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HDLC (High-level Data Link Control)

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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

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.

This topic continues in "The Encyclopedia of Networking and Telecommunications" with a discussion of the following:

  • HDLC point-to- point and multipoint (multidrop or one-to-many) connections.
  • HDLC connection methods
  • HDLC framing
  • HDLC sessions
  • HDLC (or its variations) as a data link layer control in various networks
  • LAP-B (Link Access Procedure-Balanced) and LAP-D (Link Access Procedure-D-channel)

Two Internet RFCs are related to HDLC. These are RFC 2687 (PPP in a Real-Time Oriented HDLC-like Framing, September 1999) and RFC 1662 (PPP in HDLC-like Framing, July 1994).

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