Legacy Data System Reference - Comtech EF Data
Legacy Data System Reference - Comtech EF Data
Legacy Data System Reference - Comtech EF Data
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<strong>Legacy</strong> <strong>Data</strong><br />
1.1 HDLC Features<br />
HDLC (High-level <strong>Data</strong> Link Control) is a protocol defined by the International Standards<br />
Organization. This protocol is a link-layer protocol having the following features:<br />
• Error detection using a 16-bit, CRC-CCITT, cyclic redundancy check error<br />
detection polynomial.<br />
• Single frame format containing an arbitrary number of bits.<br />
• Frame boundaries defined by a special bit pattern named FLAG (01111110).<br />
• <strong>Data</strong> transparency by means of bit stuffing.<br />
• Address field used to identify the station.<br />
• Control field used for error correction and line establishment.<br />
The HDLC message format is:<br />
01111110 ADDR CTRL DATA CRC 01111110<br />
The HDLC protocol is widely used, and many variations exist (ADCCP, transparent<br />
SDLC, X.25 level II, etc.). The variations differ only in their address and control field<br />
formats.<br />
1-2 Memotec Inc.
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