A crossover cable is a type of UTP cable. UTP cables have eight wires, which are twisted together to make four pairs of wires. At the end of the cable is an 8P8C connector, commonly known as an RJ45 connector.
Wires that are inside the UTP cable must connect to specific pins inside the connector. Pin 1 at one end of a straight-through UTP cable will connect to pin 1 at the other end. This also applies to pins 2, 3, and the rest.
Crossover cables are different. Four of the wires don’t line up at both ends. Pins 1 and 3 are crossed over. So are pins 2 and 6.
In times past, crossover cables were used when connecting one switch to another switch. They were also used when connecting one workstation to another workstation.
Basically, some pins are used for transmitting signals, while others are used to receive them. The wires are crossed over to make sure that these pins line up correctly.
These days, crossover cables are rare. This is because of a modern feature called Auto-MDIX. A device with this feature can detect the cable type in use and change the pins that send and receive data as necessary.
This just means that we don’t need crossover cables anymore. We can use the more common straight-through cable for everything.