Two-by-two switch element connects eight devices in three stages.
Can use a larger radix: benes, clos, shuffle, delta, (even batcher-banyan).
Problem: typically we will not need quite as many initiators as targets. Throughput=no of ports, but fabric may block and there may be receiver contention.
Can be overly complex on the small scale, but scale up well.
Network On Chip Synthesis Tool: Mullins et al.\ NetGen Network Generator.