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From: ast@botter.UUCP
Newsgroups: comp.dcom.lans,comp.protocols.misc
Subject: Re: OSI-model software
Message-ID: <1214@botter.cs.vu.nl>
Date: Wed, 17-Jun-87 06:26:47 EDT
Article-I.D.: botter.1214
Posted: Wed Jun 17 06:26:47 1987
Date-Received: Fri, 19-Jun-87 01:30:07 EDT
References: <223@diab.UUCP> <233@idacrd.UUCP> <526@alliant.UUCP>
Reply-To: ast@cs.vu.nl (Andy Tanenbaum)
Distribution: world
Organization: VU Informatica, Amsterdam
Lines: 31
Xref: utgpu comp.dcom.lans:490 comp.protocols.misc:56

In article <3002@pyramid.UUCP> sas@pyramid.UUCP (Scott Schoenthal) writes:
>I believe that Andy knows what he is talking about and I would certainly
>be interested if he would expand on the criticisms he mentions in his posting.

Ok.  For one thing, I think the session layer is ridiculous.  All it really
does is keep track of whose turn it is to talk and do some checkpointing.
I think most applications know whose turn it is to talk.  If I am addressing
an editor on a remote machine, we really don't need a whole layer to keep
track of whether I am allowed to type or it is the editor's turn to say
something.  In the British proposal to ISO years ago, there was no session
layer.  I think they were right.  The session layer was probably included
because IBM had one, and people must have assumed that if IBM did it, it
must be a good idea.  I am not convinced that there are enough applications
that use the session layer to make it worth having.   The ARPANET model
does not have any session layer and I have never heard of anyone saying he
needed it.

The presentation layer.  It is practically empty now.  All that seems to be
left is ASN.1 and ASN.2, which are several hundred pages of mumbo jumbo
for the purpose of telling which order the bytes are in (VAX, Intel = little
endian) vs. (68000, IBM 370 = big endian).  This seems overkill to me.

Encryption.  ISO seems to be totally unable to get its act together.  Other
than unambiguous statements that encryption does not belong in the session
layer or physical layer, it seems that all others are possible, although
lately I have been hearing noises that maybe presentation is "in" again.
I think spreading it out all over the place is a disaster.  Logically I
think it belongs in presentation--it deals with "meaning" in some sense.
In any event, the current situation is a disaster.

Andy Tanenbaum (ast@cs.vu..nl)