TIA/EIA-568-A, T-568B RJ45 Wiring Standard
For wiring straight-through and cross-over RJ-45 cables
RJ-45 conductor data cable contains 4 pairs of wires each consists of a solid colored wire and a strip of the same color. There are two wiring standards for RJ-45 wiring: T-568A and T-568B. Although there are 4 pairs of wires, 10BaseT/100BaseT Ethernet uses only 2 pairs: Orange and Green. The other two colors (blue and brown) may be used for a second Ethernet line or for phone connections. The two wiring standards are used to create a cross-over cable (T-568A on one end, and T-568B on the other end), or a straight-through cable (T-568B or T-568A on both ends).
To create a straight-through cable, you'll have to use either T-568A or T-568B on both ends of the cable. The diagram depicted on the left and right shows clip of the RJ-45 connector down.
To create a cross-over cable, you'll wire T-568A on one end and T-568B on the other end of the cable.
The straight-through cables are used when connecting Data Terminating Equipment (DTE) to Data Communications Equipment (DCE), such as computers and routers to modems (gateways) or hubs (Ethernet Switches). The cross-over cables are used when connecting DTE to DTE, or DCE to DCE equipment; such as computer to computer, computer to router; or gateway to hub connections. The DTE equipment terminates the signal, while DCE equipment do not.
More on straight-through and cross-over connections
The RJ45 data cables we use to connect computers to a Ethernet switch is straight-through cables. As noted above, the RJ45 cable uses only 2-pairs of wires: Orange (pins 1 & 2) and Green (pins 3 & 6). Pins 4, 5 (Blue) and 7, 8 (Brown) are NOT used. Straight-through cable, as its name suggests, connects pin 1 to pin 1, pin 2 to pin 2, pin 3 to pin 3, and pin 6 to pin 6. Cross-over cables are used to connect TX+ to RX+, and TX- to RX-, which connects pin 1 to pin 3, pin 2 to pin 6, pin 3 to pin 1 and pin 6 to pin 2. The unused pins are generally connected straight-through in both straight-through and cross-over cables.
To network two computers without a hub, a cross-over cable is used. Cross-over cable is also used to connect a router to a computer, or ethernet switch (hub) to another ethernet switch without an uplink. Most ethernet switches today provide an uplink port, which prevents a use of cross-over cable to daisy chain another ethernet switch. Straight-through cables are used to connect a computer to an ethernet switch, or a router to an ethernet switch.
Pin Number Designations
There are pin number designations for each color in T-568B and T-568A.
Pin Color Pin Name Color Pin Name
--- ------------- -------- ------------- --------
1 Orange Stripe Tx+ Green Stripe Rx+
2 Orange Tx- Green Rx-
3 Green Stripe Rx+ Orange Stripe Tx+
4 Blue Not Used Blue Not Used
5 Blue Stripe Not Used Blue Stripe Not Used
6 Green Rx- Orange Tx-
7 Brown Stripe Not Used Brown Stripe Not Used
8 Brown Not Used Brown Not Used