HDLC – High-level Data Link Control

Short for High-level Data Link Control, a transmission protocol used at the data link layer (layer 2) of the OSI seven layer model for data communications. The HDLC protocol embeds information in a data frame that allows devices to control data flow and correct errors. HDLC is an ISO standard developed from the Synchronous Data Link Control (SDLC)standard proposed by IBM in the 1970’s.

For any HDLC communications session, one station is designated primary and the other secondary. A session can use one of the following connection modes, which determine how the primary and secondary stations interact.

  • Normal unbalanced: The secondary station responds only to the primary station.
  • Asynchronous: The secondary station can initiate a message.
  • Asynchronous balanced: Both stations send and receive over its part of a duplex line. This mode is used for X.25 packet-switching networks.
  • The Link Access Procedure-Balanced (LAP-B) and Link Access Procedure D-channel (LAP-D)protocols are subsets of HDLC.

    Top Articles

    Huge List Of Texting and Online Chat Abbreviations

    From A3 to ZZZ we list 1,559 text message and online chat abbreviations to help you translate and understand today's texting lingo. Includes Top...

    How To Create A Desktop Shortcut To A Website

    This Webopedia guide will show you how to create a desktop shortcut to a website using Firefox, Chrome or Internet Explorer (IE). Creating a desktop...

    The History Of Windows Operating Systems

    Microsoft Windows is a family of operating systems. We look at the history of Microsoft's Windows operating systems (Windows OS) from 1985 to present...

    Hotmail [Outlook] Email Accounts

      By Vangie Beal Hotmail is one of the first public webmail services that can be accessed from any web browser. Prior to Hotmail and its...

    Legacy Code Definition &...

    Legacy code refers to source code that has been inherited from a previous...

    Unregulated Power Supply Definition...

    An unregulated power supply is a system that transforms input voltage into direct...

    Cybersecurity Awareness Training Definition...

    Cybersecurity awareness training informs employees of the attack surfaces and vectors in their...