UNIcations, hardware> (CSU/DSU, or "..digital..") A device that performs both the channel service UNIt (CSU) and data service UNIt (DSU) functions. The Channel Service UNIt (CSU) is used to terminate a DS1 or DS0 (56/64 kb/s) digital circuit. It peforms line conditioning, protection, loop-back and timing functions. The Data Service UNIt (DSU) terminates the data circuit to the Data Terminal Equipment (DTE) and converts the customer' s data stream into a bi-polar format for transmission. (2001-10-19)