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Re: OT: Strange network cable problem
On Thu, Sep 20, 2001, Alon Altman wrote about "Re: OT: Strange network cable problem":
> On Thu, 20 Sep 2001, guy keren wrote:
>
> > > The cable is wired correctly (I have another one with exactly the same
> > > wiring that works).
>
> I did. All connection OK. No shorts.
If indeed the wiring is correct, and wiring the ends again doesn't help
(just in case you made a mistake you're missing), and you're sure this isn't
a software problem (to make sure of that, make sure that another wire works
for you), then you're probably left with only one explanation:
The wire itself is faulty.
You know that wires for 100Mb/s ethernet are called "Category 5" UTP
(unshielded twisted pair), right? This category 5 (and I'm sure some of the
EE'ers on this list can explain it much better than I can) has to do with
the impedance (resistance) of the wire, with the level of cross-talk between
the seperate wires, uniform twisting of the wires, and so on. A UTP cable
can look ok, and even check out ok in a DMM (Digital MultiMeter), but because
of faults in it not comply with the stricts category 5 requirements, and
when you try to pass the ethernet signal through it the noise on the faulty
cable will overwhelm the signal. Because the recieve and transmit pairs are
seperate, it is possible to have only one side of the communication go bad.
You can try setting the network cards on both sides to 10Mb, and see if
the communication now works: 10Mb is more tolorant to relatively-small noise
on the line. You can also try "playing" with the wire, perhaps moving the
entire thing to a different area of the house with different levels of
electromagnetic interference, and see if it suddenly works. But best of all,
you can just dump this wire and get another one. If you got this wire at
a store, you should ask to replace it. Good stores might even have a category
5 compliance tester, though this is not something a person would normally have
in his house.
> > btw, how long is the other cable that works for you? does it work between
> > the same computers and same network cards?
>
> It's about 1-2m and it works between same comps and NICs. I've tried the
> long cable between different NICs (all CNET) with same results.
I am using a category 5 wire (with the thin, soft, insulation so it will be
easy to roll when the connection is not needed) around 12 meters long, with no
problems. 2m is definately not too long.
--
Nadav Har'El | Friday, Sep 21 2001, 4 Tishri 5762
nyh@math.technion.ac.il |-----------------------------------------
Phone: +972-53-245868, ICQ 13349191 |Enjoy the new millennium; it might be
http://nadav.harel.org.il |your last.
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