Performance evaluation of crossbar switch fabrics in core routers

Many researchers have pointed out that using complex scheduling algorithms in input queuing switches with VOQ (Virtual Output Queuing) can achieve 100% throughput. But these algorithms are too complex to be implemented in hardware. In this paper, based on combined input/output queuing (CIOQ) switch fabrics, we propose a simple scheduling algorithm named OPRR (Outlet Priority Round Robin). For the synthetic workloads we consider, including uniform and bursty traffic models, the performance of OPRR in VOQ and single queue mode is evaluated respectively. Through the simulation results we show that 1) OPRR algorithm, coupled with a speedup of 2, can lead to performance very close to output queuing switches, and 2) under the same condition the single queue mode behaves almost identically to VOQ mode. These results are very useful to direct the design and implementation of switch fabrics in core routers.