Questions about the US university computer network

[Majestic XII]

I've been trying to find (okay, 5mins on google) a site about the university computer network in the US. Figures like speed, traffic and how its built would be great. I suppose its up to each state to build their own network, but how do they connect each state? Through commercial fiber or dedicated fiber?

They are upgrading the computer network connecting all the Unis here, so it would be interesting to see how they do it in other countries.