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FDDI MTU

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Vernon Schryver

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Aug 8, 1996, 3:00:00 AM8/8/96

to id fa15785, fri

> 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 v...@rhyolite.com

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