Webopedia on Google+Webopedia on TwitterWebopedia on FacebookTech Bytes Blog
Main » TERM » H »

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.

    The Problem with Statistics

    We look at a few of the more troubling aspects of statistics and how these may be used to advance an agenda or skew the facts to someone's... Read More »

    29 Free Android Apps for Cash-Strapped Students

    From wacky alarm clocks to lecture hall tools and after class entertainment, these Android apps are a good fit for a student's life and budget. Read More »

    Sharing Threat Intelligence

    A growing number of startups make the sharing of threat intelligence a key part of their solutions. Read More »

    The 7 Layers of the OSI Model

    The Open System Interconnection (OSI) model defines a networking framework to implement protocols in seven layers. Use this handy guide to compare... Read More »

    Network Fundamentals Study Guide

    Networking fundamentals teaches the building blocks of modern network design. Learn different types of networks, concepts, architecture and... Read More »

    Computer Architecture Study Guide

    This Webopedia  study guide describes the different parts of a computer system and their relations. Read More »