In telecommunication, the term data service unit (DSU) has the following meanings:
1. A device used for interfacing data terminal equipment (DTE) to the public telephone network.
2. A type of short-haul, synchronous-data line driver, usually installed at a user location, that connects user synchronous equipment over a 4-wire circuit at a preset transmission rate to a servicing central-office.
Note: This service can be for a point-to-point or multipoint operation in a digital data network.
Source: from Federal Standard 1037C and from MIL-STD-188
