Buffered or unbuffered: a case study based on log/sub d/(N,e,p) networks

Two implementation styles (buffered and unbuffered) have been used for constructing multistage interconnection networks for ATM switching. Conventional studies have shown that an unbuffered network, while having a simpler design, produces a lower throughput than a buffered network. But most of these studies, based on the assumption that each cell is routed independently (i.e. per-cell routing), ignored the out-of-sequence transmission problem of a buffered network in a virtual-channel environment. One way to keep the packet sequence for a buffered network without adding additional hardware is to fix the path for each virtual channel. We compute the throughput of this approach in designing nonblocking networks and compare it with that of the unbuffered approach. The base of our comparison is log/sub d/(N,e,p) networks. The results show that a fixed-path-routing buffered network will have a throughput even lower than that of an unbuffered network.