Re: Does TCP/IP "comform" to ISO/OSI?


Michael Padlipsky (PADLIPSKY@A.ISI.EDU)
Tue 6 Sep 88 16:23:21-EDT


Philip--

Many thanks for the great straight-line (which came at a particularly
good time, since I'm enjoying a temporary remission from the smoking-ban-
engendered chemical lobotomy at the moment, owing to the finally decent
weather where I am, which means I don't come back in from taking the
medication of choice for my condition more tired than when I went out,
for a delightful change).

How do _I_ think X.25 "stacks up" against the ISORM _aesthetically_, you
ask? I don't. I think it throws up.

Turning from the aesthetic to the technical, you do seem to me to be on
the right track in noting that the "D" bit is rather L4-ish, or at least
not very L3-ish. The other alphabits (M and Q, as I recall) are also
hard to swallow. Indeed, despite the ISORM's stated precept that protocols
must be peer to peer, the D bit seems to allow a given Host ("DTE") X.25
protocol interpreter to interact with the remote Comm Subnet Processor
("DCE") X.25 PI, the M and Q bits allow it to interact with the remote
Host/DTE X.25 PI, and most of everything else allows/requires it to interact
with the proximate CSNP/DCE's X.25 PI--always assuming I've remembered
aright which is DTE and which DCE. That situation, as I've observed in
passing elsewhere, sure looks like a POLY-PEER to me.

So there's no need to get into any lawyering over whether X._7_5 is or
isn't "Open", or to dredge up any of the other X.25-X.75 inelegancies,
to conclude that X.25 does not instantiate ISORM principles at all
scrupulously. The poly-peerage alone is evidence enough. (More
technoaesthetic points on the topic can be found in RFC 874, or even
in Chapter 9 of _The Elements of Networking Style_, where you not only
get the Cover Cartoon and Prefatory Afterthoughts that don't come with
the RFC, but you'll also get a useful suggestion as to how to visualize
a poly-peer that I really shouldn't mention in "public".)

Nor should the disparity be surprizing, viewed historically. To the
best of my knowledge, belief, and personal recollection, the claims that
X.25 "is" ISORM L3-1 were advanced eight or so years ago by the ISORMites
(i.e., those panacea pedlars whose "ricebowl" was going to be the ISORM--
not to be confused with the ISORMists, who, even if I find them to be
backing the wrong horse [or the wrong end of the horse, if you prefer], do
seem to be trying to work within the international standards bodies to do
networking rather than ricebowl-gilding). The idea was to support their
claim that the ISORM Suite was "nearly here" by pointing to the "already
here" L3-1. (They did, as a matter of fact, have me fooled for a year
or two.) The key fact is that the ISORM is the product of the International
Standards Organization, whereas the X.25 stuff comes from CCITT, an entirely
different body which consists of representatives of "the PTTs" (or Postal,
Telephone, and Telegraph state monopolies [in most parts of the world]).

More some other time. I must go raise my norepinephrine levels now.
Perhaps somebody else can take up the tale of how ISO and CCITT currently
stand in their attempts to reconcile the ISORM and X.25; all I "know"
about it is that some ISORMist friends told me a year or three ago that
it had been deemed politcially desirable to (appear to, at least) do so.

   grateful cheers, map
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