Am Tue, 4 Apr 2017 15:05:13 -0600
schrieb the...@sys-concept.com:
> On 04/04/2017 02:56 PM, Kai Krakow wrote:
> > Am Tue, 4 Apr 2017 14:28:23 -0600
> > schrieb the...@sys-concept.com:
> >
> [snip]
> >>
> >> I have reconnected another cable and the unit in remote location
> >> works. Both cable have a good pinout but one is working and the
> >> other is not. Both cable are sunning inside wall (I presume same
> >> path). Without special tools/testing equipment it is hard to trace
> >> these problems.
> >
> > You could try the problematic cable with only 100 MBit. If this
> > works, I'm pretty sure that some of the wires are broken or have
> > incorrect order. Keep in mind, tho, that the inverse assumption of
> > such tests is not true.
>
> Yes, the testing took was cheap it came with the stripper.
> Though, if the cable order was wrong, wouldn't the light on the tester
> jump in different order? The light on the tester lights up
> sequentially, so I assume the order is correct. Besides that "bad"
> cable was working OK for a day.
No, if you have the same wrong on both sides, the LEDs will still show
correct blinking order. Think of it like this: If you use order
7-5-3-1-2-4-6-8 on both sides, blinking LED 1 on one side will blink
the same LED on the other side because they both connect to wire 7. But
the twisted pairs that should be twisted are no longer because now you
connected pair 1 in the connector to wire 7 and 5 which belong to
different pairs in the wire. The wire twists pair (7,8) and (4,5). On
the long run, interference now cannot be canceled out because this
only works if wires are twisted in the same pair. The connector (and
ethernet standard) expects the following pairs on the connector:
A-A-B-C-C-B-D-D
1-2-3-4-5-6-7-8
For electrical reasons it also expects a white wire alternating with a
colored pair, which makes the following pairs:
A = (1,2)
B = (3,6)
C = (5,4)
D = (7,8)
Or:
A-a B c-C b D-d
^_____^
With the capital letters being either all white or all colored (this
doesn't depend as long as it's the same on both sides).
You could open the problematic wall outlets and check the cabling
yourself. Keep in mind that unmounting the wall outlet may make the
problem of bent cables even worse due to moving and bending the wires
even more. Usually, the company that installed the cabling should've
done a frequency spectrum test on each wire pair. If you didn't get it
you should ask for it. In my company, we deny any network problems of
our delivered equipment unless such a test has been done and presented
to us. Such a test may cost a few extra bucks but should be part of
such an installation (done by the electrician before handling the
project over to its customer).
Depending on the inside of the RJ45 wall outlet, you can fix it
yourself. For the cheaper LSA based internal connectors you need an LSA
tool (it's inexpensive). Don't try to use a screw driver to mount the
wires. The more expensive modular connectors are easy to mount: Just
insert the wire pairs properly into the holes, properly and cleanly cut
the wires off the other end, and push the connector module in place
(take care of proper alignment). The modular connectors also
properly connect shielding, so properly connect that. Usually those
connectors come with a small manual how to do it. Order new ones, don't
reuse. Cut off 1-2 inches from the old connector cabling.
At least in Germany I know those two kinds of connector outlets.
> And yes, the room the cable is passing by has all kind or x-ray
> machine.
There's definitely problems with x-ray machines. Usually, those are
connected by fiber optics (at least dental x-ray machines). You want to
find a separate cabling way for your network, and also ensure that the
power circuits are different between those machines and your network
equipment.
Ensure that shielding is properly passed along the complete cabling,
including the patch cable from the wall outlet to your machine. Proper
shielding is essential in such environments.
We had one issue at a company running cooling generators and having
unstable network. It was eventually resolved somehow but we think that
the generators induced some non-harmonic distortion into the cabling of
the complete building. I think it was resolved when they rechecked
proper shielding on all cabling and machines.
> I'll try to test it 100Mbit (limit the speed); just need to find out
> how.
Maybe this can be done with ethtool.
--
Regards,
Kai
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