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HDLC is a bit-oriented, link layer protocol for the transmission of data over synchronous networks. It is an ISO standard, but is a superset of IBM's SDLC (Synchronous Data Link Control) protocol. SDLC was the successful follow-up to the BISYNC communication protocol and was originally introduced with IBM SNA (Systems Network Architecture) products. Another name for HDLC is ADCCP (Advanced Data Communications Control Procedure), an ANSI standard, but HDLC is the widely accepted name for the protocol. There are some incompatibilities between SDLC and HDLC, depending on the vendor.