight Spread Sequence (WSS), which is specially designed to distribute the output more evenly, to schedule packets by scanning a Weight Matrix. By using the WSS and the Weight Matrix, SRR emulates the Generalized Processor Sharing (GPS) well. SRR possesses better short-term fairness and scheduling delay properties in comparison with various existing round robin schedulers. At the same time, SRR preserves O(1) time complexity by avoiding the time-stamp maintenance employed in various fair queueing schedulers. Simulation and implementation experiments show that SRR provides good mean end-to-end delay for soft real-time services. SRR can be implemented in high-speed networks to provide quality of service (QoS) due to its simplicity and low time complexity.