Power over Ethernet (PoE)

Power over Ethernet (PoE) is a technique for delivering power to devices over copper Ethernet cabling, eliminating the need for separate power supplies and outlets. While PoE doesn't add Ethernet data capabilities, it does offer expanded options for how and where Ethernet end devices can be placed.

IEEE Standard	Type	Power Budget
IEEE 802.3af / PoE	Type 1	15.4W
IEEE 802.3at / PoE+	Type 2	30.8W
IEEE 802.3bt / UPoE	Type 3	60W
IEEE 802.3bt / UPoE+	Type 4	90-95W

Power Budget is how much power is leaving the Switch, not how much power the device is receiving! Power might dissipate in heat.

PSE & PD

• PSE (Power Sourcing Equipment): The device that is pushing power over the wire, like a Switch

• PD (Powered Device): The device that is being powered, for example an IP Camera or an IoT device

PoE Detection and Negotiation

PoE uses a technique to determine if PoE is connected to a PD or not, and how much power the PD requires.

1. PSE outputs a small amount of power to detect if there is any resistance. So, power is gonna go out and is gonna check if power comes back on a separate wire.

2. PDs have a special resistor in the NIC that will respond and reflect back a certain amount of power to PSE.

3. PSE now knows it is connected to a PD, and, depending on the voltage it receives back, performs this step a few more times to detect the type and classification of PD.

4. PSE now knows how much power to deliver!