A crossover cable uses different wiring standards on each end to facilitate direct communication between two devices of the same type (e.g., computer to computer, switch to switch). The two standards involved are T568A and T568B. Here's a breakdown of the color coding:
Understanding T568A and T568B
The two common standards for wiring Ethernet cables are T568A and T568B. A straight-through cable uses the same standard on both ends. A crossover cable uses T568A on one end and T568B on the other.
Crossover Cable Color Codes
The following table shows the color code for a crossover cable, with one end wired to T568A and the other to T568B. When looking at an RJ45 connector with the clip facing away from you, and with the brown pair on the right, Pin 1 is on the left. Odd-numbered pins are striped and even-numbered pins are solid.
| 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 |
How to Identify a Crossover Cable
The easiest way to determine if a cable is a crossover cable is to look at the color coding of the wires in the RJ45 connector. If the color order is different on each end, it's a crossover cable. Specifically, look at the positions of the orange and green pairs. If they are swapped between the two ends, it's a crossover cable.
When to Use a Crossover Cable
Crossover cables were traditionally used to connect two devices of the same type directly, such as two computers or two hubs. However, most modern network devices support Auto-MDIX, which automatically detects the cable type and adjusts accordingly, making crossover cables less necessary.
In summary, a crossover cable utilizes T568A on one end and T568B on the other, effectively swapping the transmit and receive pairs to allow direct communication between similar devices.
