David Schleef <[EMAIL PROTECTED]> writes:
> I use tcpdump, and watch for duplicate lines, which means that the
> sender never recieved an acknowledgement for the chunk of data that
> was sent. You can get a feel for how this works by starting an ftp
> transfer between two computers while running tcpdump, and pulling
> the plug. (The network plug, not the power...) You should see
> the same packet being sent several times, at exponentially increasing
> intervals.
Thanks. I found tcpdump and looked at traces... However, it seems that
the problem is due to the slow sender (a P90 machine). I swapped the
sender and receiver (so that the sender is now a PPro200 machine) and
got delays of up to 0.3 seconds. It could be the time spent in
copying, I don't know...
> Even though it leads you down the dark path of "reinventing TCP",
> I would suggest switching to a UDP connection. One of the things
> UDP offers over TCP is that you can effectivly hog the network --
> TCP tries to be nice. TCP has a feature called "slow start", which
> makes it ramp up the bandwidth it tries to use. This can cause
> problems if you expect to be able to use a lot of bandwidth quickly.
I thought about this, but a friend, who has more experience with
the network configurations at my university, said that he had had too
many dropped packets when using UDP (around 90%). And I don't need
quick one-time connections, but just the opposite (periodic sending of
data, 225kBps on average).
> Actually, the particular NIC in the 3c59x series makes a difference.
> The output of 'dmesg' will tell you which it is. A "Vortex" card
> only has a 5 kB buffer, which can make it start dropping packets at
> an interrupt latency of 500 us. The "Boomerang" and "Cyclone" cards
> only handle 32 incoming packets at a time, which is probably not
> a problem. (Easy to check -- change RX_RING_SIZE in the source.)
It is a Boomerang... thanks for the info.
> dave...
Aleks
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