Radia Perlman (radia@XX.LCS.MIT.EDU)
Fri 20 Nov 87 10:03:14-EST
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.
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