Vernon Schryver <vjs@calcite.rhyolite.com> Fri, 09 August 1996 06:19 UTC

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Date: Thu, 8 Aug 1996 22:35:35 -0600 (MDT)
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From: Vernon Schryver <vjs@calcite.rhyolite.com>
Message-Id: <199608090435.WAA29105@calcite.rhyolite.com>
To: Big-Internet@munnari.oz.au
Subject: FDDI MTU
Precedence: bulk

> Well, 4470 is the common FDDI and HSSI MTU, and so that's a pretty common 
> one for high-speed links...

See RFC 1390 and its predecessors to discover that the IP MTU for FDDI
has been 4352 for a long time.  I can't guess the source of 4470, since
the maximum total frame FDDI size is about 4500 bytes.  ("about" because
of the indicators after the FCS).

> box" solutions.  Reports from the field are that a "100Mbps" network 
> on which a PCI Pentium is sourcing or sinking traffic can not really expect 
> to see more than about 50Mbps due to the packet processing overhead in 
> this environment with a 1500 byte MTU -- but that number rises to nearly
> 85Mbps with a 4470 MTU.

That is not consistent with the 80 Mbit/sec netperf number
(http://www.cup.hp.com/netperf/NetperfPage.html) for 100BASE-T for
a "Noname Pentium 1".  (Of course, 100BASE-T uses an MTU of 1500.)

Vernon Schryver    vjs@rhyolite.com