Re: Networking problems.

[Keith Doxey <ukha@xxxxxxxxxxx>]

Quoting Stuart Grimshaw <stuart@xxxxxxx>:

> Out of the 12 points he has tested so far (by plugging a PC in and
trying to
> connect to a device in node 0), 1 works, 1 has tremendous packet loss
& the
> rest all fail.
>
> All these points test OK with a basic flashing light network tester,
ie all
> cables are pin2pin and none appear to be broken.
>
> The origional wireing was faulty, with wires crossed and all sorts,
his
> sparky has rewired the faulty sockets, at the socket end I beleive.
>

Sounds distinctly like "Split Pairs" to me. As you say,
electrically there is
full conductivity using a DC cable tester. If the pairs are split* then the
cable effectively becomes a long transformer winding and couples what
should be
separate circuits together.

I have had experience of this on telephone lines where the pairs were split
and
the crosstalk between the two lines was so great it was as if both phones
were
on the same line but electrically the line tested perfect.

* Split pairs definition.


CORRECT

1 ---- WHITE/Orange ---- 1 Pair 2
2 ---- ORANGE/White ---- 2 Pair 2
3 ---- WHITE/Green ----- 3 Pair 3
4 ---- BLUE/White ------ 4 Pair 1
5 ---- WHITE/Blue ------ 5 Pair 1
6 ---- GREEN/White ----- 6 Pair 3
7 ---- WHITE/Brown ----- 7 Pair 4
8 ---- BROWN/White ----- 8 Pair 4

INCORRECT (Exagerated Example!!!)

1 ---- WHITE/Brown ----- 1 Pair 2
2 ---- ORANGE/White ---- 2 Pair 2
3 ---- WHITE/Blue ------ 3 Pair 3
4 ---- BLUE/White ------ 4 Pair 1
5 ---- WHITE/Orange ---- 5 Pair 1
6 ---- GREEN/White ----- 6 Pair 3
7 ---- WHITE/Green ----- 7 Pair 4
8 ---- BROWN/White ----- 8 Pair 4

In the incorrect example the pins are all connected correctly BUT the pair
allocation is all wrong

eg
Pair 1 = White/Orange + Blue/White
Pair 2 = White/Brown + Orange/White
Pair 3 = White/Blue + Green/White
Pair 4 = White/Green + Brown White

The actual colours dont really matter ( as is evident by T568A and T568B
using
different colour codes but the same PHYSICAL connections and pairing) but
it is
preferable to stick to a recognised standard but the pairing of the cable
does.
It definately wont work at high frequencies.

What CAT5 sockets has he used?
Some have a strange pinout whereas most allow the cable to be terminated in
colour code order W/BL/W/O/W/G/W/BN.

Hope that helps.

Keith

www.diyha.co.uk
www.kat5.tv


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