What is it?
Power over Ethernet (PoE) is a technology for providing devices with electric power in addition to data connection over a single twisted-pair Ethernet cable. This solution works as a combination of a device that supports Power over Ethernet, a cable, and a PoE network switch. Although it is possible to use a normal switch instead, a PoE injector would then be necessary between it and the device. This injector would be required to have its own main power connection.
How does it work?
Ethernet cables comprise twisted pairs of copper wires. Some of them transfer data, while others help to carry electric power. A portion of this power goes to the PoE switch or injector, and the rest is passed to the connected device.
Standardized techniques of transmitting power over Ethernet include Alternative A (Mode A), Alternative B (Mode B), and 4PPoE. Alternative A sends power and data on the same two of the four twisted pairs. In comparison, alternative B transports data over two pairs and power over the remaining two ones. On the contrary, 4PPoE employs all the pairs to deliver both power and data.