The Power over Ethernet standard defines two methods for the use of an Ethernet transmission cable for DC transmission to POE compatible devices:
1,the middle span method. Use an independent PoE power supply device to connect between the outdoor PoE switch and the PoE enabled terminal equipment. The use of an idle line pair that is not used in the Ethernet cable to transmit direct current.
2, the end of the cross method. The PoE injector is integrated into the outlet of the signal in the switch, and the integrated connection is provided with the functions of an idle line pair and a data line pair.