if you colocate in their data center, ask them for "ethernet" connectivity. In fact, that's the norm in the hosting world that i'm dealing with.

as far as OCx, that's telco grade transport (connectivity to a data center). if you're looking for serious colocation, try to find a data center that is located in a "carrier neutral" facility. that means they will give you access to multiple IP uplinks (to the internet). hope this helps somewhat.