[ih] X.25

[Vint Cerf]

in pre-NSFNET days, we ran IP over X.25 (Larry Landweber at University of
Wisconsin, Madison, had a role in that, as I recall).
I don't know whether Larry is on this list.

v


On Thu, Oct 2, 2025 at 5:50 AM Michael Grant via Internet-history <
internet-history at elists.isoc.org> wrote:

>
> From "Jack Haverty via Internet-history"
> <internet-history at elists.isoc.org>
> >When we linked the US and UK gateways over the X.25 public network, cost
> for international X.25 traffic was also a factor.  ARPA paid all the costs
> billed from the US connections, and the UK paid the costs for UK
> connections.   As with the traditional phone calls, the calling party was
> billed for the X.25 calls that they initiated.
> There were 2 ways of using X.25.  One was "pad" which was essentially
> like telnet or a terminal dialup.  Characters you typed on your keyboard
> were sent over and the response displayed on your tty.  And if I recall,
> they were line buffered so it was really line-at-a-time with local line
> editing.  This wasn't what I was referring to.
>
> The other way is using X.25 was as a network layer and that's what I was
> referring to as Jack mentioned above.
>
> What I was curious about was how such a link was treated with respect to
> routing at the X.25 level?  Was it simply a point-to-point link that
> whoever set it up configured the underlying X.25 addresses (the one to
> connect to and the one to expect to see on inbound connections)?  Or was
> it treated as some sort of multi-point-to-multi-point like ethernet but
> without the possibility to broadcast (and hence no arp).  If multipoint,
> how did you know where the other endpoints were?  Was there some "X.25
> routing file" passed around to those who were connected to one-another
> via X.25?
>
> When I was working at COS (The Corporation for Open Systems), everyone
> around me was saying that X.25 was the WAN component of OSI and that
> eventually everyone would be on X.25 and TP (TP0 iirc) would run on top
> of that and the world would be a perfect place.  I never could
> understand how that was supposed to work in the real world.  OSI did not
> exactly have a true equivalent of an IP address.  CLNP had these long
> ass addresses but it was never clear (at least not to me) that (like
> TCP/IP) everything would have a network address that was somehow
> routable.  Oh wait, X.500 directory services would solve that...somehow.
>
> Back to my original question above, back in the day, if you were getting
> on the internet and you had an X.25 line and a bunch of other places did
> too, how did you join that network?  It seems like there had to be some
> file manually passed around that listed all the X.25 addresses were
> associated with which subnet was on the other side.  X.25 was much more
> prevalent in Europe.  I don't recall encountering anyone in the US who
> used it.
>
> To be clear, I'm not referring to an IP routing protocol like RIP, OSPF
> or EGP.
>
> When I worked at COS, I had access to several X.25 lines.  (I also
> happened to be one of the sysadmins and would have loved to get COS on
> the internet via one of those earlier rather than later).  I had several
> Suns that were directly connected to X.25 via synchronous serial lines
> for testing the OSI stack at my disposition. But I don't recall any way
> of using X.25 for IP.  Maybe there was and I just never read those docs.
>   I just don't recall.
>
> We did eventually get COS on the internet via a SIP line to Uunet.
> Prior to that email to COS was via UUCP.  Not X.400.
>
> Michael Grant
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