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

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.

- 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.

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