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From: kre@munnari.UUCP
Newsgroups: comp.protocols.iso,comp.dcom.lans
Subject: Re: OSI-model software
Message-ID: <1709@munnari.oz>
Date: Sat, 20-Jun-87 09:32:06 EDT
Article-I.D.: munnari.1709
Posted: Sat Jun 20 09:32:06 1987
Date-Received: Sun, 21-Jun-87 06:55:01 EDT
References: <1204@botter.cs.vu.nl> <1680@munnari.oz> <192@ditmela.OZ> <1818@ames.UUCP>
Organization: Comp Sci, Melbourne Uni, Australia
Lines: 63
Keywords: osi, iso, internetworking
Xref: utgpu junk:5302 comp.dcom.lans:506

In article <1818@ames.UUCP>, lamaster@pioneer.arpa (Hugh LaMaster) writes:
> X.25 (level 3?) will, it seems, be used as an
> alternate "level 2.5" protocol.  Is 802.2 also considered "level 2.5"?
> Is there a draft standard on this yet?  What ISO number is it?

Here are a bunch of numbers ..

IS 8348		Network service definition
			(this says what you can expect the network
			layer to do for you, and if you're implementing
			any network protocol, what services you must provide).

IS 8348 AD 1	Network service definition addendum 1,
			Connectionless-mode transmission
				(ie: datagrams)

DP 8880		Specification of protocols to provice and support
			the OSI network service
			part 1: General principles
			part 2: provision and support of the connection-mode
					service
			part 3: provision and support of the connectionless-
					mode service

DIS 8878	Use of X.25 to provide the OSI connection-mode
			network service
				(this is what fills in the last .5 to
				turn the "2.5" layer X.25 into layer 3)

DIS 8208	X.25 packet level protocol for data terminal equipment
				(this is 1984 X.25)

DIS 8473	Protocol for providing the connectionless-mode
			network service  (see also also DAD 1, and PDAD 2).

DIS 8648	Internal organization of the Network Layer


There are other level 3 related protocols (DP 9542, "End system
to intermediate system routing exchange protocol for use in
conjunction with ISO 8473", and DP 9068, "Provision of the
connectionless network service using ISO 8208", are two that
might be relevant)

ISO 8802/2 (IEEE 802.2) is a link level protocol, as it provides only
point to point service (from one host, across a LAN, to another).
Contrary to what some others have implied, or even stated as fact,
ISO layer 3 is an *internetwork* protocol, with exactly the same
function in the overall scheme of things as IP has in the DARPA protocols.

In this are you might want to look at DIS 8881-1 "Use of the X.25
packet level protocol in local area networks, Part 1: use with LLC
Type 1 procedures" and DIS 8881-2 "... Part 2: use with LLC Type 2
pricedures".

While I'm rambling, I should also point out, that most people making
noises about IEEE 802.2 (8802/2) are considering only LLC Type 2,
which is the thing that looks a little like X.25 (or hdlc).  Remeber
that LLC Type 1 exists too, which is a protocol about as complex
as old form xerox/dec ethernet (and might go unnoticed because its
just a couple of pages in the 802.2 book).

Robert Elz			kre@munnari.oz.au