These are three of the most common Ethernet standards used today:
10BASE-T (Ethernet), 100BASE-TX (Fast Ethernet, or FE), and 1000BASE-T (Gigabit Ethernet, or GE) that use UTP cabling.
Telecommuncations Industry Association (TIA) and Electronics Industry Alliance (EIA) define the standards for UTP cabling, color coding for wires and standard pinouts on the cable.
The UTP cable requires two pairs of wire for 10BASE-T and 100BASE-TX and four pairs of wire for 1000BASE-T.
Two EIA/TIA pinout standards are T568A and T568B.
T568A Pinout Standard:
Pair 1 Blue White/Blue
Pair 2 Orange White/Orange
Pair 3 Green White/Green
Pair 4 Brown White/Brown
T568B Pinout Standard:
If a cable has T568A color wiring on both ends, then it’s a straight through cable.
If a cable has T568B color wiring on both ends, then it’s also a straight through cable.
If a cable has T568A color wiring on one end and T568B color coded wiring on the other end, then it’s a crossover cable.
The only difference between T568A and T568B is that pair 2 and 3 are swaped.
For the 1000BASE-T, straight through cables connect wire at pin 1 to pin 1 , pin 2 – pin 2 and so on.
For the 1000BASE-T, crossover cable crosses wire pairs between pins (1,2 and 3,6) and (4,5 and 7,8).
Nowadays, all modern devices use Auto-MDIX, which is a feature that notices wrong cabling pinouts, and configures the connection appropriately, making the cable to work and removing the need for crossover cable.