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From: mccallum@opus.UUCP (Doug McCallum)
Newsgroups: net.lan
Subject: Re: ISO Class 4 - what is it?
Message-ID: <1215@opus.UUCP>
Date: Fri, 24-May-85 10:37:14 EDT
Article-I.D.: opus.1215
Posted: Fri May 24 10:37:14 1985
Date-Received: Mon, 27-May-85 06:59:37 EDT
References: <1302@ecsvax.UUCP>
Organization: NBI,Inc, Boulder CO
Lines: 40

> I'm a little confused by the use of the term "ISO Transport Class 4 protocol".
> Just what is meant by "Class 4"?  Is that really layer 4?  Does the ISO
> layer 4 protocol have a nice acronym like DoD's TCP?
> 
> 				David Hinnant
> 				SCI Systems, Inc.
> 				...!{akgua,decvax}mcnc!ecsvax!dfh
> 				or ...!{akgua,decvax}mcnc!rti-sel!scirtp!dfh

ISO Transport Class 4 is a particular version of the ISO transport layer.
There are currently 5 classes of transport:
	Class 0:	Simple Class
			This is a minimum functionality class which provides
			the minimum functions for connection and data transport.
			It assumes a fairly reliable network with acceptable
			error rates.
	Class 1:	Basic Error Recovery Class
			This class provides a basic transport connection with
			minimal overhead.  It also assumes a reliable network
			but can recover from disconnects or resets.
	Class 2:	Multiplexing Class
			This class allows multiplexing multiple transport
			connections onto a single network connection.  It
			assumes the same type of network as Class 0.
	Class 3:	Error Recover and Multiplexing Class
			Same as Class 2 but recovers from errors indicated
			by the network layer.  This assumes a network of the
			same type as Class 1.
	Class 4:	Error Detection and Recovery Class
			This is the class that deals with detecting errors
			as well as recovering.  It assumes the worst case
			about the network.  Similar to TCP in this respect.
	
	There is a lot more detail that I've left out, but this covers the 
	basics.  ISO DIS (Draft International Standard) 8073 describes these
	classes more fully.  On the ARPANET, RFC 905 is a version of DIS 8073.

			Doug McCallum
			NBI, Inc.
			{allegra, ucbvax, ut-sally}!nbires!mccallum