Re: Ethernet Cable Question

[Ramon Gandia <rfg nook net>]

Aaron Prohaska wrote:
> 
> I'm trying to connect my laptop to my desktop (both linux) and have been
> told I can do this without a hub using crossover cable. So I am
> wondering what the difference is between regular ethernet cable and
> crossover cable?

There are four wires involved in a 10BaseT ethernet.  Two wires
(one pair) is used to send signal in one direction, and the other
two wairs (another pair) is used to send the signal in the other
direction.

Computers and hubs have the little pins on the jacks just
backwards from each other.  If you have a regular straight
cable, then the computer's transmit pins connect to the hub's
receive pins and vice versa.  Thus a computer can communicate
with a hub.

If you connect two computers with a straight cable, then the
transmit pins are looking at each other, and the two receive
pair of pins are connected to each other.  Thus, it is not
possible to communicate.

You get around this by one of two ways.  ONe method uses a
so-called crossover cable.  This type of cable has the ends
wired differently so that the transmit signal from the computer
ends up at the receive pins of the other computer and vice
versa.

The other method is to use two regular straight cables, but
use a crossover block in the middle.  You have to be a bit
careful here because crossover blocks intended for telephone
use -even if they have rj-45 jacks- are not suitable.  Ethernet
crossovers are hard to find, but you can get two RJ-45 wall 
jacks and wire them to each other with hookup wire to do what
you want.

Crossover cables are easily obtainable, although the variety
is less varied.  DALCO electronics has them, as does Cables USA,
and a bunch of other mail order outfits.  They cost about the
same as regular cables.

Hubs are now going as low as $29.95 for a 4-port hub.  You should
look into this solution as the little hub is much more versatile
and you avoid having different types of cables.  I had a time
here when no matter what I did the thing would not work....and
it turned out I had mixed up my cables.  Then, thinking it was
a bad cable, I chopped the ends off and threw it in the trash.
There went my nice crossover cable! 


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Ramon Gandia ================= Sysadmin ================ Nook Net
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