A data service unit, sometimes called a digital service unit, is a piece of telecommunications circuit terminating equipment that transforms digital data between telephone company lines and local equipment.
The device converts bipolar digital signals coming ultimately from a digital circuit and directly from a Channel service unit (CSU), into a format (e.g. RS- 530) compatible with the piece of data terminal equipment (DTE) (e.g. a router) to which the data is sent.
The DSU also performs a similar process in reverse for data heading from the DTE toward the circuit.
The telecommunications service a DSU supports can be a point-to-point or multipoint operation in a digital data network.
Most DSUs also allow various data patterns to be generated and monitored to measure error rate of the communication link.