Half/full duplex

[Jens Schliephacke]

Hi Stavros!
I'm not sure if I can help, but I have run some test with half/full
duplex with two linux boxes.
First of all: I think the autodetection only detects the mode at
bootup/module load, so you have to reboot both machines.

I have tested the following:
ftp transfer with GET from B to A of a 50MB file.
linuxA has 128MB RAM, linuxB 80MB, so the 50MB file is fully received
from cache.
The cards and driver are: 3c59x.c:v0.99E
eth1: 3Com 3c905 Boomerang 100baseTx

There are two configurations:
X: linuxA - cable - hub - cable - linuxB (should be half duplex)
Y: linuxA - crossovercable - linuxB (should be fullduplex)

The results:
1) X, both rebooted:	2,5 e+03 kB/s
   then simply switch cables to
2) Y, no reboot:	2,5 e+03 kB/s
   then
3) Y, both rebooted:	1,1 e+04 kB/s
   then simply switch cables to
4) X, no reboot:	canceled because of tooo slow.

Under 1) the hub-collision LED blinked a lot, activity was high.
Under 4) the hub-collision LED was constantly lit, activity was low.

So, there is a huge difference noticable between full/half duplex.
I don't know what happens if you boot your machines without a connection
and later plug in the cable. I guess as David stated it will be by
default in half duplex mode.

Jens.