[Soekris] Strange problem with net4801

Horst Laschinsky horst.laschinsky at physik.uni-erlangen.de
Tue Jan 18 01:27:23 UTC 2005


Hallo list

I am currently dealing with a strange problem concerning the net4801
board. The board is connected to another PC via a twisted pair cross
link cable. The NIC in the Soekris board as well as that in the PC
are set to 100 Mbit, full duplex. Both systems run Linux.
When I try to transmit data from the Soekris to the PC over tftp (or
any other simple file transfer protocol) I get transfer rates of
about 1 MByte/s which is about a factor of ten too low compared to
the speed of the connection. But what is even odder: if I do the
file transfer via scp, I have transfer rates of about 10 - 50 _kilo_
bytes and lots of carrier errors (about 2/3 of the packets cause a
a carrier error)!
If I transmit data from the PC to the Soekris, I get 1 MByte/s, no
matter if I use tftp or scp.
If I transmit data from the Soekris to itself (scp to localhost)
I have full speed, only limited by the disk speed.

I simply do not understand:
 
1) Why is the transfer rate so small at all? Maybe interrupt / DMA
   conflicts?
2) How can the application layer protocol have influence on the phy-
   sical layer???
3) Why does 2) only apply to outbound connections?

The Soekris runs a standard Debian installation with Kernel 2.4.27
(vanilla). The PC currently runs SuSE 9.2, but the problem also ex-
ists, if I connect the Soekris to other computers, running Linux or
Windows or whatever. I also tried to replace the cross link cable,
which had no effect. Netfilter is disabled on both sides (all three
default chaines are set to ACCEPT).
The data to transmit is stored on a 2.5" hard disk, but the effect
still remains, if I copy the data to a compact flash card and try to
transfer it from this device to the PC.

Does anyone of you have an idea or, even better, a solution?

Best regards,

Horst

-- 
                             Horst  Laschinsky
        Universitaet Erlangen-Nuernberg - Physikalisches Institut I
 Erwin-Rommel-Str. 1, Room: 207, 91058 Erlangen - Tel: ++49 9131 85-27076
       http://www.antares.physik.uni-erlangen.de/~htlaschi/index.php



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