[ih] X.25

[Barbara Denny]

 Thanks for picking up this thread.  I have been poking around on the net to see if I can find more  things that would jog my memory.  I didn't work on the testbed in Germany, where Cisco routers were connected via x.25, for very long so my memory is not the greatest.  I believe the IP address to X.121 address on the router interface was done by a mapping (I think I just got a piece of paper and I don't remember who produced it).  RFC 1236  seems to have the right info in it even though it is dated much later.  (Reminder: when the testbed was installed the Internet didn't use classless addressing yet.)
https://www.rfc-editor.org/rfc/rfc1236.html
I know around the timeframe of this RFC the military, or at least the army, was more interested in the IETF and trying to find ways to get things into RFCs (including going to least one IETF meeting).

I also found this document on the DDN (Defense Data Network) that some people might find interesting. It mentions in a Note that  PSNs were originally called IMPs.
https://apps.dtic.mil/sti/citations/ADA195849

barbara

    On Thursday, October 2, 2025 at 11:49:25 AM PDT, Carsten Bormann via Internet-history <internet-history at elists.isoc.org> wrote:  
 
 On Oct 2, 2025, at 11:50, Michael Grant via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> But I don't recall any way of using X.25 for IP.

RFC 877 (obsoleted almost a decade later by RFC 1356).

We had X.25 on IBM PCs (connected to Bundespost's Datex-P [1]), connected to our BSD boxes via a serial line with SLIP on it (or just X.28/X.29 on it and UUCP, of course).
(The PCs had a rudimentary speaker, and Datex-P was slow enough that you could usefully hear something from making a click for every packet.
Originally thought as a debugging aid, we left it on as it became operationally useful.
We could hear when Datex-P became degraded as the snow melted and the water crept into the cables…)

Grüße, Carsten

[1]: https://de.wikipedia.org/wiki/Datex-P

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