WHAT IS POE

In simple terms, the POE(Power Over Ethernet) is a method that uses network cables to supply power to network terminals. In this way, the problem that internet terminals’power supply issue is easily solved,save the cost of settle power cord.

What Is Its Feature ?

The POE technology ensures the security of the existing structured cabling and the normal operation of the existing network, minimizing the cost. IEEE 802.3AF is a new standard based on POE. It adds a related standard of direct power supply through network cable on the basis of IEEE 802.3AF. It is an extension of the existing Ethernet standard and the first international standard on power distribution.

System Composition of POE:

A complete POE system includes two parts: power supply equipment (PSE) and power receiving device (PD). The PSE device is the device that powers the Ethernet client device and the manager of the entire POE Ethernet power supply process. The PD device is the PSE load that receives power, that is, the client devices of the POE system, such as IP phones, network security cameras, AP, and many other Ethernet devices such as PDA or mobile phone chargers (in fact, any device with up to 13W of power can draw the corresponding power from the RJ45 socket). Based on IEEE 802.3AF standard, they establish information relation about the connection condition, device type, power consumption level and other aspects of the PD of the receiving end, and supply power to PD through Ethernet according to PSE.

Power Supply Working Process

1. Check: At first, the POE device outputs a small voltage over the port until it detects that the cable terminal is connected to a power receiving device that supports IEEE802.3AF.

2. Classification of PD devices: After detecting PD on the receiving device, the POE device may classify the PD devices and evaluate the power loss required by the PD devices.

3. Start power supply: The PSE device starts supplying power to the PD device from a low voltage until it provides 48V DC power during a start period of a configurable time (generally less than 15μs).

4. Power supply: to provide stable and reliable 48V DC for PD equipment, to meet the power consumption of PD equipment does not exceed 15.4W.

5. Power off: If the PD device is disconnected from the network, PSE will quickly (generally within 300 ~ 400ms) stop supplying power to the PD device, and repeat the detection process to check whether the terminal of the cable is connected to the PD device.

Power Supply Method

The POE standard defines two methods for delivering DC to POE-compatible devices using Ethernet transmission cables:

(1)Mid-Span Method

In mid-span, an independent PoE power supply device is connected between the switch and the terminal with the PoE function. Generally, the idle pair of Ethernet cables is used to transmit DC. The Mid-span PSE is a specialized power management device, usually placed with a switch. Each port has two RJ45 jacks. One is connected to the switch (a traditional switch without PoE function) by a short cable, and the other is connected to a remote device.

(2）End-Span Method

Another approach is the "end-span" method, which integrates the power supply device at the outlet of the signal in the switch. Such integrated connections generally provide "dual" power supply for both free and data line pairs. The signal isolation transformer is used in the data line pair, and the DC power supply is realized by using the center tap. It can be expected that End-SPAN will be rapidly popularized. This is because Ethernet data and transmission use common line pairs, thus eliminating the need to set up a separate transmission line, which is especially significant for only 8-core cables and the matching standard RJ-45 socket.

Latest Developments

PowerDsine, a maker of power over Ethernet chips, will hold an IEEE conference to formally submit its "Power Over Ethernet" standard, which will support powering devices such as laptops. PowerDsine will submit a white paper proposing to double the 802.3AF standard's 48V input, 13W usable power limit. In addition to laptops, the new standard could power things like liquid crystal displays and video phones.

IEEE has released a new 802.3AT, which stipulates that POE can provide higher power, beyond 13W, up to 30W.