(HDLC) A general-purpose data link control protocol defined by ISO for use on both point-to-point and multipoint (multidrop) data links. It supports full-duplex, transparent-mode operation. It is used extensively in both multipoint and computer networks. Some manufacturers and other standards bodies still use their own acronyms, e.g. IBM's SDLC (Synchronous Data Link Control), the forerunner of HDLC and ANSI's ADCCP (Advanced Data Communications Control Procedure).