Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!MIRSA.INRIA.FR!Christian.Huitema
From: Christian.Huitema@MIRSA.INRIA.FR
Newsgroups: comp.protocols.iso
Subject: Re: X-WINDOWS & OSI
Message-ID: <8906131330.AA26514@jerry>
Date: 13 Jun 89 13:30:42 GMT
References: <8906061752.AA01135@emu.ncsl.nist.gov>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 35

There is currently a proposal on the table, by DEC, using a full suite,
including ACSE and presentation over a full duplex session. To sum it up:

* ACSE is used for connection management operations, e.g. open window
or kill window;

* X-window protocol items are carried as octet strings in an
``unstructured octet string'' presentation context.

This proposal has several advantages over the short sighted approach of
``just using the transport service'':

* it is fully conforming to the architecture,
 
* as a consequence, the client part could be easily implemented on
those systems which provide T & S ``as a single package'', e.g. IBM OSI
offers for mainframes,

* using the presentation service allows for the packing of several
X-requests in a single S (or T) message, which has significant performance benefits.

It is untrue to assert that the use of S + P ``must cost millions of
instruction''. In fact, by taking advantage of the limited number of
session services that can be negociated, it would be possible to
implement the session in an X server with very minimal overhead, e.g.
half a dozen instructions.

I have some reservations on this approach, though. In my opinion, it is
somewhat too ``minimalist'', and a real ``OSI X-Window'' should include
a proper definition of the X protocol in the ASN-1 language; however, I
realize that the time to develop + demonstrate such a tool could be a
bit long, and that its advantages have to be weighted against achieving
an ANSI (then ISO) standard in a short time frame.

Christian Huitema