Re: swith (cross) ethernet cable

Rod Hauser (rhauser@mail.wavetech.com)
Wed, 1 Sep 1999 14:21:40 -0500


whatis.com only has the definition, but links:
http://orcon.co.nz/~seeby/crossover.html
and
http://isis.livingston.com/tech/technotes/100/160002.html

I lost my 1-page doc that I'd done on the topic... which has what these are
lacking: a diagram of the "end" of an RJ-45, with pins 1-8 numbered so you
don't get them mixed up. The confusing/enlightening point of RJ-45 is that
the pins are paired, but not in order: (terrible diagram coming... anyone
got a better ASCII or weblink/graphic one?)
12345678
-------
| |
-------
-- <- this is the "tab" on the RJ-45, with the connecting end
facing you, the cable/back away from you.

Now to understand electricians... never mind. These are pairs. The pairs
of wires are (starting in the middle)
pair1: 4-5
pair2: 3-6
pair3: 1-2
pair4: 7-8

To deconstruct and reconstruct the reason that a crossover cable is a
crossover, what you're actually crossing are TX and RX (one wire in each
pair) so that a straight-through cable takes pair2 (pins 3&6) to the same
pair2 on the other (or both) ends, and similarly for pair3 (pins 1-2). A
crossover cable takes pair2 -> pair3 and pair3->pair2. That's confusing.
Just look at the diagram on the link.

The only point I have to add to that is: they are in pairs. And
electricians are at least as anal-retentive as computer programmers -- I
didn't mention wire color standards !

Rod Hauser Curriculum Manager - Linux
rhauser@wavetech.com Wave Technologies
314-692-1916 St Louis MO, 63141

> Hello. I have a silly question -- where do I find a layout (scheme) of a
> cross(ed) ethernet cable, the one they use for switches?
>
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