A typical ethernet cable has eight wires. You also have shielded cables which contain a grounding pin. For an ethernet connection to work, you only need to use four of these wires – two transmit wires, and two receiver wires. This leaves two pairs of wires redundant in most cables that can serve a different purpose.
One of these purposes is to use them to transmit power. This is known as Power over Ethernet (POE), but they can also be used as a second data connection. The easiest way to implement this, is to purchase a pair of ethernet splitters. They simply plug into either end of a network cable and convert the pin connections. Obviously, you can do this manually, but by using a specifically designed device you will get a more professional setup.
- Please note that gigabit ethernet connections require use of all four twisted pairs (8 wires).