EIA/TIA 568A & 568B Standard

The cable color code is the 568B standard on each end of a straight-through 10/100BaseT cable. If a crossover cable is needed, use the 568A standard on one end and 568B on the other end.
EIA/TIA 568-568B
Crossover Cable
1 Rx+ 3 Tx+
2 Rc- 6 Tx-
3 Tx+ 1 Rc+
6 Tx- 2 Rc-
Straight Through Cable
1 Tx+ 1 Rc+
2 Tx- 2 Rc-
3 Rc+ 3 Tx+
6 Rc- 6 Tx-

Use a straight thru cable assembly,568B on both ends when connecting Hub to Xcvr or NIC Card. When connecting hub to hub, Xcvr to Xcvr, or NIC to NIC, the wires must crossover at the opposite end of the cable assembly,use the 568B on one end, 568A on the other end.

Interconnecting Your Hubs, Transceivers, and NIC Cards

A crossover cable is required when connecting a Hub to a Hub, or a Transceiver to Transceiver, or NIC to NIC card, or Transceiver to NIC card. When connecting a Hub to a transceiver or NIC card, a straight through cable is always used. Please Note: Some products are equipped with internal switches that can internally cross the twisted pairs.

10BASE-T Crossover Wiring

When connecting two twisted-pair MAUs together over a segment, the transmit data pins of one eight-pin connector must be wired to the receive data pins of the other, and vice versa. The crossover wiring may be accomplished in two ways: with a special cable or inside the hub.

For a single segment connecting only two computers you can provide the signal crossover by building a crossover cable, with the transmit pins on the eight-pin plug at one end of the cable wired to the receive data pins on the eight-pin plug at the other end of the crossover cable and vice versa.
Crossover Wiring

FIGURE 5.2 10BASE-T crossover cable

However, when you are wiring multiple segments in a building it's much easier to wire the cable connectors "straight through," and not worry about whether the wires in the jumper cables or other twisted-pair cables in your building have been correctly crossed over. The way to accomplish this is to do all the crossover wiring at one point in the system: inside the multiport hub.

The standard recommends that the signal crossover be done internally in each hub port. If the crossover function is done inside a hub port, then the standard notes that the port should be marked with an "X."