I've had many conversations about the proper way to make your own
ethernet cables. There are two standards, 568A or 568B. I was always
under the impression that you cannot make up your own wiring pin
layout because it would cause crosstalk, or interference. I know that
when you pick a standard, you should stick with that standard and you
should not use another. My question is, can you use any random pinout
when wiring your ethernet cables provided that you use it consistently
throughout the network?

If you are using a modern piece of equipment it does not matter,
because the network interface card will automatically sense which
method you chose and do an "internal crossover" if necessary.  So, you
can do both A, both B, or A to B or B to A, it doesn't matter -- as
long as both pieces of equipment being connected aren't as old as you
are. ;)

Whoops, I read that wrong.....why would you want to use a random layout?

Yes, use one of the standard layouts. Each of the pairs of wire has a
different number of turns. They are made for certain configurations.
Either configuration works as well according to a Pentascanner.

If you end up mismatching wires where you get mixed colors in a pair
you will greatly reduce the speed that can be used on the cable.

"why would you want to use a random layout"
Well, that's what I'm getting at. I know people that are convinced you
can use any pin layout you want as long as they are the same on both
sides of the cable. I don't think this is right because there are only
two pairs used. Each of those pairs are twisted around themselves. If
you use a randmon pin layout, you lose the ability of the wire to
cancel out it's own crosstalk....at least that's what I believe. I
just need proof.

dvati0n-ga  - 

I can tell you from working with local area networks for the past 10
years, that in all reality, it doesn't matter which one you choose, as
long as you pick ONE and stick with it throughout your network.

BUT : if you want to use the industry standard - which is recommended
if you ever want to use any premanufacturered cables, it is suggested
to use the more common 568B.

I recently wired my entire house for CAT5e, before a fiber-optic
installation.  The first port I wired was 568A, but after doing
research, I went back and made it 568B, and continued with 568B
throughout the entire network.

Stating that, here is my research on this topic

This site explains the difference between the two wiring schemes :
http://telecom.tbi.net/enetpins.html

More details for residential LAN cabling :
http://ceenews.com/mag/electric_residential_lans_hard/

A brief history of data cabling standards :
http://www.jimhayes.com/uncleted/structed.html

This site specifically talks about crosstalk - but only mentions that
you need to keep the wiring twisted to prevent it, not which standard
to use :
http://www.aptcommunications.com/ncode.htm

This site actually has a great definition of crosstalk, as well as a
Tutorial as to how to wire, but doesn't come right out and say WHICH
standard to use :

http://www.lanshack.com/cat5e-tutorial.asp

The above site goes on to say that there is NO DIFFERENCE in wiring schemes : 

"It is very important to note that there is no difference, whatsoever,
between the two wiring schemes, in connectivity or performance when
connected form one modular  device to another (jack to Patch panel,
RJ-45 to RJ-45, etc.), so long as they (the two  devices) are wired
for the same scheme (A or B). The only time when one scheme has an
advantage over the other, is when one end of a segment is connected to
a modular  device, and the other end to a punch block. In which case,
the 568A has the advantage of having a more natural progression of
pairs at the punch block side. More on 568 A&B later on. "


Let me know if that works for you?
Brady

Google search method : 
ethernet wiring scheme 568 history

Google search method : 
ethernet wiring scheme 568 crosstalk

brady173-ga,

Great information...thank you. 
Just to clarify...I realize that 568A and 568B both work well. This is
what I'm getting at:
568A goes like this:
PIN - COLOR
1   - W/G  ----|
2   - G    ----|
3   - W/O  --------|
4   - B    ----|   |
5   - W/B  ----|   |
6   - O    --------|
7   - W/Br ----|
B   - Br   ----|

And a similar pin layout for 568B. Both of these standards work for
data. I get that.

Where I need clarification is whether or not I could use something like this...

1   - W/G  ----|
2   - G    ----|
3   - B    ------|   
4   - W/B  ------|   
5   - O    ----|
6   - W/O  ----|
7   - W/Br ------|
8   - Br   ------|

Or this....


1   - W/G  --------|
2   - W/B  ----|   |
3   - B    ----|   |
4   - G    --------|   
5   - O    -----------|
6   - Br   ----|      |
7   - W/Br ----|      |
8   - W/O  -----------|

And most importantly...WHY couldn't I use the above two examples? Is
this documented anywhere?

Hi, dvati0n. I believe I can answer your question. In one of your last
few comments, you wrote:

"I know people that are convinced you
can use any pin layout you want as long as they are the same on both
sides of the cable. I don't think this is right because there are only
two pairs used. Each of those pairs are twisted around themselves. If
you use a randmon pin layout, you lose the ability of the wire to
cancel out it's own crosstalk....at least that's what I believe. I
just need proof."

You are correct in your belief. Although you COULD theoretically use a
random pin layout, it would not be very resistant to interference and
crosstalk. You are also correct that the twisting of the pairs is what
ensures this resistance.

10BaseT and 100BaseT use two pairs, corresponding to pins 1/2 and 3/6.
Here's how the pin assignments are broken down:

Pin 1: Transmit +
Pin 2: Transmit -
Pin 3: Receive +
Pin 6: Receive -

Because pins 1/2 are used for transmit, and pins 3/6 are used for
receive you need to ensure one pair is used for each. If you split
pairs--for example connecting orange to pins 1 and 3--you'll lose the
ability for the pair to cancel out interference because of the
twisting.

The other pins, when used for 10/100BaseT, don't matter, and could
have a random layout. In fact, you can make a cable using only two
pairs, as long as they're connected to pins 1/2 and 3/6.

Notice that with both T568A and T568B, pins 1/2 and 3/6 both are
configured to use one pair each. For T568A, it's green for 1/2 and
orange for 3/6. For T568N, it's orange for 1/2 and green for 3/6. So
you may effectively use either wiring standard, as long as you use the
same standard on both ends of the cable!

BIG NOTE: Everything I wrote above is applicable to 10BaseT and
100BaseT, but NOT 1000BaseT (aka gigabit). For 1000BaseT, all four
pairs are used: 1/2, 3/6, 4/5, and 7/8. Notice that if you follow
either the T568A or T568B wiring standard, you'll be covered for this
as well, since the only difference between the two are swapping of the
orange and green pairs.

I went digging for some good reference information on this for you to
read, and here's a nice page that documents the different wiring
standards:
http://www.ertyu.org/~steven_nikkel/ethernetcables.html

Here's a good article on twisted-pair cable:
http://www.answers.com/topic/twisted-pair

I hope this helps!

Beet Root