Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!pacbell!att-ih!ihnp4!ihlpl!jhh
From: jhh@ihlpl.ATT.COM (Haller)
Newsgroups: comp.protocols.iso
Subject: Re: International X.25 (was: UUCP over X25 on Sun 3)
Message-ID: <4680@ihlpl.ATT.COM>
Date: 25 Apr 88 15:40:47 GMT
References: <20060@pyramid.pyramid.com> <18471@watmath.waterloo.edu> <20532@pyramid.pyramid.com>
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 30
Summary: X.25 states rather explicitly that networks cannot muck with your data

In article <20532@pyramid.pyramid.com>, csg@pyramid.pyramid.com (Carl S. Gutekunst) writes:
> [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).

If the network is not passing the eighth bit transparently, it's not X.25.

From the 1980 yellow book and the 1984 red book, X.25 section 4.3:

	Normal network operation dictates that user data in data and
	interrupt packets are all passed transparently, unaltered through
	the network in the case of packet DTE to packet DTE communications.

There is a similar statement in section 3.3 of X.75 in the red book,
so there is no excuse for a network not to pass all bits transparently.
Of course, all bets are off if any data passes through a PAD at either
end of a connection.  Given the intransigence of the German PTT, and
the difficulty of certifying a computer's X.25 to their satisfaction,
I would not be suprised if there was a PAD at the other end.

John Haller
Accunet(r) Packet Service Development
att!ihlpl!jhh