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Date: Sun, 8 Jun 2008 14:09:58 +0200 (CEST)
From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: Jon Radel <jon@radel.com>
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Cc: "Gelsema, P \(Patrick\) - FreeBSD" <freebsd@superhero.nl>,
	freebsd questions <freebsd-questions@freebsd.org>
Subject: Re: NFE setting manually to 1000baseT and half duplex
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> Even if you do have hardware that supports half-duplex gigabit ethernet
> on both ends, the need to do carrier extension for any frame shorter
> than 512 bytes so that CSMA/CD actually works on a reasonable sized
> cable, does horrible things to your throughput if you've got lots of
> small frames. (In other words, at gigabit speeds, frames smaller than
> 512 bytes zip down the wire so quickly that you can no longer reliably
> detect collisions, so the frames all get padded.) I'm having trouble wrapping 
> my head around any circumstances other than horribly, horribly broken 
> hardware or software where half-duplex would increase your performance over 
> full-duplex.

actually there are no gigabit devices incapable of full-duplex.
> ethernet hardware I've ever touched has been incapable of doing
> half-duplex when it's being used at gigabit speeds.  The specs for doing
> it exist more for theoretical completeness than out of practical
> utility.  See, for example
>
> http://www.intel.com/network/connectivity/resources/doc_library/white_papers/solutions/copper_guide/gig_over_copper.htm

at 10Gbit/s specs dropped half-duplex and collision detection at all.