[wellylug] Dummy ethernet crossover?

[Eugene Van Wyk]

Hi all

I tried something like that recently and had the same issues.  Looking
at things with an oscilloscope showed short pulses running between my
board and a hub/switch - I do not remember what I had on the other end.
I could not detect any DC offset, which was my first guess based on coax
type networks.  
I could also never quite figure which side originates the pulse.

I would greatly like to find out what happens at the electrical level,
but have so far not been able to source some solid info.  

I am currently just using a switch to do what I need to, but then my
solution doesn't need to be portable.

To add to this mystery, I have a relay bank between my 4 port device,
and the network switch.  To test the various ports I do tftp file
transfers between the network switch and my board, and switch the
connected port (on my board) via the relay bank after every tftp file
transfer.  That all works fine.

My relay bank only switches the 2 active pairs.  However, if I make up
cable jumpers between my relay bank and the network gear, I have to use
a standard cable.  I tried making up the short interconnects using only
2 pairs of cable, which kill my network transactions.??  I have not
found anybody that can explain this one either.  Any wise LUG'rs out
there?

Eugene van Wyk
Test Development Engineer
4RF Communications Ltd
26 Glover St
Ngauranga
Wellington
New  Zealand
 

-----Original Message-----
From: wellylug-admin at lists.wellylug.org.nz
[mailto:wellylug-admin at lists.wellylug.org.nz] On Behalf Of Edmund A.
Hintz
Sent: Tuesday, 28 September 2004 5:07 p.m.
To: Wellylug
Subject: [wellylug] Dummy ethernet crossover?

Hi all...

    I've got a bit of an oddball problem here... I need to fool an
ethernet interface into thinking it's up (it's a long story, just trust
me that I need to do this). I tried doing a crossover cable of sorts by
snipping a cat5 cable, stripping the plastic, and twisting together 1-3
and 2-6. Doesn't work. I'm guessing I need some sort of capacitor or
something in the loop, but all I can find on google is xover cables
(great, but there's only 1 enet interface in the loop so it's useless).
Anybody know where I need to look to find a solution?

    As things stand now, I can plug the machine into a switch, with
nothing else plugged into said switch, and it does what I need it to do
(virtual machines talking to each other). But I'd like to find a more
portable solution than lugging about a switch; it seems like a properly
wired up RJ45 jack should do the trick...

Regards,

Ed Hintz
ed at hintz.org


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