High-Level Data Link Control

This article possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. (March 2019) (Learn how and when to remove this message)

High-Level Data Link Control (HDLC) is a communication protocol used for transmitting data between devices in telecommunication and networking. Developed by the International Organization for Standardization (ISO), it is defined in the standard ISO/IEC 13239:2002.

HDLC ensures reliable data transfer, allowing one device to understand data sent by another. It can operate with or without a continuous connection between devices, making it versatile for various network configurations.

Originally, HDLC was used in multi-device networks, where one device acted as the master and others as slaves, through modes like Normal Response Mode (NRM) and Asynchronous Response Mode (ARM). These modes are now rarely used. Currently, HDLC is primarily employed in point-to-point connections, such as between routers or network interfaces, using a mode called Asynchronous Balanced Mode (ABM).