Abbrev. for digital data communication message protocol. A data link control protocol developed by Digital Equipment Corporation. It is similar to SDLC and HDLC but is character-oriented rather than bit-oriented. It allows a variety of data link characteristics: full duplex or half duplex, asynchronous or synchronous, switched or dedicated, point-to-point or multipoint, and serial or parallel. Data transparency is achieved using a data-length field rather than bit or byte stuffing techniques. Active NAKs are used for error control, in addition to timeouts.