Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!cmcl2!nrl-cmf!ames!elroy!cit-vax!ucla-cs!zen!ucbvax!XX.LCS.MIT.EDU!radia
From: radia@XX.LCS.MIT.EDU (Radia Perlman)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Idle chatter about reference models
Message-ID: <12352127564.23.RADIA@XX.LCS.MIT.EDU>
Date: Fri, 20-Nov-87 10:03:14 EST
Article-I.D.: XX.12352127564.23.RADIA
Posted: Fri Nov 20 10:03:14 1987
Date-Received: Sun, 22-Nov-87 16:12:43 EST
References: <[A.ISI.EDU]19-Nov-87.10:28:05.CERF>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 17

The Network Layer in ISO already has lots of sublayers, with
catchy names like "Subnetwork Independent Convergence Protocol".
With hierarchical routing, there's really a Network Layer sublayer
dealing with each level of hierarchy.  When you (according to
ARPA terminology, I think) interconnect networks into an internetwork,
I'd say you're just forming another layer of hierarchy on your network.
That extra layer does involve adding a protocol layer onto what used
to be your Network Layer.  But it certainly doesn't go into
the Transport Layer.  It just makes your Network Layer fatter (makes
a Network Layer that used to have k sublayers now have k+1 sublayers.)

In general I agree that trying to take the ISO Reference Model too
seriously leads to nonproductive metaphysical discussions, but I don't
think hierarchical routing at the ISO Network layer breaks the model.

Radia
-------