I didn't build it, but if I ever have to build one, I know how it's going to be done. Our core is so meshed that it looks like a spider web when it's put into Visio. It's crazy really, overkill to the extreme. We're working on VLANing everything now, so we have a big task ahead of us.
BTW, we've got more dark fiber than we know what to do with. Every single site (400+) has at least 12 pair of fiber run to it.
You may bust my chops on total carrier circuits, but I have one hell of a MAN going on. 😉😀