International X.25 (was: UUCP over X25 on Sun 3)

[Carl S. Gutekunst]

[Followups redirected to comp.protocols.iso]

>> The 7-bit-printable-ASCII restriction comes from international X.25 gateways,
>> many of which insist on swiping the eigth bit for parity or somesuch.
>
>It's difficult to believe CCITT is so stupid to allow this in X.25 VCs.

Ah, but this has nothing to do with X.25, and is completely outside the realm
of CCITT. X.25 only describes the connection between a DTE (that is, a host)
and a DCE (a network), and *some* of the behavior between two DTEs (two hosts,
with a network inbetween). The standards deliberately say nothing about what
protocols are used internally in the network, and here is where you get into
trouble. Not only do you have gateways, but you also have network proprietary
protocols. This is very different from ARPANet, where you have TCP/IP riding
on top of an IMP-to-IMP protocol. The DCEs on many public data networks do a
protocol conversion, from X.25 to something deemed more suitable for long-haul
packet switching, or -- more likely -- whatever protocol the network was using
before they started using X.25 to talk to DTEs.

>What happens if one wants to run IP, DECNET, or OSI across such a gateway?
>I guess you don't.

That's right. Note that this *is* changing; I believe we can now run 8 bits
among the U.S. (Tymnet and Telenet) the U.K. (PSS) and Canada (Datapac). But
for amusement I tried Germany again yesterday. All my 8th-bit-on words were
stripped. Curious thing, too -- you *need* all eight bits to get X.25 packet
header through, to say nothing of the 16-bit FCS. But if the network has done
a protocol conversion, almost anything can happen....

<csg>