Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!AHWAHNEE.STANFORD.EDU!dcrocker
From: dcrocker@AHWAHNEE.STANFORD.EDU (Dave Crocker)
Newsgroups: comp.protocols.iso
Subject: Re: TCP/IP versus OSI
Message-ID: <8905160042.AA12996@ucbvax.Berkeley.EDU>
Date: 15 May 89 16:09:31 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 61

Bob,

I think that you may be importing too much functionality to the TSB and
that you may want to use it in some ways that could be better done in other
ways...

You cite three situations.  The first has OSI, down to CLNP, running in
an IP network.  You put in a TSB to allow CLNP to run over OSI Transport
and then have it translated to run over TCP.  This sounds strange, to say
the least.  Running CLNP encapsulated over IP, directly, where CLNP views
IP as a link-level protocol, is far cleaner.

The second situation reverses the relationships, to have IP running over
a CLNP network.  Again, the solution is far cleaner to have IP view CLNP
as a link protocol and CLNP think that IP is a Transport protocol.  I do
not see any benefits of placing TSB-like technology in between and, in fact,
it does not sound as if it would work.

Your last scenario uses a TSB to map OSI, down to CLNP, over to OSI, down
to session, over RFC1006 and IP.  (ISODE only goes down to session.)
This truly does not compute.

A rule for determining how/when/where to do conversions:  Create two
protocol stacks. Look for the highest and lowest points of departure.
You need to translate in between those points, at the highest level.

e.g.,

OSI APPl       TCP APPL
...            ...


Means that nothing is in common and you translate above it; i.e., an
applicatio gateway.

OSI APPL       OSI APPL
OSI PRES       OSI PRES
OSI SESS       OSI SESS
OSI TPORT      TCP
...            ...

Means that you need to translate at transport level.  This is the exact, and
only, case that the documented Transport Service Bridge will solve.  To the
extent that the other scenarios you describe can and should be done, they
are independent of this particular kind of TSB.  I.e., they are different
products.

ANother example:

OSI APPL/ROSE   OSI APPL/ROSE
OSI PRES        
OSI SESS
OSI TPORT       TCP
...             ...

The right-hand column is what is being called "light-weight presentation"
and is what Marshall did for the NetMan CMIP-over-TCP group.  To interwork
with the pure OSI world, this requires a ROSB (Remote Operations Service
Bridge).

Dave