When receiving DID service from the CO on other than analogue trunks, this is how it is done. Using a conventional DS1, each channel is configured as a 4wire E/M path. Each channel has its own signalling and network addressing. This comes from the TRUNK side of the CO switch (all trunking does). It is how it is configured that determines its use. This is how "Supertrunk" is provisioned.
The term CAS is a "Ciscoism" that means Channel Associated Signalling. Cbeyond uses Cisco 2800 series access routers and adopted their jargon.
Now, an other point of information, all trunking on all digital CO switches (4ESS, 5ESS, DMS10, DMS100, DMS200, DMS250, DEX600, etc.) comes out as DS1 at that level. So when you order "analogue" DID trunks, they come from a Channel Bank and the Channel Unit, a DPT (Dial Pulse Terminate) connects to the local loop pair to the premise.
....JIM....