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    SubjectRe: 8139 full duplex?
    On Fri, 16 Feb 2001, Rogier Wolff wrote:

    > James Sutherland wrote:
    > > > That would explain me seeing way too many collisions on that old hub
    > > > (which obviously doesn't support full-duplex).
    > >
    > > No, it would just prevent your card working. Large numbers of collisions
    > > are normal during fast transfers across a hub.
    > Why would it completely "not work"?

    It wouldn't be able to detect collisions, I suspect; you might be able to
    get data through, though. Not something I've ever wanted to try :-)

    > As long as the host doesn't have something to send while a recieve is
    > in progress, everything should work. A friend reports that he spent
    > lots of time trying to debug a network where "too many" collisions
    > were happening. Turns out one card was in full-duplex, while the other
    > side wasn't.

    On a crossover cable direct between two machines, that would make sense:
    you would WANT both cards full duplex, but if one ran half duplex instead,
    it would think it was getting a huge number of collisions when it

    > I benchmarked my old network at 10-12 seconds for a 100Mb
    > transfer. That sounds indeed as if there isn't a whole lot of
    > collisions happening. And I can immagine that the acks run into the
    > next data-packet all the time, so that performance would indeed be
    > very bad if the card was misconfigured. On the other hand I had one
    > machine that was taking 180 seconds for the 100Mb transfer.

    Ouch! Remember each collision only knocks out a few hundred bytes -
    perhaps 1.5K - so even hundreds of collisions per second only knock a few
    hundred K/sec off a transfer rate of ten Mbyte/sec or so.

    > Anyway, I remember fiddling with the eexpress 100 driver, and there
    > the driver was involved in switching the speeds, and doing some
    > management of the switchover of full-duplex/half-duplex. I'd expect
    > some message from the driver if it saw such a change.
    > But you're saying that the 8139 chip does it internally, and fully
    > automatically? Ok. Good.

    Well, mine do anyway :-)

    (Except under the Win2k bug, where I needed to force the link to 100
    Mbit/sec full duplex...)


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