PCRRD: a pipeline-based concurrent round-robin dispatching scheme for Clos-network switches

This paper proposes a pipeline-based concurrent round-robin dispatching scheme, called PCRRD, for Clos-network switches. Our previously proposed concurrent round-robin dispatching (CRRD) scheme provides 100% throughput under uniform traffic by using simple round-robin arbiters, but it has the strict timing constraint that the dispatching scheduling has to be completed within one cell time slot. This is a bottleneck in building high-performance switching systems. To relax the strict timing constraint of CRRD, we propose to use more than one scheduler engine, up to P , so called subschedulers. Each subscheduler is allowed to take more than one time slot for dispatching. Every time slot, one out of P subschedulers provides the dispatching result. The subschedulers adopt our original CRRD algorithm. We show that PCRRD preserves 100% throughput under uniform traffic of our original CRRD algorithm, while ensuring the cell-sequence order. Since the constraint of the scheduling timing is dramatically relaxed, it is suitable for high-performance switching systems even when the switch size increases and a port speed is high (e.g., 40 Gbit/s). Keywords— Packet switch, Clos-network switch, dispatching, arbitration, pipeline, throughput