[ih] X.25

[Brian E Carpenter]

On 14-Oct-25 01:12, John Day wrote:
> Sorry to be so late, just catching up.
> 
> As you know, X.25 only defined the *interface* between a “DCE” (host) and a “DTE” (router). The network could do anything it wanted in between. 

Correct, of course. And further, X.75 defined the interface between two X.25 networks (e.g. at international borders). I don't know what X.75 did about Acks.

    Brian

> Of course, most PTTs didn’t exactly. Although there was some variation in what an Ack meant: was the ack from the remote DTE, the remote DCE, or the local DCE.
> 
> In Datapac’s case, I believe the Ack was from the local DTE.
> 
> Also, one has to be careful about the term “interface”. To the CCITT, it meant between boxes, to the rest of us it meant API, back when API meant API, i.e., the calls at the layer boundary.
> 
> Take care,
> John
> 
>> On Oct 2, 2025, at 16:00, Brian E Carpenter via Internet-history <internet-history at elists.isoc.org> wrote:
>>
>> On 03-Oct-25 06:41, Lyndon Nerenberg (VE7TFX/VE6BBM) via Internet-history wrote:
>>> John Levine via Internet-history writes:
>>>> I was a long time uucp user and I do not ever recall running
>>>> into anyone who used it over X.25.
>>>>
>>>> This web page says that the widely used Taylor uucp
>>>> had an 'x' protocol for X.25 but also says it doesn't work:
>>> Berkeley (I think?) added the 'f' protocol for use over X.25 via
>>> PADs.  It encoded 8-bit traffic into 7-bit values, used xon/xoff
>>> flow control, and probably had a few other quirks I forget.  And
>>> it was certainly used, at least in Canada.  Before CA*net was formed,
>>> the U of Alberta, UBC, U of Waterloo, and probably U of Toronto,
>>> all swapped mail and Usenet over Datapac via UUCP running 'f'.  When
>>> I set up APSS (Alberta Disaster Services), I set up a UUCP link
>>> over Datapac with the UofA running 'f' protocol to relay news amd
>>> mail.  It was a real thing.
>>
>> The irony being that Datapac was merely an X.25 wrapper on an underlying
>> connectionless packet-switched network [1] [2].
>>
>> As others have said, IP over X.25 was fairly common in Europe, for financial
>> or political reasons. In fact several European efforts at everything-over-X.25
>> can be found in the two relevant history books [3] [4].
>>
>>    Brian
>>
>> [1] https://www.cs.auckland.ac.nz/research/groups/CDMTCS/researchreports/download.php?selected-id=884
>> [2] https://ieeexplore.ieee.org/document/6592834
>> [3] http://ictconsulting.ch/reports/european-research-internet-history.pdf
>> [4] https://doi.org/10.1002/9783527629336
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