Path: utzoo!attcan!uunet!zaphod.mps.ohio-state.edu!ncar!boulder!bobk
From: bobk@boulder.Colorado.EDU (Robert Kinne)
Newsgroups: comp.protocols.iso
Subject: Re: Question on the OSI 7 layer model?
Message-ID: <28843@boulder.Colorado.EDU>
Date: 29 Oct 90 04:51:00 GMT
References: <9905@milton.u.washington.edu>
Sender: news@boulder.Colorado.EDU
Reply-To: bobk@boulder.Colorado.EDU (Robert Kinne)
Organization: University of Colorado, Boulder
Lines: 34

In article <9905@milton.u.washington.edu> ski2@milton.u.washington.edu (Chris Kacoroski) writes:
>Hi,
>
>I have two references on the OSI 7 layer model that disagree on what
>the model does in the applications layer.  The analogy is that of
>sending a letter from the US to Germany.  Reference 1 from 1987 states
>that the OSI model will not only send the letter but will also
>translate its contents from English to German.  Reference 2 from 1989
>states that the OSI model will only send the letter and not affect the
>contents at all.  The method in reference 2 is akin to the current
>postal system.  My question is: Which reference is correct?  

First, understand that the OSI model is exactly that; a model that
breaks the communication process into seven defined layers, with
layer interfaces and some concept of peer-to-peer level exchange.
So the OSI model doesn't deal with the kind of issue you raise, but
specifications of the layers and interfaces do.

Second, the analogy of a 7-layer communication to a letter in the
post is a loose one, and shouldn't be taken too literally.

Third, the issue you raise is not an application layer question,
but properly a presentation (layer 6) question.  The purpose of
the presentation layer (simplified, of course) is to place the
communication into a form (code, language, syntax, whatever) that
will be understood by the application layer.  In the analogy of a
letter (keeping the second point in mind), if you speak only German,
the letter would be presented to you in German translation, since
your presentation layer would 'know' that you don't understand
English.
>
>Also, how does the MAP/TOP effort deal with the above problem.  Does
MAP/TOP hasn't evoloved to deal in any detail with presentation
layer as yet.