What is POE?
POE (power over Ethernet) refers to a technology of transmitting power through network cable. With the help of existing Ethernet, it can simultaneously transmit data and supply power to IP terminal equipment (such as IP phone, AP, IP camera, etc.) through network cable.
Poe is also known as power over LAN (POL) or active Ethernet, sometimes referred to as Ethernet power supply.
In order to standardize and promote the development of Poe power supply technology and solve the problem of adaptability between power supply and power receiving equipment from different manufacturers, IEEE standards committee has successively issued three Poe standards: IEEE 802.3af standard, IEEE 802.3at standard and IEEE 802.3bt standard.
Why do we need PoE?
Poe is a wired Ethernet power supply technology. The network cable used for data transmission has the ability of DC power supply at the same time, which can effectively solve the centralized power supply of terminals such as IP phone, wireless AP, portable device charger, card reader, camera and data acquisition. Poe power supply has the advantages of reliability, simple connection and unified standard:
- Reliable: a Poe device can supply power to multiple terminal devices at the same time, so as to realize centralized power supply and power backup at the same time.
- Simple connection: the terminal equipment does not need external power supply, but only one network cable.
- Standard: comply with international standards and use the globally unified RJ45 power interface to ensure the connection with equipment from different manufacturers.
How does PoE work?
The working process of the PoE system is as follows:
- Detection: The PSE device outputs a small voltage at the port until it detects that the cable terminal is connected to a power receiving device that supports the IEEE 802.3af standard.
- Classification: When the PSE detects a PD device that meets the requirements, it will further increase the output voltage to classify the PD device. Different levels correspond to different working powers.
- Power supply: After the classification is confirmed, the PSE device starts to supply power to the PD device from a low voltage until it provides stable and reliable DC power for the PD device.
- Power supply management: Provide stable and reliable DC power for PD devices, and it is also a process of continuous monitoring of PoE power supply.
- Power failure: If the PD powered device is disconnected from the network cable, the PSE power supply device will quickly stop power supply and re-detect whether the cable terminal is connected to the powered device.