Few days back I made a trip to a very large data center and was somewhat overwhelmed by the complexity of routers, switches, DSUs, modems, mainframe and some devices that I even couldn't recognize

The one thing that scared me was the cabling to interconnect many devices. As the guy explained the sequence of connections, I looked like a deer in the headlight

When it comes to cabling routers, switches, telco and modems interconnections, what should I know as a MUST. I admit I don't know a lot about cabling, but at least I'm willing to learn.