I read your reply regarding mixing 568A and 568B with interest. With all due respect, I am really skeptical that there's enough of a difference in the impedance between the green pair and the orange pair to have any real difference with data transmissions.
Have you ever actually measured this with your own eyes? I have certified tons of cat5e over the years and it's never been an issue.
One of the testers I have used came with test leads hardwired into a proprietery plug that screwed into the tester. They only gave you one pair of leads; if different leads were necessary for 568A and 568B pinout, they'd have needed to give you two.
Thinking about it more, having bought thousands of patch cords over the years, never had anyone even offered whether to sell me 568A or 568B - if it was a big deal, you'd think people would look for it. LAN admin types are notoriously fussy about details that are of no practical importance.
Regarding impedance, I would think that the length of the conductor is the main determinant. Different twist ratios are going to make the actual length of the conductors a little different in each pair. This skew is at times a problem on long runs with lousy cable. But by mixing a 568a link with 568b patch cords, you'd actually get less of a total difference in lenth between pairs, and more even impedance / delay skew pair to pair. Not that I think that's of any practical importance. (I am admittedly out on a limb with this, please by all means straighten me out if I am off base.)
Anyways - thanks to pain in the axe VOIP systems I have done a LOT of low level network monitoring and etc. this past couple years. I have seen MANY problems caused by marginal patch cords, but not one by mismatched 568a/568b patch cords. So even if there is a measurable difference, I can say that in my experiece, it seems to be within the tolerances of the encoding etc., too small to cause bad packets.
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