[ih] How long did it take?

[Brian E Carpenter]

Yes, IP over X.25/X.75 was a thing for a while in Europe, for example when you couldn't get an international leased line because of PTT or funding agency politics.

But Olivier is correct, JANET Coloured Book protocols were a better way to use X.25, which was a good reason why the UK transition to TCP/IP was a little delayed (and partly why we had to run application layer gateways for email and file transfer at CERN).

Regards/Ngā mihi
    Brian
On 18-Sep-26 06:05, Craig Partridge via Internet-history wrote:
> On Thu, Sep 17, 2026 at 11:28 AM Dave Crocker via Internet-history <
> internet-history at elists.isoc.org> wrote:
> 
>>
>>> I failed to see how X.25 could be used as an internet.
>>
>> IP/X.25, using X.25 as a link layer.  For CSNet, Purdue wrote a Unix
>> driver to do that.
>>
>> For the original CSNet email service, everything was dial-up, but that
>> quickly included dial-up to a commercial x.28/x.29 commercial service.
>> This meant that MMDF's packetized phonenet link layer ran on top of the
>> commercial X.25 packet service.
>>
>> That is, one packet layer over another.  Purdue's driver similarly was
>> packet over packet.  We each, separately discovered how important it was
>> to make sure the top layer packet was no larger than the bottom layer
>> one, if possible.  Otherwise, it doubled the commercial service's packet
>> count, and charging was by the packet...
>>
>> d/
>>
> 
> CSNET used that Purdue code to connect a handful of CSNET sites to the
> Internet.
> 
> As I recall, and my memory on this is rather hazy, some of those sites were
> in Europe so we went from an X.25 provider (AT&T) in the US to an X.25
> provider in Europe.  This meant we went through an X.75 gateway that only
> allowed, as I recall, *two* X.25 packets in flight in each direction (and
> the pages were small - 128 or 256 bytes).  (It is useful to recall that
> X.75 terminated the X.25 connections, so it keeping the window small was
> important to limit buffering).  So fragmented IP datagrams over X.25 with a
> serious delay-bandwidth constraint.  Again, if memory serves, delays were
> long (200ms or so).  It worked out to about 8Kbps.
> 
> Over time, the reaction was what you'd expect: (a) customers pushed to use
> premium dialup modems (the Trailblazer in the late 1980s could hit
> 19.2Kbps); (b) dialup SLIP; and (c) leased lines.
> 
> Craig
> 
>