Packet scheduling in a low latency optical packet switch

In this paper, we study packet scheduling in the OpCut switch, a recently proposed optical switching architecture that can be adopted for high-performance parallel computers. The key feature of the OpCut switch is that it allows packets to cut-through the switch whenever possible, such that packets experience minimum delay. Packets that cannot cut-through are received by optical receivers and stored in the electronic buffer, and can be sent to the output ports by the optical transmitters later. Due to its feed-back buffer structure, existing scheduling algorithms cannot be directly applied to the OpCut switch. Keeping packet order also becomes more challenging in the OpCut switch. In this paper, we propose a scheduling algorithm for the OpCut switch that achieves overall low packet latency while maintaining packet order. The scheduling algorithm is very simple and can be implemented in hardware. To relax the time constraint on computing a schedule, we further propose a mechanism to pipeline the packet scheduling in the OpCut switch by distributing the scheduling task to multiple “sub-schedulers.” Our simulation results show that the OpCut switch with the proposed scheduling algorithms achieve chose performance to the ideal output-queued (OQ) switch in terms of packet latency, and that the pipelined mechanism effectively reduces scheduler complexity while maintaining satisfactory system performance.