[ih] X.25

[Michael Grant]

>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