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Path: utzoo!mnetor!seismo!sundc!hadron!cos!howard
From: howard@COS.COM (Howard C. Berkowitz)
Newsgroups: comp.dcom.lans
Subject: Re: OSI-model software
Message-ID: <331@cos.COM>
Date: Fri, 19-Jun-87 08:55:19 EDT
Article-I.D.: cos.331
Posted: Fri Jun 19 08:55:19 1987
Date-Received: Mon, 22-Jun-87 01:54:18 EDT
References: <1204@botter.cs.vu.nl> <1680@munnari.oz> <192@ditmela.OZ> <1818@ames.UUCP>
Organization: Corporation for Open Systems, McLean, VA
Lines: 34
Keywords: osi, iso, internetworking
Summary: 802.3 = Draft International Standard 8802/2

In article <1818@ames.UUCP>, lamaster@pioneer.arpa (Hugh LaMaster) writes:
> In article <1800@ames.UUCP> lamaster@pioneer.UUCP (Hugh LaMaster) writes:
> 
> It seems that I have mixed it up; I have received several replies to that
> effect.  My apologies.  X.25 (level 3?) will, it seems, be used as an
> alternate "level 2.5" protocol. 

A fine distinction here:  OSI has "layers;" X.25 has "levels."
X.25 Level 3 = OSI Layer "2.5" (more or less).  The 1984 version
of X.25 has several extensions for greater OSI compatibility,
including the ability to extend addresses from the X.121 14-digit
maximum to the 32-digit maximum of the OSI Network Service.

> Is 802.2 also considered "level 2.5"?

802.2 has several classes of operation.  The simplest, Class 1,
is connectionless and offers no error correction.  This class
has been adopted by the NBS Workshop for OSI Implementors:
"Only the connectionless type 1, class 1, IEEE 802 service
will be used."  COS and MAP/TOP also use class 1 only.

802.2 Class 1 has very minimal functionality, and basically
serves the implementation role of insulating Layer 3 from
the timing and buffer issues of the MAC sublayer of Layer 2.
As a minimal protocol, it is much less than X.25, and thus
is considered pure Layer 2 (Logical Link Control -- LLC -- sublayer).

NBS, COS, and MAP/TOP all assume Internet on top of LLC1.

> Is there a draft standard on this yet?  What ISO number is it?

So far, all standards out of the 802 Project have been given
"derivative" international numbers:  802.X = ISO 8802/X.
For example, 802.3 is ISO 8802/3.