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From: chuck@amdahl.UUCP
Newsgroups: comp.dcom.lans
Subject: Re: OSI-model software
Message-ID: <8613@amdahl.amdahl.com>
Date: Mon, 15-Jun-87 16:35:04 EDT
Article-I.D.: amdahl.8613
Posted: Mon Jun 15 16:35:04 1987
Date-Received: Wed, 17-Jun-87 02:09:53 EDT
References: <1204@botter.cs.vu.nl> <1680@munnari.oz> <192@ditmela.OZ> <920@bloom-beacon.MIT.EDU>
Reply-To: chuck@amdahl.UUCP (Charles Simmons)
Organization: Amdahl Corp, Sunnyvale CA
Lines: 21
Keywords: osi, iso, internetworking

In article <920@bloom-beacon.MIT.EDU> martillo@athena.mit.edu (Yakim Martillo) writes:
>IEEE 802.2 and ISO level 2 puzzle me as well.  These are protocols for
>the communications subnet and I don't quite understand why IEEE and
>ISO are trying to define communications subnet protocols for all time.
>Shouldn't communications subnet protocols be medium-dependent?

Actually, if you look closely at 802.2, you'll notice that the IEEE
defines an interface within the datalink layer.  802.2 defines
the logical link control layer, and is, and should be, medium-independent.
Underneath the logical link control layer there exists a medium
access control layer which is, naturally, highly medium-dependent.

The advantage to this approach, of course, is that the MAC layer
is extremely simple, while the LLC layer is relatively complex.
Making the LLC layer hardware independent makes it easier to port
LLC layers from one machine to another.  The MAC layer must be
written anew for each machine and for each type of wire attached
to the machine, but since it is relatively simple, this porting
cost is not great.

-- Chuck