High-level Data Link Control : bit
based line protocol that run on synchronous serial link.
→ The protocol is independent of
any set of characters
→ Packets can be transmitted
transparently. The “0-bit insert method” for transparent
transmission can be implemented based on hardware.
→ The full-duplex communication can
be implemented. Data can be transmitted continuously without waiting.
The data transmission on the link is highly efficient.
→ All the frames adopt CRC check.
The frames are numbered. Thus no frame is lost or received
repeatedly. The transmission reliability is high.
→ The transmission control is
separated from processing, which makes HDLC flexible and
controllable.
| Flag | Address | Control |
Information | FCS | Flag |
01111110 01111110
Types of HDLC Frame
→ Information frame : transmit the
valid information or data
→ Supervisory frame : control
errors and traffic. First two bit of the control field: “10”. [48
bits]
→ Unnumbered frame : used to
establish, delete, and control the link.
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