[ih] X.25

[Michael Grant]

X.25 has been mentioned a few times on this list in the context some 
IMPs could talk to other IMPs over X.25 and somehow parts of the net 
(arpanet?) were connected over X.25.

X.25 addresses were sort of like phone numbers, they don't map on to IP 
addresses (or IMP/HOST).  And data was charged per packet, per byte, and 
iirc, per connection time.  And it was connection oriented though there 
was a sort of datagram mode called "fast connect".

How was it used in the early Internet?  Was there some static file 
passed around with how to route to something and which X.25 address to 
connect to?  Or was each "link" to other IMPs treated as a point to 
point connection with some configured X.25 address?

When I was working with the OSI protocols, X.25 was somehow supposed to 
be used as a network layer but I never could imagine how that was 
supposed to work in any practical way.  CLNP has a really long address 
that you could embed an X.25 address in but it seemed senseless (if you 
used CLNP). Who would be paying for that if something got routed over 
your link!  It would cost you a fortune!

So I'm curious, how did X.25 fit into things in the early internet?  Was 
it used much?  I just never could understand how X.25 was anything like 
the Internet in the OSI world if you had an X.25 connection.

Michael Grant