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From: kre@cs.mu.oz.au (Robert Elz)
Newsgroups: comp.protocols.iso
Subject: Re: OSI IP routing on the DDN?
Message-ID: <1444@murtoa.cs.mu.oz.au>
Date: 29 Apr 89 19:49:47 GMT
References: <8904281658.AA00796@ucbvax.Berkeley.EDU> <8904282330.AA29812@hpinddm.HP.COM>
Sender: news@cs.mu.oz.au
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In article <8904282330.AA29812@hpinddm.HP.COM>, kmont%hpinddm@HP-SDE.SDE.HP.COM (Kevin Montgomery) writes:
> 
> My point was that you couldn't build a single 
> network layer (with only one NSAP/IP address) to handle both types 
> (ISO and ARPA) transparently to the upper layers (either ISO or TCP).  

But why would one want to?   One of the standard requirements of any
lower level protocol is that it provide protocol differentiation for
higher layer protocols layered upon it.  That's used all the time.

Consider how you would differentiate TCP UDP ICMP (etc) if you weren't
allowed to look at the IP header (that is, if there was none).

Those protocols use a protocol IS in the IP header, IP (and ISO IP, etc)
use protocol ID provided in the next lower level (ethernet, X.25,
whatever).   1822 is going to be a problem, but that's on the way out
isn't it?

kre