568A vs. 568B

['putertutor]

I decided to look into these two wiring schemes for no other reason than the pure torture of it all. I was deeply rewarded with many tortuous articles that contradicted themselves in manners that betrayed their other worldly origins. I know that on the surface of it, if I lived on an island, I could just pick one or the other, or even make up my own, but in the real world, that seems to not be the case.

Some articles state that I can mix the two on a network, others indicate there may be issues particularly at higher speeds (read: gigabit), others state that they cannot be mixed, ever. I've never (knowingly) mixed these two (I use 568B), but it doesn't sound terrible if they do get mixed. I also understand that A is mostly standard everywhere in the world except for the U.S. (of course) where B is what we like to use.

So, are there any real differences between these two? Which do you use? Can they be mixed on the same network?

 

[trevm999]

What? I don't understand what difference it could make mixing them except for organizational purposes. I don't even think patch cables tell you which why they are wired on their labeling, so most places probably are mixed anyway. I've always used B, but I've heard that A is technically better.

 

[fencepost]

The difference is that the orange and green pairs are swapped. Reading a bit on Cat 6 cables there's mention that some federal contracts require A, and some allegation that performance is better in horizontal runs with it, but I'm not sure what that's based on.

Looking back at the Cat5 Wikipedia article it notes that while the lengths of the twists differ between the colors to reduce crosstalk "the pitch of the various colors is not specified in the standard, pitch can vary according to manufacturer."

Which basically means anything that claims better performance on one type or the other is FUD and depends on the manufacturer and probably lot number of the particular cable with which that "better performance" was measured.

 

['putertutor]

The difference is that the orange and green pairs are swapped. Reading a bit on Cat 6 cables there's mention that some federal contracts require A, and some allegation that performance is better in horizontal runs with it, but I'm not sure what that's based on.

Looking back at the Cat5 Wikipedia article it notes that while the lengths of the twists differ between the colors to reduce crosstalk "the pitch of the various colors is not specified in the standard, pitch can vary according to manufacturer."

Which basically means anything that claims better performance on one type or the other is FUD and depends on the manufacturer and probably lot number of the particular cable with which that "better performance" was measured.

Yeah, the swapped orange and green pairs is about all I could find that was verifiably different. I saw the same thing about horizontal runs too, but I have no idea why that would be or what they are basing it on. This is my frustration here, there doesn't seem to be a clear answer. I know, I know. In the real world, not much difference. I must be on one of my OCD moods right now.

 

[TouchToneTommy]

Before there was Ethernet wiring, AT&T used 8-position jacks for data interfaces and for their Merlin and Definity telephone systems. The wiring pattern that they used for the Merlins would be equivalent to the 568-B, but of course the wiring was Cat-0, and the jacks did not maintain the twists from the termination point to the jack contacts. It was just a matter of putting the correct signals on the correct pairs. Pins 1&2, Pins 4&5, Pins 3&6, and Pins 7&8 constituted pairs.

568-B Ethernet wiring was accepted as an exception to the 568-A wiring, to allow AT&T's wiring to be grandfathered into the specifications.

You could make up your own color code if you wanted, as long as you used it at both ends, and as long as you never SPLIT a pair from the 1&2, 4&5, 36, and 7&8 pairings.

568-A at one end and 568-B at the other will probably work, with auto sensing ports, but of course it is completely wrong. It doesn't pass spec., and without auto sense it doesn't work.

 

[Mercenary Roadie]

As Tommy said 568B is a carry over from AT&T and 568A is compatible with the color code USOC uses for phones for the first two lines, Blue is line 1 and orange is line 2.

 

[YeOldeStonecat]

In the United States, 568B is what is most commonly found. When modifying/changing an existing network in a building, check first to ensure it's 568B....I've come across one or two 568A setups in my lifetime. Makes you scratch your head when you replace a wall jack, do it 568B, test it, see it fail, redo it, fails again..go check patch panel, and find they originally did it 568A.

Performance wise, the difference should not matter. Same cable, same ends, just two pairs are swapped.
If you want to make a crossover cable, you make 1 end A and 1 end B. Of course since the gigabit standard came out, which includes auto MDI-X, crossover cables are no longer needed, the hardware can figure it out (NICs, switch ports).
Technically you can mix runs on the same network....but...for consistency, should make it all the same.

 

[NETWizz]

I was going to basically say what YeOldeStonecat said.

It makes no difference which standard you use; however, most use 568-B in the United States.

Several older Government buildings use 568-A; however, I can assure you ALL new Government wiring in general is 568-B unless specifically contracted to be 568-A.

Either way:
A - A is a straight-through
B - B is a straight-through

A- B or B - A is a crossover

It is important that it be straight through though in the Gigabit specification it is mandatory to have auto MDI/MDI-X, so any new equipment computers/switches really won't care if it is done with one end A and the other B. However, I have ran into older equipment that would not link and being the lazy person I am, I *cough* put a cross-over cable in to cross a cross-over back to a straight-through. ;-)

Do keep in mind historically, Computers and Routers are the same. Computer to computer, computer to router, router to router... you would use a cross-over.

Router to switch, computer to switch (straight thru)