C
CAS Channel Associated Signalling
CAPS Call Attempts Per Second
CCF Charging Control Function (IMS)
CEGW Capability Exposure Gateway (IMS)
CES Circuit Emulation Service
CDR Call Detail Record
Centrex Central Exchange. A method of operating a virtual PBX so the customer doesn't have to maintain their own PBX.
CLD Calling Line Display
CLI Calling Line Identify
CMS Content Management System
CMTS Cable Modem Termination System
COPS Common Open Policy Service
CP Communication Provider
CPE Customer Premise Equipment
CPU Central Processing Unit
CRDB Central Routing Database (also see ENUM)
CUPID Communication Provider ID