HDLC High Level Data link Control

High-Level Data Link Control (HDLC) is a bit-oriented data link layer protocol that is widely used in WAN communications. It was developed by the International Organization for Standardization (ISO) and is based on the Synchronous Data Link Control (SDLC) protocol developed by IBM.

HDLC is a full-duplex protocol that operates in either point-to-point or multipoint configurations. It supports error detection and correction, flow control, and synchronization between the sending and receiving devices. HDLC frames consist of a header, a data field, and a trailer.

The header contains the control information for the frame, including the source and destination addresses, frame type, and control information. The data field contains the actual data being transmitted, and the trailer contains the error detection and correction information.

HDLC is a very efficient protocol, with low overhead and a small frame size. It is widely used in point-to-point WAN connections, including leased lines, dial-up connections, and ISDN connections. It is also used as the underlying protocol for other WAN protocols such as Frame Relay and X.25.

One of the advantages of HDLC is that it is a standardized protocol, which means that devices from different vendors can communicate with each other using HDLC frames. It is also a very reliable protocol, with built-in error detection and correction mechanisms that ensure data integrity during transmission.