The Free On-line Dictionary of Computing (19 January 2023):

High-level Data Link Control
HDLC

    (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).

   [Fred Halsall, "Data Communications, Computer Networks and
   Open Systems" 4th edition, 1996, p.237, Addison-Wesley
   Publishing Co. Reading, Mass., USA].

   (1997-11-09)