HDLC Last modified: Tuesday, April 29, 1997
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.
•E-mail this definition to a colleague• For internet.com pages about HDLC . Also check out the following links! HDLC LAPB Level 2 protocol Describes HDLC Link Access Procedure Balanced (LAPB). HDLC Overview Provides an overall description of the HDLC protocol including details on the basic framing structure. SDLC protocol overview Describes the HDLC implementation of SDLC (HDLC Normal Response Mode).	Networking Standards communications protocol frame OSI Give Us Your Feedback Routers HDLC Products Shop by Top Models: Adtran NetVanta 3120 Router 17 store offers from $368 - $606 Adtran NETVANTA 3120 Router 12 store offers from $373 - $700 ADTRAN 1202890E1 Router 14 store offers from $1742 - $2435 Adtran Netvanta® 3430 Router 11 store offers from $627 - $1079 3Com 5012 Router 9 store offers from $195 - $798