POE is also called power over LAN (POL) or Active Ethernet, and is sometimes referred to simply as Ethernet power supply. It is the latest standard specification for transmitting data and electric power simultaneously by using existing standard Ethernet transmission cables, and maintains compatibility with existing Ethernet systems and users. The IEEE 802.3af standard is a new standard based on POE, which adds the related standard of direct power supply through network cable to IEEE 802.3. It is an extension of the existing Ethernet standard and the first international standard on power distribution.

IEEE 802.3af

IEEE began to formulate the standard in 1999, and the earliest participating manufacturers were 3Com, Intel, Powerd Sine, Nortel, Mitel and National Semiconductor. However, the shortcomings of this standard have been restricting the expansion of the market. Until June, 2003, IEEE approved the 802. 3af standard, which clearly stipulated the matters of power detection and control in remote systems, and stipulated the way that routers, switches and hubs supplied power to IP phones, security systems and wireless LAN access points through Ethernet cables. The development of IEEE 802.3af includes the efforts of many company experts, which also enables the standard to be tested in all aspects. A typical Ethernet power supply system. Keep the Ethernet switch equipment in the wiring cabinet, and use a power supply hub (Midspan HUB) to provide power for the twisted pair of LAN. At the end of twisted pair, the power supply is used to drive telephones, wireless access points, cameras and other devices. To avoid power failure, you can choose a UPS.

System composition and power supply characteristic parameters of POE

A complete POE system includes two parts PSE, Power Sourcing Equipment (PSE) and power receiving equipment (PD). PSE equipment is the equipment that supplies power to Ethernet client equipment, and it is also the manager of the whole POE Ethernet power supply process. The PD equipment is a PSE load that receives power supply, that is, the client equipment of POE system, such as IP phone, network security camera, AP, PDA or mobile phone charger, and many other Ethernet devices (in fact, any equipment with power less than 13W can get corresponding power from RJ45 socket). Based on IEEE 802.3af standard, they establish the information connection about the connection, equipment type, power consumption level and other aspects of the receiving terminal equipment PD, and supply power to PD through Ethernet according to PSE. The main power supply characteristic parameters of POE standard power supply system are as follows: 1. The voltage is between 44 and 57V, with a typical value of 48V. 2. The maximum allowable current is 550mA, and the maximum starting current is 500mA. 3. The typical working current is 10 ~ 350 Ma, and the overload detection current is 350 ~ 500 Ma. 4. Under no-load condition, the maximum required current is 5mA. 5. Provide PD equipment with five levels of electric power requirements of 3.84 ~ 12.95 W, with a maximum of 13 W..

Working process of POE power supply

When the PSE power supply terminal equipment is arranged in a network, the working process of POE Ethernet power supply is as follows. 1. At the beginning of detection, the PSE device outputs a small voltage at the port until it detects that the cable terminal is connected to a power receiving terminal device supporting the IEEE 802.3af standard. 2. Classification of PD-side equipment After detecting the PD at the receiving end, the PSE equipment may classify the PD equipment and evaluate the power consumption required by this PD equipment. 3. Start power supply During the start-up period of a configurable time (generally less than 15μs), PSE equipment starts to supply power to PD equipment from low voltage until 48V DC power supply is provided. 4. Power supply provides stable and reliable DC power of 48V for PD equipment, and meets the power consumption of PD equipment not exceeding 15.4W. 5. Power failure If the PD device is disconnected from the network, PSE will quickly stop supplying power to the PD device (generally within 300 ~ 400 ms) and repeat the detection process to detect whether the terminal of the cable is connected to the PD device.

The principle of POE supplying power through cable

There are four pairs of twisted pairs in the standard five-class network cable, but only two of them are used in l0M BASE-T and 100m BASE-T.. IEEE80 2.3af allows two usages. When the idle pin is used for power supply, pin 4 and pin 5 are connected as the positive electrode, and pin 7 and pin 8 are connected as the negative electrode. When the data pin is used for power supply, the DC power supply is added to the midpoint of the transmission transformer, which does not affect the data transmission. In this way, pairs 1 and 2 and pairs 3 and 6 can be of any polarity. The standard does not allow the above two situations to be applied at the same time. Power supply equipment PSE can only provide one usage, but power supply application equipment PD must be able to adapt to both situations at the same time. The standard stipulates that the power supply is usually 48V and 13W. It is easy for PD equipment to provide the conversion from 48V to low voltage, but at the same time it should have an insulation safe voltage of 1500V.

Two power supply methods of POE

POE standard defines two methods for using Ethernet transmission cables to transmit DC power to POE-compatible devices: Mid -Span method uses unused pairs of Ethernet cables to transmit DC power, which is applied between ordinary switches and network terminal devices, and can supply power to network terminal devices through network cables. Mid-span PSE (Mid-span Power Supply Device) is a special power management device, which is usually placed with switches. It has two RJ45 jacks corresponding to each port, one is connected to the switch with a short wire, and the other is connected to a remote device. End-Span method is to transmit direct current at the same time on the core wire used for data transmission, and its transmission frequency is different from that of Ethernet data signal. The corresponding Endpoint PSE (terminal power supply equipment) has an Ethernet switch, router, hub or other network switching equipment that supports POE function. It can be predicted that End-Span will be popularized rapidly, because Ethernet data and power transmission adopt public wire pairs, thus eliminating the need to set up special wires for independent power transmission, which is particularly significant for cables with only 8 cores and matching standard RJ-45 sockets.

develop

PowerDsine, an Ethernet power supply chip manufacturer, will hold an IEEE conference to formally submit the standard of "High Power Ethernet Power Supply", which will support the power supply for notebook computers and other devices. PowerDsine will submit a white paper, proposing to double the available power limit of 48v input and 13w of 802.3af standard. In addition to notebook computers, the new standard may also provide power for LCD monitors and video phones. Recently, IEEE released the latest 802.3AT, which stipulates that POE can provide higher power, exceeding 13W and reaching 50W!