Re: OT Any web site that teaches how to make LAN cable connection
On Wed, 27 Mar 2002, Elizabeth Barham wrote:
> > is there Any web site that teaches how to make LAN
> > cable connection i mean like cross over & straight
> > wires ? also you can ask question lelated to cabeling
> > ?
Use www.google.com, you will find good answers for your questions quite
easily. E.g.: I found http://www.alatec.com/info/rj45.html in less than 2s.
> There's straight-thru and crossover - for crossover, they should be
> reversed. If the original is BLUE-RED-GOLD then the matching one
> should be GOLD-RED-BLUE (example is for explanatory purposes only).
> Straight-thru is literally that ; the wire on both ends should look the
> *exact* same through the RJ-45.
>
> Straight-Thru:
> 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
> (bottom) (bottom)
>
> Cross Over:
> 1 2 3 4 5 6 7 8 8 7 6 5 4 3 2 1
> (bottom) (bottom)
That is quite wrong!
*Ethernet* LAN cables are polarized twisted pairs, with four pairs in one
cable. Usually only 2 pairs are used for 10 and 100 Mbit/s ethernet. You
*MUST* keep each signal in a twisted pair (i.e. TX+ and TX-, RX+ and RX-),
which a 12345678 12345678 wiring will NOT do.
If you're not an EE and don't know anything about waveguides, at the very
least do the wirings as the standards tell you to, instead of doing it in
a way that looks pretty or something equally unwise.
Green and white-green are a pair; if you connect TX- to one, you must
connect TX+ to the other. And you must connect TX+ to RX+ and TX- to RX-,
so don't go wiring 12 in one tip, and 21 in the other. Hubs/switches and
NICs have the TX and RX positions reversed, so a straight cable will do the
right thing.
For 10BaseT and 100BaseTX networks, the correct wiring is:
12356478 12356478 (straight, aka NIC<->HUB), where 12 is the first
pair, 34 the second pair, etc. DO NOTICE THE SPLIT IN THE SECOND PAIR!
Crossover is: 12356478 34156278 (NIC<->NIC)
Only the first+second and third+sixth positions are used in 10BaseT and
100BaseTX. You wire it 12345678 12345678 and you will be inducing a lot of
noise in both the ethernet wiring, and anything else next to it. If you
have been doing such a stupid thing around your home or office, redo it
right.
And please respect the minimum and maximum lengths for the cabling, or you
will have problems.
--
"One disk to rule them all, One disk to find them. One disk to bring
them all and in the darkness grind them. In the Land of Redmond
where the shadows lie." -- The Silicon Valley Tarot
Henrique Holschuh
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