Is X.25 Still Alive?
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
A similar design is described in the Dedicated-Router Approach to Peer-to-Peer Model in Chapter 7 of the original MPLS and VPN Architectures book. ↩︎
Looking for some fun reading full of cryptic 3-7 letter commands? Check out The Complete Amadeus Manual. ↩︎
i actually worked there as a designer/implementer.. it was the predecessor of MPLS VPNs.. L2 VPNs using X25 and FR including the precursors to VoiP which was VoFR... We also built L3 IP VPNs for larger networks using BGP but with standard communities. At the time iirc we were coming towards scaling limit's and that may have been one of the driving reasons the MPLS/VPNs and RTs.?
The network was known as the biggest Cisco network in the world and also used something called the ALPS protocol suite in the airline VPNs.
The technology over these FR/ATM networks were such things as DLSW, DECNET et al and when IP we used EIGRP vs OSPF as the routing protocol.
One thing sorely lacking there which i discovered in my next engagement was no interaction with he physical layer. It was pure logical design and config. And also a very good place to learn to become a CCIE at the time.
we also ran debug all to learn what we were doing due to lack of decent docs.
X.25 has just been introduced recently in air traffic management for air-ground data links as part of the VDLm2 protocol stack. It uses a special profile of X.25 and OSI on top of it.
It will stay with us up to 2030 as a minimum. It might be upgraded to IPv6 in the network layer, a new standard is under discussion. Or it might be replaced by LDACS.
See also https://www.datalinkservices.eu/
The world of aircraft can be strange. There is also AFDX - Ethernet made deterministic using ideas from ATM, with a multicast overlay virtualisation which is used as forwarding destinations instead of MAC addresses.
I remember it was used for POS/payment terminals back in the time. A retail customer I was dealing with had an outage in 2012 when they stopped Transpac (the french X25 network that powered the Minitel), because its terminals were using it. We had to think about XOT and find a third party provider... :-)
Not sure what this means, but it would appear that support for X.25 and XOT was added by Cisco for ISR 4000 in IOS XE 16.10.1a at the end of 2018 ?!
https://www.cisco.com/c/en/us/td/docs/routers/access/4400/release/xe-16-10/isr4k-rel-notes-xe-16-10.html <snip> New Software Features in Cisco 4000 Series ISRs Release Cisco IOS XE Gibraltar 16.10.1a The following features are supported by the Cisco 4000 Series Integrated Services Routers for Cisco IOS XE Gibraltar 16.10.1a: Cisco X.25 & XOT Support on Cisco 4000 Series ISRs—For detailed information, see the following Cisco document: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/wan_smxl/configuration/xe-16-10/wan_smxl_xe16_10_book/wan-smxl-overview.html. </snip>
It means that a large-enough customer probably focused on aviation industry wanted to replace 3600s with ISRs and told Cisco "there's no PO without XOT support"