[markhahn]

Really? Fully-connected hardware is in buildable (at scale) which we already know from the HPC world. Fat trees and dragonfly networks are pretty scalable, but a 3d torus is a very good tradeofff, and respects the dimensionality of reality.

Bisection bandwidth is a useful metric, but is hop count? Per-hop cost tends to be pretty small.

[zamadatix]

Latency (of different types), jitter, and guaranteed bandwidth are the real underlying metrics. Hop count is just one potential driver of those, but different approaches may or may not tackle each of these parts differently.