POE Switch Working Process

- Feb 24, 2019-

When a POE switch is deployed in a network, the POE switch works as follows:

Detection: At first, the poe switch outputs a small voltage on the port until it detects that the cable terminal is connected to a powered-end device that supports the IEEE802.3af standard.

PD end device classification: After detecting the power receiving device PD, the poe switch may classify the PD device and evaluate the power loss required by the PD device.

Start of power supply: During a configurable time (typically less than 15μs), the poe switch begins to supply power from the low voltage to the PD device until 48V DC power is supplied.

Power supply: Provides stable and reliable 48V DC power for PD devices, which can meet the power consumption of PD devices not exceeding 15.4W.

Power failure: If the PD device is disconnected from the network, the poe switch will stop powering the PD device quickly (usually within 300~400ms) and repeat the detection process to detect whether the cable terminal is connected to the PD device.


A complete POE system includes two parts: a Power Sourcing Equipment (PSE) and a Powered Device (PD). The Poe switch is a PSE device. The PSE device is a device that powers Ethernet client devices and is the administrator of the entire POE Power over Ethernet process. The PD device is the PSE load that receives power, that is, the client of the POE system.