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10/100BaseT Ethernet wiring is based upon 8-pin modular jacks. Two wiring guidelines are offered in Electronic Industry Association (EIA)/Telecommunications Industry Association (TIA) standards:

EIA/TIA 568A
EIA/TIA 568B

A standard Ethernet NIC card (DTE) has the following RJ-45 modular pinout:

Pin Function

1 Tx+

2 Tx-

3 Rc+

6 Rc-

The RJ-45 modular jack has 8 conductors/pins. Viewed from the front:

TIA-568B

TIA-568B is the most common wiring scheme used in 10/100BaseT configurations. The standard Ethernet "Patch" cable that connects a hub port to a NIC card uses TIA-568 wiring at both ends of a "straight-through" cable:

TIA-568A

In TIA-568A wiring schemes, the White/Orange and White/Green pairs are transposed. An Ethernet "Crossover" cable can be made by using TIA-568B at one end of the cable and wiring to TIA-568A at the other end of the cable. These "Crossover" cables can be used to interconnect NIC cards directly, without the need for a hub. "Crossover" cables are usually "RED" in color: