Date: Sat, 19 Oct 2002 21:08:04 +0200 From: Harald Hanche-Olsen <hanche@math.ntnu.no> To: freebsd-mobile@FreeBSD.ORG Subject: 100 Mbit/s is (a lot) slower than 10 Mbit/s Message-ID: <20021019210804P.hanche@math.ntnu.no>
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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. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-mobile" in the body of the message
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