Enrique Vallejo asked an interesting question a while ago:
When was X.25 official declared dead? Note that the wikipedia claims that it is still in use in parts of the world.
Wikipedia is probably right, and had several encounters with X.25 that would corroborate that claim. If you happen to have more up-to-date information, please leave a comment.
More than two decades ago (IIRC before MPLS/VPN was on the drawing board), I was doing some consulting for a service provider specialized in building global IP-based VPN networks for aviation industry1. They ran a well-designed IP-only network but mentioned that they still support X.25 over TCP (XOT). I thought X.25 was dead by that time, but it turned out a large percentage of check-in terminals still used it.
Aside: X.25 was an ideal connectivity solution for check-in terminals:
- You were billed by the usage and usually didn’t have to pay a fixed recurring fee for expensive circuits going to airfields out in the boondocks.
- Bandwidth requirements were minimal. In those days people didn’t have a problem with memorizing three-letter CLI commands2.
- X.25 was so reliable that you could run it over a barbed wire with severe error rate or packet loss that would make TCP stall in a second.
Fast forward at least 15 years. During an intro chat in one of my Expert Express engagements the networking engineer I was working with mentioned that they still supported X.25 (again, using XOT). My immediate reaction was “do you work for an airline?” to which he replied “no, at an airport, but how did you know?” They were still using check-in terminals with X.25 uplinks, and I’m positive some of those terminals are still in use today.
Finally, a bizarre fact: France Telecom shut down Minitel in 2012, at which time the service still had 800.000 terminals, and some POS credit card terminals used underlying X.25 network which was also discontinued (see comment by Pierre).
Let me just mention that Tim Berners-Lee had a working WWW implementation in late 1990 – it took Minitel service over 20 years to be taken over by The Internet.
Speaking of Barbed Wire
Parts of the X.25 protocol stack are used in environment with error rate resembling what you would expect from a barbed wire connection (VHF/UHF radio links):
- AX25 is used by amateur radio operators to run packet radio networks (HT: ICT4F Marcus).
- X.25 is part of the VHF Data Link (aircraft-to-ground data links) protocol stack (see comment by Bela Varkony).
- Added further X.25 use cases based on readers’ comments