Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!decwrl!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.dcom.lans
Subject: Re: FDDI Performance
Message-ID: <84440@sgi.sgi.com>
Date: 7 Feb 91 17:27:32 GMT
References: <1991Feb1.175751.13639@relay.nswc.navy.mil> <7185@titcce.cc.titech.ac.jp>
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Organization: Silicon Graphics, Inc., Mountain View, CA
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In article <7185@titcce.cc.titech.ac.jp>, mohta@necom830.cc.titech.ac.jp (Masataka Ohta) writes:
> ...
> For writing, according to the NFS specification, writing must be somewhat
> synchronous, so forget about caching.

There is controversy on this subject.  At least two system vendors and at
least one add-in-hardware vendor offer optional server cache mechanisms.

> >Is the UDP speed quoted above the value reported by the transimitter or by
> >the receiver?
> 
> Of course, 40Mbps is observed on both side. I know what is UDP.
> 
> I can understand that the figure has astonished you. But, please,
> don't assume I am an idiot and make a rather lengthy post. You could
> have used mail.

The reported numbers are respectable, but far from "astonishing."
I know of more than one independent implementation that gets several times
the ttcp TCP value.  The NFS value of 1-2 MByte or 8-16 Mbit sounds like the
systems are disk limited.  The 40Mbit ttcp UDP value is excellent, but not
unheard of.  I'll guess that the low 10Mbit TCP value, esp. compared to the
40Mbit UDP value, is caused by using a small window or MSS.  The latter can
occur with routers (not the fault of the routers, of course.).

Observing the same value on transmitter and receiver is surprising.  It
suggests that the tested implementation is transmitter limited.  That is
surprising given MIPS style caching.  (Measurements in such a realm is a
popular pastime around here.)

Please accept my appologies if my previous message implied I consider you
an "idiot."  I do not know you well enough to have any opinion on your
competance.  It is a fact that many people paid to work on this stuff do
not understand UDP, not to mention TCP.  The development mangers and VP
from the ethernet board maker with the 12Mbit/sec UDP/ether performance
that I wrote about previously were not joking and not idiots.  They were
trying for a long term contract with a major workstation maker.


Vernon Schryver,  vjs@sgi.com