[ih] X.25

[Barbara Denny]

 Packet radio also used logical addressing (see III.C in the referenced paper mentioned below).  It also had something called generic logical addresses which is sorta like anycast.  I don't recall seeing generic logical addresses in use.  I also think from the pr address you could also tell what the attached device was (for example, a station).

J. Jubin and J. D. Tornow, "The DARPA packet radio network protocols," in Proceedings of the IEEE, vol. 75, no. 1, pp. 21-32, Jan. 1987, doi: 10.1109/PROC.1987.13702.

Google search brings up a copy of this paper at Cornell but I am not sure it is reachable anymore.
barbara

    On Thursday, October 2, 2025 at 01:03:06 PM PDT, Jack Haverty via Internet-history <internet-history at elists.isoc.org> wrote:  
 
 Hi Barbara,

Since computer manufacturers were unlikely to offer 1822 interfaces, 
IIRC the non-ARPANET bulk of DDN used X.25 as the interface to PSNs 
(IMPs).  The "DDN X.25 Host Interface Specification" published in 1983 
was the equivalent to the old 1822 document.  It's available at 
https://apps.dtic.mil/sti/tr/pdf/ADA137427.pdf

There's lots of detail in that spec of how hosts (including gateways) 
could use DDN.  But of course it doesn't contain any information about 
how X.25 was actually used in particular hosts as DDN was built out.

One of the less well-known ARPANET IMP features was "Logical 
Addressing", which enabled host computers to be accessible even if they 
changed their Host/IMP connections.  It was essentially a translation 
from a logical address space to the physical one of the moment.

That feature was also present in DDN, but I don't remember how it was 
used.  Appendix A of ADA137427 has a lot of details, including Logical 
Addressing, which may help you remember how the actual testbed in 
Germany was set up.   Appendix B details how a synchronous link could be 
used, which may have been helpful for connecting routers.

/Jack

On 10/2/25 12:28, Barbara Denny via Internet-history wrote:
>  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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