[Soekris] Strange problem with net4801

Horst Laschinsky horst.laschinsky at physik.uni-erlangen.de
Wed Jan 19 01:55:20 UTC 2005

Clemens Zauner wrote:

> Do not use cables with shielding on both sides. either unshielded,
> or shield connected to ground on only one end.

What the f...? That worked! Can anyone explain me why? Up to now,
I always thought the sole reason for the existance of common grounds
was to _avoid_ disturbances???

But anyway, this still does not explain the effect as such.

> > 1) Why is the transfer rate so small at all? Maybe interrupt / DMA
> >    conflicts?
> The 4801 has a 233MHz CPU. you will experience some limitations here.

Of course I may. But is a 233MHz CPU really so slow, that it cannot
transfer data at 100MBit (or at least 40-50 MBit) 3des encrypted?
> Usually not, But as you are running 1 stream you will see some effects.
> e.g. Collisions are unlikely if you do only tftf (udp-bound protocol);
> as the server sends out udp frames and the clients ACKs them (and
> the server does not send any more until the ACK is received => the medium
> is idle).

Yes, this would result in packet drops or other errors. But what
I got was a "carrier error", and that means that the NIC lost the
link beat. And I simply cannot explain how the ssh protocol could
cause this!

> > 3) Why does 2) only apply to outbound connections?
> One side is sending ACKs (small packets), the other data (large).

Yes, but if I transmit data from the PC to the Soekris it would be
just the other way round. So the effect should also appear but
it doesn't.

Anyway, thank you very much!


                             Horst  Laschinsky
        Universitaet Erlangen-Nuernberg - Physikalisches Institut I
 Erwin-Rommel-Str. 1, Room: 207, 91058 Erlangen - Tel: ++49 9131 85-27076

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