What is the primary function of the Flag in an HDLC header?

The primary function of the Flag in an HDLC header is to list a recognizable bit pattern for new frame detection. The Flag is a unique sequence of bits, specifically the binary sequence 01111110, which serves several critical purposes in HDLC (High-Level Data Link Control) protocol.

Firstly, the Flag indicates the start and end of a frame in the data stream. By using a distinct bit pattern, it allows receiving devices to easily identify where one frame ends and another begins. This is essential for maintaining data integrity and ensuring that frames are processed in the correct sequence.

Secondly, because the Flag must be unique and recognizable, it helps prevent misinterpretation of the data being transmitted. If the same bit pattern were to appear in the data portion of the frame, the receiver would need to manage the potential confusion regarding where the data ends and the frame begins. The unique Flag pattern facilitates accurate alignment and synchronization of the data stream.

Therefore, it’s critical for correctly framing data packets in HDLC, making the Flag an indispensable component for frame detection and delimitation.