You will also run across RBS for Robbed Bit Signalling. It's synonymous with CAS as mike explained. Although I think RBS is a more specific term used for FXO/FXS channels and CAS is a more general/global term. I don't ever recall E&M/Wink-Start circuits being referred to as RBS.
And on a side-note, D4/AMI has 56K per channel, with the 8K being stolen for framing (7-bits per frame with 1-bit reserved for signalling). This is why you don't have PRI on a D4/AMI T1 as computers are based on 8-bits to a byte. D4/AMI audio is transmitted as A-Law as a result.
One day when you are really bored you can read up on PRI, NFAS, SS7, and all the lovely mess that they inspire.
SS7 is the really interesting one. All kinds of madness that goes on in that protocol. I prefer to think of it as carrier-grade VoIP.
