Any device that supports data transmission over a serial telecommunications link. Typically, data communications equipment (DCE) refers to modems, Channel Service Unit/Data Service Units (CSU/DSUs), multiplexers, and similar devices. The purpose of a DCE is to provide termination for the telecommunications link and an interface for connecting data terminal equipment (DTE) to the link.
The term «DCE» specifically refers to serial transmission, which generally occurs over links such as a local loop Plain Old Telephone Service (POTS) connection, an Integrated Services Digital Network (ISDN) line, or a T1 line. An example of a DCE is an analog modem, which provides a connection between a computer (the DTE) and the local loop POTS phone line (the serial transmission line). A DCE accepts a stream of serial data from a DTE and converts it to a form that is suitable for the particular transmission line medium being used. The DCE also works in reverse, converting data from the transmission line to a form the DTE can use.