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Date:      Wed, 9 Oct 1996 19:44:42 -0700 (PDT)
From:      "Rodney W. Grimes" <rgrimes@GndRsh.aac.dev.com>
To:        julian@whistle.com (Julian Elischer)
Cc:        jas@flyingfox.COM, John.McLaughlin@acucobol.ie, hardware@freebsd.org
Subject:   Re: Poor SMC Etherpower 10/100 transfer rates
Message-ID:  <199610100244.TAA08147@GndRsh.aac.dev.com>
In-Reply-To: <325C3D9B.446B9B3D@whistle.com> from Julian Elischer at "Oct 9, 96 05:04:43 pm"

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> Jim Shankland wrote:
> 
> > ballpark 3% of the theoretical maximum capacity); the FreeBSD
> > box is reporting a 20%+ collision rate!  I will now definitely
> > try swapping out the SMC card.
> 
> if it is reporting collisions then it's probably not teh culprit..
> it's the card that doesn't see ANY collisions thatyou should be 
> worried about.

Actually it does see the collisions, it is failing to listen to
the wire _before_ it transmits, but it sees the collision occur
just fine, backs off and then smashes the wire again without
seeing if it is busy :-(.  Generally just poke around and see
if other nodes are reporting collisions higher than expected tells
you that you have someone who is not listening before transmitting.

I have seen this on cards other than the DEC DC21x4x based ones, but
that has been some time ago.  This condition is often refered to has
``a balagerant mau'' and a common cause of it use to be thick ethernet
MAU's that had gone bad and where not driving the collision pair in
the AUI cable.  Since with 10BaseT wiring this is all on the card you
don't have a seperate MAU, perhaps this should now be called ``a
balagerant NIC'' :-).


-- 
Rod Grimes                                      rgrimes@gndrsh.aac.dev.com



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