[rescue] Rescued Sun servers, now what?!

Lex Landa brooknet at imap.cc
Mon Feb 20 13:26:17 CST 2012


I knew that you folks would give me a good explanation - and make it
interesting, too (who'd have thought that a simple cable could have such
a rich history?)

On Mon, 2012-02-20 at 10:44 -0500, Mouse wrote:

> Hold one of the ends so the shiny metal contact surfaces face you (the
> locking tab will be behind the rest of the connector).  Now look just
> adjacent to those contacts, in the direction towards the cable.  You
> should see a wire colour for each contact (half of them will probably
> be white).

I can't do that for the cable that I have because I then would not be
able to send this mail - that cable is plugged into my router!  Still, I
have a few more lying around and I can see that it's exactly as you
describe: brown, white, green, white, blue, white, orange, white.

> Now compare that with the other end.  If the colour pattern is the
> same, it's a straight-through cable; if two of them have been switched,
> it's a crossover cable.

The same - it's a straight-through.

>   (That's assuming it's a twisted-pair-Ethernet
> cable at all, of course; while it's overwhelmingly likely it is,
> especially in view of the markings you quote, there are a few other
> things RJ45-style 8P8C connectors are used for.)

PBX?  ISDN?  The connectors are different for the latter, I think - I
used to have an ISDN connection: I'll start a new thread for that, as I
have a Fritz! PCI card somewhere that I should get rid of.
Unfortunately, I have to dig it out of a huge pile of cruft created by
the builders, when they installed the central heating.

> If you have an ohmmeter, you can verify that way (you may need small
> bits of wire to make contact with the connector surfaces).  A
> straight-through cable connects pin 1 on one end to pin 1 on the other
> end, 2 to 2, etc, all the way up to 8 to 8; a crossover cable connects
> 1 to 3, 2 to 6, 3 to 1, 4 to 4, 5 to 5, 6 to 2, 7 to 7, and 8 to 8.
> (The peculiar-looking choice of wires to swap is of historical origin...

I'm thinking that the phrase 'twisted pair' explains it: the pairs are
swapped, but the common wires are not.  I made up a custom cable a few
years ago, with a length of Cat-5 cable and two wall sockets.  I had to
test the connections (my ineptitude with electronics extends to not
being able to wire-up IDC cables) and there were open circuits on a few
of the wires.  It was a 50-metre (164-foot) bit of cable and was to link
two houses (my cousin's place, and mine) but he moved out before I had a
chance to use it.  We had a 57.6K PPP link going for a long time, in the
90s - then, Wi-Fi came along.  Getting the early wireless cards
configured made me wish that I'd stuck with the cable idea - all those
MIBs and config files..

>  (The wire is marked as
> gigabit-ready, yes, but that does not necessarily mean the cable was
> prepared for gigabit use, though it probably is.)

It is; it's a recently-purchased cable ('recent' as in two years ago).



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