HDLC Flags

HDLC is a data link protocol which uses a unique bit sequence to delimit the start and end of each PDU transported by the data link layer service. In HDLC, frames are delimited by a sequence of bits known as a "flag". The flag sequence is a unique 8-bit sequence of the form 0111 1110. The way in which this is performed is described in the diagram

(fig)The flags before and after an HDLC frame indicate the start and end of the frame