Efficient Multicast Support in Buffered Crossbars using Networks on Chip

The Internet growth coupled with the variety of its services is creating an increasing need for multicast traffic support by backbone routers and packet switches. Recently, buffered crossbar (CICQ) switches have shown high potential in efficiently handling multicast traffic. However, they were unable to deliver optimal performance despite their expensive and complex crossbar fabric. This paper proposes an enhanced CICQ switching architecture suitable for multicast traffic. Instead of a dedicated internal crosspoint buffer for every input-output pair of ports, the crossbar is designed as a multi-hop Network on Chip (NoC). Designing the crossbar as a NoC offers several advantages such as low latency, internal fabric load balancing and path diversity. It also obviates the requirement of the virtual output queuing by allowing simple FIFO structure without performance degradation. We designed appropriate routing for the NoC as well as on-chip router scheduling and tested its performance under a wide range of input multicast traffic. Simulations results showed that our proposal outperforms the CICQ architecture and offers a viable architectural alternative. We also studied the effect of various parameters such as the depth of the NoC as well as the speedup requirement for high-bandwidth multicast switching.