[ILUG] [OT] Networking...

[Christian van den Bosch]

Niall O Broin wrote:

 > Consider yourself corrected :-) Two pairs are used for 100BaseT &
 > 10BaseT.

Correct. The orange pair (pins 1 and 2) is TX, the green pair (3 and 6) 
is RX.

 > So it is possible to run two connections over one run of Cat-5 cable,
 > and as somebody else pointed out, you can even buy little gadgets to
 > do that and save you rewiring sockets at each end.

The ready-made ones are astonishingly expensive; on a budget it may be
better to get a cheap&nasty gender-bending RJ45 inline coupler (if you
want to split an existing cable, as opposed to plugging two cables into
one socket) and making up a couple of RJ45 Y cables to plug onto each 
end of your existing cable. Pins 1, 2, 3 and 6 are the ones you want to
connect to the NICs at each end.

 > I would suspect that maybe over longer cable runs this mightn't be as
 > reliable as a very reliable thing because of crosstalk, but that's
 > really only guessswork/gut feeling.

Correct. You'll also have more radiated emission (still not much because
each twisted pair carries a differential signal) because in the 'proper'
configuration the blue and brown pairs are there to absorb this (and on
any decent NIC/hub/switch etc are appropriately terminated).

Then, of course, there's PoE (power over ethernet) which uses the blue
and brown pairs to carry power, typically at 48V, for such devices as
routers, embedded computers, wireless APs etc.

More on the above at http://ocean.ucc.ie/~cjvdb1/html/cwt.shtml if
anyone wants it.

cjb

http://ocean.ucc.ie/~cjvdb1/