HDLC-Frame Protocol User's Guide (February 2004)

Using HDLC.FRAME Protocol
Introduction
Chapter 318
Introduction
For a complete description of the communications formats and protocol
disciplines, the reader is referred to the ISO standard mentioned in the
first chapter of this manual.
The HDLC.FRAME protocol is a non-polled, bit oriented protocol. Each
unit transmitted over a Level 1 link is termed a frame. A frame consists
of the following components:
• Opening flag (one byte binary 01111110)
• Data (supplied by higher layer)
• Frame check sequence (2 bytes)
• Closing flag (one byte binary 01111110).
A number of parameters can be configured to control the operation of
ports which make use of the HDLC.FRAME protocol. These parameters
are fully described in Chapter 4, “Protocol Specific Configuration.”
Application Message Headers
The HDLC.FRAME protocol does not use application message headers.
Both transmitted and received messages contain only the data portion of
frames sent across the link. The protocol adds leading and trailing flags
and the checksum to transmitted messages, and removes the same from
received messages.