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Author: Howard C. Berkowitz

Focus: Remote Access & CCIE R&S;

Issue Date: Feb 1, 2023

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X.25: An Oldie but a Goodie

X.25 was introduced as a packet technology in the early 1970s. A class of packet services with far better performance than X.25 was introduced in the 1980s and 1990s. However, it's still worth studying X.25 because it is the direct ancestor of Frame Relay, ISDN, and ATM and a better understanding of X.25 will help you better understand these newer technologies. You will still see X.25 in many international applications and in North American legacy applications. There remain niche applications for parts of X.25, such as sending data over the ISDN D channel. X.25 may also solve the problem of high-error-rate lines, as you might find in high-frequency radio links or terrestrial links in developing countries. LAP-B, the data link, can be quite useful for long-delay paths such as satellites.

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