Re: 100 Mbit/s is (a lot) slower than 10 Mbit/s

On Sat, Oct 19, 2002 at 09:08:04PM +0200, Harald Hanche-Olsen wrote:
> I have a Linksys ethernet card in my laptop.  It can to 10 or 100
> Mbit/s.  But when it's in 100 Mbit/s mode, transfers into the laptop
> are lots slower than at 10 Mbit/s, at least as long as the sender is
> on the same local net and has a 100 Mbit/s interface.
> 
> The reason is obvious enough: Snooping on the ethernet traffic reveals
> that packets are lost, with frequent timeouts and waits for
> retransmissions as a result.  The timeouts are easily visible by
> watching the blinkenlights on the dongle.  I am assuming this is a
> result of the Linksys' puny buffer being overrun, perhaps due to the
> bandwidth from the PCMCIA slot to the CPU not being big enough to
> cope.
> 
> So why don't I just use 10 Mbit/s then?  Well, at home that is what I
> do, since I can tell my stationary PC to run its interface at 10
> Mbit/s, and the Linksys will automatically follow suit.  But at work
> we recently upgraded our network to 100 Mbit/s, and hence the
> difficulty: The ed driver has no provision (it seems) for setting the
> speed.  (Maybe there is no way to ask the card to pick the lower
> speed.)
> 
> Could anyone suggest a reasonable workaround?  I though maybe I could
> set some kernel variables to make the window size in TCP smaller and
> hence stop the buffer overrun from happening so often, but I am not
> sure what knob to twiddle or even if there is one.  (Yes, recompiling
> the kernel is okay, too.)
> 
> Is this a common problem?  I don't see a lot of complaints about it on
> the list.  Maybe it's just the card that's crappy, and I should get
> another one?  FWIW, the card calls itself an EtherFast (ha!) 10/100 PC
> Card.  I got it back in 1999 because it was cheap, so I have got
> enough use out of it and won't be unduly upset if I need to scrap it.

Hi, perhaps this response is absolutely worthless, in which case I'd like to
ask you to silently ignore it. But: if your ethernet card is connected to a
switch, as opposed to a hub, did you check the duplex settings?

I know from personal experience that if your duplex settings don't match on
both the network card and the switch, packet loss will occur.

If you did, pretend I never sent this e-mail. ;-)

> - Harald
> 
> PS.  If the ethernet cable or dongle is disconnected for any reason,
> the laptop hangs until I lean on the power button.  Very annoying.

Can't comment on this one. Sorry. :(

-- 
Marco van Tol [mailto:[email protected]] [http://www.tols.org]

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