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From: barns@GATEWAY.MITRE.ORG (Bill Barns)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  DDN X.25 question.
Message-ID: <8904181532.AA01400@gateway.mitre.org>
Date: 18 Apr 89 15:32:14 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 58

I think you have become lost in CCITT/ISOspeak.  This is no reflection
on your intelligence or diligence; their nomenclature is considerably
less than lucid.

I'm not sure where you got your #1 from in 8208, but I'm speculating
that you are looking near the end of clause 15.1.  The statement
actually made there is that "requests for X.25 facilities must precede
the other requests and requests for CCITT-Specified DTE facilities must
follow the other requests."  In both 8208 and 1984 X.25, X.25
facilities and CCITT-Specified DTE facilities are two disjoint subsets
of the facilities discussed in the documents.

By X.25 facilities, they mean those discussed in clauses 6 and 7 of
X.25(1984), which correspond to clause 13 of 8208.  By CCITT-Specified
DTE facilities, they mean those discussed in Annex G of X.25(1984),
which corresponds to clause 14 of 8208.  So the "non-X.25 facilities"
(which as you correctly deduced, is what the DDN Type of Service and
Precedence facilities are) are requested with "other requests".

Translation: The X.25 facilities come first, the non-X.25 facilities
(such as DDN's) come second, and the CCITT-Specified DTE facilities
come third.

Bear in mind that when the DDN X.25 spec in the Handbook was written,
X.25(1984) wasn't out yet.  Before X.25(1984), there was no such thing
as a "CCITT-Specified DTE facility" and thus no reason to clarify where
the DDN non-X.25 facilities belong in relation to them.  So, when the
DDN spec refers to "all CCITT X.25 facilities", it's unambiguous in
the author's frame of reference.  And strictly speaking, it isn't wrong
now, if you parse it as  (all (CCITT (X.25 facilities)))  rather than as
(all ((CCITT X.25) facilities))  since the CCITT-Specified DTE facilities
are not X.25 facilities even though CCITT specifies them in Annex G of
Rec X.25 and Annexes are considered an integral part of Recommendations.

Sigh.

(Fine print:  CCITT specifies the coding of the CCITT-Specified DTE
Facilities, but does not specify the procedures for using them, in the
CCITT sense of the word "procedures".  That issue is considered to be
in the realm of "international user organizations" by which they mean
ISO.  Likewise, they don't tell you how the two types of "other
requests" are positioned in relation to each other, only where they all
are in relation to the facilities which are in their domain to specify.
So the relative position of calling-DTE-specific-non-X.25-facility-requests
and called-<what I just said> is a local network matter.  You have to
ponder this for a bit to realize that an internetwork call between two
networks with conflicting rules doesn't make the conflict visible to
either network!)

The DDN doesn't specifically claim to support passing CCITT-Specified
DTE facilities at this time, and I have no idea what would happen if
you tried to do it.  If it doesn't work now, it will probably be added
on the next pass.

Does it all make sense now?  Hmm, let me rephrase that.  Does it all
seem consistent now?

Bill Barns / MITRE-Washington / barns@gateway.mitre.org