T568A / T568B
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Stands for: T568A and T568B termination pinouts (ANSI/TIA-568)
The two TIA-568 pinouts for terminating twisted pair on RJ45 - identical performance, different wire-to-pin order.
T568A and T568B differ only in swapping the green and orange pairs' positions. Either works; what matters is consistency - both ends the same scheme yields a straight-through cable, one end of each yields a crossover. B is the de facto habit in much of the market, A is preferred in some government and residential specs. The rule every installer learns: pick one scheme per site and never mix.
T568A and T568B are the two standard pin assignments for eight-position modular plugs, differing only in whether the orange and green pairs are swapped. Electrically they are equivalent, and a link works as long as both ends use the same one.
The rule that follows is simple and constantly broken: pick one and use it throughout a site. Mixing them produces a crossover cable, which modern equipment with automatic MDI-X detection will silently accommodate, which is worse than failing because the inconsistency survives undetected until someone connects equipment that does not. Labelling the standard in the wiring closet is the whole of the discipline.
Also known as: t568a, t568b, pinout, wiring scheme