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1-4-3 HDLC (High-Level Data Link Control)

HDLC (High-level Data Link Control) is a transmission control procedure that is used when high-speed transmission of data is performed by transmitting data in units of frames.

(1) Format of frames

According to HDLC, the frames having the following format become the unit of transmission.

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F : Flag sequence (8 bits) It is the start/end flag (01111110) that is added at the beginning and end of the frame. A : Address field (8 bits) The address of the transmitting station or receiving station of the frame is recorded. C : Control field (8 bits) The type and transmission sequence of the frame is recorded. I : Information field (any arbitrary n bits) The transmission data is recorded. FCS: Frame Check Sequence (16 bits) The CRC code for error control of the A, C, and I fields is recorded. · 1 question

(2) Types of frames

Depending on the purpose, the frames that are used in HDLC can be classified into the following three types.

(3) Establishing a data link

According to HDLC, the computer (or terminal) to be connected is called a station. The method of establishing a data link differs according to the type of the station.

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According to HDLC, continuous transmission of information (i.e., frames) is possible by using the information (transmission sequence number/reception sequence number) of the control field after a data link is established.