Threshold-based Exhaustive Round-Robin for the CICQ Switch with Virtual Crosspoint Queues

A multi-cabinet implementation of a combined input and crosspoint queued (CICQ) switch introduces a large RTT latency between the line cards and switch fabric, requiring a large crosspoint (CP) buffer. A virtual crosspoint queues (VCQs), proposed in literature are shared among a set of virtual output queues (VOQs) and CP buffers for the same input port, reducing minimal memory size required inside the switch fabric. In this paper, a threshold-based exhaustive round-robin (T-ERR) arbitration is employed to improve the throughput of the CICQ switch with VCQs. The T-ERR at VCQ and CP arbiters serves packets residing in a longer queue more frequently than packet residing in a shorter queue. The T-ERR is simple yet drastically increases the throughput of the CICQ switch with small CP buffers. Simulation evaluations with unbalanced traffic show that the throughput of the CICQ switch with VCQs improves from 80% to 94% for CP buffer size of 4 cells and 73% to 83% for CP buffer size of 2 cells for RTT = 64 cell time. Furthermore, its throughput is independent of switch size and RTT. Thus, the proposed scheme makes the scalable implementation of a distributed CICQ switch practical.