(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)