Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!ucbvax!decwrl!decvax!jfcl.dec.com!frg
From: frg@jfcl.dec.com (Fred R. Goldstein)
Newsgroups: comp.protocols.iso
Subject: Re: OSI CLNS and the future of networking
Message-ID: <360@jfcl.dec.com>
Date: 23 May 88 19:23:02 GMT
References: <1097@ditmela.oz>
Reply-To: frg@jfcl.UUCP (Fred R. Goldstein)
Organization: Digital Equipment Corporation
Lines: 42

In article <1097@ditmela.oz> smart@ditmela.oz.au (Robert Smart) writes:
>The OSI CLNS (ConnectionLess Network Service) is basically just 
>DoD's IP with minor changes (like a bigger address field). The 
   Well, not exactly... but they're rather similar.  Note, though,
that the proper terminology is that OSI IP (ISO 8473) is the 
protocol which implements the OSI CLNS (service description in
ISO 8348/AD1.  In the OSI world, services and protocols are 
usually described separately.

>That's all very well, but I would like to understand how CLNS over 
>X.25 coexists with the existing CONS (ConnectionOriented Network 
>Service) over X.25. I guess they just use different Subaddress or 
>Protocol-id or Call User Data. I am also not sure how CLNS over
>802.3 fits in with existing OSI over 802.3. Presumably the packets
>will have CLNS sender and destination addresses in them (the new IP
>addresses). That certainly isn't what is in them now. 

X.25-1984 provides the CONS, and is equal to ISO8208.  Of course
X.25 uses X.121 addresses and CONS allows the address to be the
"long form" in ISO8348/AD2.

ISO IP (CLNS provider) can run on top of X.25 or 802.3 or, for
that matter, practically anything else.  The procedure for using
X.25 (called a Subnetwork Dependent Convergence Protocol) is
within the text of ISO 8473.  The IP (CLNS) packet sits inside
an X.25 packet.

This is just an example of the structure of the Network Layer,
which is not one protocol but in practice, potentially a stack
of "roles".  Whatever the transport layer sees (the Network Service)
is provided by the top Subnetwork Independent Convergence Protocol.
(Sometimes called an Internet protocol, esepcially if connectioneless!)
Whatever the underlying comms medium provides (wire, Ethernet, X.25,
CONS, LAP-D, etc.) is the Subnetwork.  Whatever has to go in between
them to make the SNICP work is the SNDCP.  Put 'em together right
and you can make all sorts of combinations play.  Not all with
equal efficiency, though!
>
>Bob Smart, CSIRO Division of Information Technology, Australia
       fred
-- 
usual disclaimers apply