Messages in this thread | | | Date | Fri, 16 Feb 2001 11:15:51 +0000 (GMT) | From | James Sutherland <> | Subject | Re: 8139 full duplex? |
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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 wasn't...
> 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...)
James.
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