Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!usc!bbn!bbn.com!craig
From: craig@bbn.com (Craig Partridge)
Newsgroups: comp.protocols.misc
Subject: Re: A comparison of Commercial RPC Systems
Message-ID: <43535@bbn.COM>
Date: 31 Jul 89 16:27:33 GMT
References: <6569@joshua.athertn.Atherton.COM> <449d9c67.12879@apollo.COM> <118603@sun.Eng.Sun.COM>
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In article <118603@sun.Eng.Sun.COM> beepy%commuter@Sun.COM (Brian Pawlowski) writes:
>I have to object to the term "in general". I would respond that "in general,
>the use of 8K UDP datagrams is a win for transferring large amounts
>of data, and has shown to be a win in applications such as NFS."

I think this argument about "in general" is missing the key point.
Fragmentation is known not be robust -- see Mogul and Kent's article
on this in 1987 Proceedings of SIGCOMM.  The basic rule is that *if you rely
on fragmentation to work you are building protocols that are guaranteed
to fail in many common situations.*  Indeed, this is why many of us
were pleased to see Sun experiment with methods for dynamically determining
the transmission unit size for NFS (see Bill Nowicki's article in the April '89
issue of ACM SIGCOMM Computer Communication Review).

>I like your argument, EXCEPT FOR THE FACT THAT IT FLIES IN THE FACE
>OF WHAT WE SEE IN LARGE nfs NETWORK INSTALLATIONS. I think you are
>approaching this from a pessimistic, worst case scenario which is
>a bad way to deal with network throughput. In general, I have to assure
>you - it works.

This is a poor counter argument.  Saying "we haven't seen problems"
when there are demonstrable research results that show you will have
problems in certain situations is an ostrich approach.  It leads to
cruddy protocols.

Craig

PS: I understand that there's an element of SUN vs. Apollo protocols here.
All I'm asking is let's stick with agreed upon basic principles of network
protocol design in the debate -- one such principle is that fragmentation is
a bad idea.