A non-uniform traffic oriented scheduling algorithm in combined input-crosspoint-queued (CICQ) switches

Abstract

Combined input-crosspoint-queued (CICQ) switch structure decouples the inputs and outputs matching and enables totally distributed arbitration. CICQ switch cannot achieve 100% throughput under non-uniform traffic if Round-Robin (RR-RR) algorithm is used. The other existing schemes require quite a bit of hardware and time complexity. In this paper, we theoretically prove that the RR-RR can achieve 100% throughput under uniform traffic, but it would be instable under non-uniform traffic. Our quantitative analysis also points out that the throughput will be < 91.7% under the weak diagonal traffic model with f = 0.5 and k = 2, where f is the packet arrival rate along the main diagonal of the traffic matrix and k is the number of buffers used in each crosspoint. Moreover, our formula shows that the k must be at least 4 and 24, respectively, if we wish to improve the throughput to 95 and 99%. Based on our theoretical study, we propose the Differential Round-Robin (DRR) algorithm. Simulations have demonstrated that DRR can achieve 100% throughput under arbitrary traffic using only one buffer cell in each crosspoint. DRR algorithm keeps the high simplicity and efficiency of RR-RR with O(1) complexity while overcoming the instability problem of RR-RR.