Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!brutus.cs.uiuc.edu!zweig
From: zweig@brutus.cs.uiuc.edu (Johnny Zweig)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: more on Fletcher
Message-ID: <1989Dec7.203820.1337@brutus.cs.uiuc.edu>
Date: 7 Dec 89 20:38:20 GMT
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I don't know why this talk about intelligent communications processors seems
to be taken for granted -- I was thinking of using Fletcher checksumming on
Mac's with potentially flakey 3rd-party ethernet interfaces, other
workstations and minis without front-end TCP/IP processors.  I'll grant
that if a front-end can't communicate reliably with a host, that's that
and it's time to change hardware.

Let me quickly respond to several of the arguments I've seen (paraphrased):

	The current checksum is fine. Don't change it.

I am not suggesting anyone change anything, nor would I hope for such a thing.
I want to add the possibility of a few lunatic-fringe people who feel it
might be necessary/fun/worth looking at to use alternate checksum techniques.
An argument that says the current way of doing things is fine is looking
at what I suggested wrong.

	The End-To-End argument is wrong; concatenation of reliable links
	is all you need.

Fine. I assert that, on my Mac, the linke between the ethernet card's RAM and
my system RAM is unreliable, so I want to make the TCP module running on
it sufficiently robust to detect failure of that link.  I am glad you agree
(albeit implicitly) that an alternate checksum capability is necessary to
make this last (and vital) link reliable, since the end-to-end argument and
the link-by-link argument agree on what to do when what you're talking
about the last link.  (Hairsplitting: the ethernet-card -> TCP link is the
last hardware link, not the last conceptual link since the data still needs
to be copied reliably to the application.)

	Water is wet and I don't get paid to listen to malcontents who
	want to make my life more complicated.

I apologize. It's in my nature.


-Johnny