T568A vs T568B: RJ45 color code
Only pins 1, 2, 3 and 6 differ: the green and orange pairs trade places.
T568A
T568B
| Pin | T568A | T568B |
|---|---|---|
| 1 | White/green | White/orange |
| 2 | Green | Orange |
| 3 | White/orange | White/green |
| 4 | Blue | Blue |
| 5 | White/blue | White/blue |
| 6 | Orange | Green |
| 7 | White/brown | White/brown |
| 8 | Brown | Brown |
Pairs: 1 blue, 2 orange, 3 green, 4 brown.
Which one to use
Match the existing site, or whatever the job spec says. Both work the same electrically.
T568B is common in US commercial work. With no spec and no existing cabling, pick one and use it everywhere.
Straight-through vs crossover
Straight-through: same standard on both ends. Use it for patch cords and permanent links.
Crossover: T568A on one end, T568B on the other. Current switches handle this on their own (auto-MDIX), so you rarely need one.
Straight-through
Crossover
10/100 vs gigabit pins
10BASE-T and 100BASE-TX use pins 1, 2, 3 and 6. Gigabit and faster use all eight, so terminate all four pairs on every run.