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POE (Power Over Ethernet)
POE (Power over Ethernet) refers to the existing Ethernet cabling infrastructure under 5 class does not make any changes, for some IP-based terminals (such as IP phones, wireless LAN access point AP, network cameras, etc.) to transmit data while the signal, but also to provide DC power supply such equipment technology. POE technology to ensure the normal operation of the existing network to ensure the safety of the existing structured cabling while minimizing costs.
Power is also known as LAN-based power supply system (POL, Power LAN) or Active Ethernet (Active Ethernet), sometimes referred to as Power over Ethernet, which is using the existing transmission standard Ethernet cable to transfer data at the same time and The latest standard of the electric power, and maintain compatibility with existing Ethernet systems and users. Ethernet standard IEEE 802.3af POE power supply system is based on the new standards, which increases the standard power through the network cable directly to the relevant IEEE 802.3, based on the extension of the existing Ethernet standards, is the first international match electrical standards.
IEEE standards developed in 1999, the first participating vendor 3Com, Intel, PowerDsine company, Nortel, Mitel and National Semiconductor. However, the disadvantage of this standard has been to limit the expansion of the market. Until June 2003, IEEE 802 3AF approved standards, clearly defined power detection and control remote systems issues, as well as routers, switches and hubs via Ethernet cable is connected to the IP phones, security systems and wireless LAN access points and other equipment Power has been prescribed manner. Experts from many companies included in the IEEE 802.3af standard, which makes it possible to be tested in all aspects of the standard effort.
 
Whether it is to buy the most simple Ethernet switch or wireless AP router, accessories include a square head brain, stupidity and AC power transformers (commonly known as power) of crude, inconvenient to use. It is possible to make a two-wire transmission signal, and provides it?
Our lives have similar examples, such as our family ordinary fixed telephone, no additional power supply, power can even call home, because the telephone lines can transmit not only voice signals, but also responsible for the power supply to the phone (smartphone power increase large Sometimes the need for additional power supply). Such PoE (Power over Ethernet Power over Ethernet) technology came into being.
The PoE (Power over Ethernet, called POE), also known as PoE power supply, is a to transmit power and data to the device via twisted pair Ethernet technology in the road. Power over Ethernet starting point is to make IP phones, WLAN access points, network cameras, small network equipment, you can get the power (four pairs of two pairs of twisted pair transmission idle) directly from the Ethernet cable, the need for a separate power line laying, to simplify system cabling, network infrastructure, reduce project cost.
 
Specification
In order to standardize and promote the development of PoE applications, in June 2003, IEEE 802.3 Working Group to develop a standard Ethernet IEEE 802.3af power standard network expansion, send and receive have done a detailed provisions.
Ethernet standard IEEE 802.3af POE power supply system is based on the new standards, which increases the standard power through the network cable directly to the relevant IEEE 802.3, based on the extension of the existing Ethernet standards, is the first international match electrical standards.
IEEE standards developed in 1999, the first participating vendor 3Com, Intel, PowerDsine company, Nortel, Mitel and National Semiconductor. However, the disadvantage of this standard has been to limit the expansion of the market. Until June 2003, IEEE 802 3AF approved standards, clearly defined power detection and control remote systems issues, as well as routers, switches and hubs via Ethernet cable is connected to the IP phones, security systems and wireless LAN access points and other equipment Power has been prescribed manner. Experts from many companies included in the IEEE 802.3af standard, which makes it possible to be tested in all aspects of the standard effort.
October 2009, IEEE 802.3at standard terminal electricity demand should be born in a compatible 802.3af standard, based on the greater power requirements, to meet the new demands.
 
Principle
 
Standard UTP cable has four pairs, but in 10M BASE-T and 100M BASE-T is used only in a two pair. IEEE80 2.3af allow two uses, foot-powered when the application is idle, as a positive electrode, a negative electrode 7-8 pin connector 4 and 5-pin connector.
When data-pin power applied to the midpoint of the transformer DC power transmission, it does not affect the transmission of data. In this way offline 1,2- and 3,6 for either polarity.
Standard does not allow the above-mentioned two cases also apply. PSE-powered devices offer only one usage, but the power PD applications must be able to adapt to the two cases. This standard specifies the power supply is usually 48V, 13W of. The PD device provides 48V to low-voltage conversion is relatively easy, but at the same time there should be insulated 1500V safety voltage.
 
Parameters
 
POE system consists of two parts of a complete supply terminal equipment (PSE, power supply equipment) and the receiving end device (PD, Powered Device) power supply. PSE device Ethernet client devices powered devices, as well as Power over Ethernet POE management of the whole process. The PD device powered PSE load after acceptance, the client device that is POE systems, such as IP telephony, network security cameras, AP and Pocket PC (PDA) or mobile phone chargers and many other Ethernet devices (in fact, any power No more than 13W from the RJ45 interface device corresponding power). The two sides to establish the appropriate connection, device type, power level, and other basic contact IEEE 802.3af standard PD electrical equipment, and as Power over Ethernet according to PSE by PD.
POE standard main power system parameters are as follows:
1. Voltage between 44~57V, typical values ​​of 48V.
2. The maximum permissible current of 550 mA, 500mA current maximum starting current.
3. Typical operating current is 10~350mA current overload detection current 350~500mA current.
4. Under no-load conditions, the required maximum current of 5mA.
5. Provide 3.84~12.95W three levels of PD device power requirements, maximum of 13W. (Note PD 0-level and four did not appear, should not be used.)
 
Working Process
 
When PSE power supply terminal device is arranged in a network, POE Power over Ethernet works as follows.
1. Detection
A beginning, PSE device port output low voltage cable terminal until it detects a support IEEE 802.3af standard powered device is connected to the terminal.
2. PD Premises Equipment Category
When the receiving end device detects the PD, PSE device can be classified as PD, and PD devices need to evaluate this power loss.
3. Start Power
A configurable time (generally less than that of 15μs) during startup, PSE equipment from low voltage power supply began to PD device, providing up to 48V DC power supply.
4. Power
In order to provide a stable and reliable 48V DC to the PD device that does not meet the power consumption of 15.4W across PD.
5. Close
If the PD device is disconnected from the network, PSE will quickly (usually 300~400 ms) function to stop power supply devices, and duplicate detection process to detect cable terminal connector PD devices.
 
Power Supply Method
 
For transmission cable DC POE compatible transport equipment PoE Ethernet standard defines two methods:
Intermediate bridging method (in -span)
Use an Ethernet cable is used to transmit an idle line is not on the DC switching network terminal equipment used in general and between, you can give power network terminal equipment, intermediate PSE (Cross-powered devices) via a network cable is a dedicated power management devices, usually switches together. It corresponds to each port has two RJ45 jacks to connect to the switch with a short, another to connect the remote device.
 
Cross-end connection (End Span)
HVDC transmission is simultaneously used wire data, Ethernet data signals of different frequencies transmitted. Appropriate endpoint PSE (End power equipment), supports POE function Ethernet switch, router, hub or other network switching equipment. It is foreseeable that end cross will quickly upgrade, using ordinary pairs, thus eliminating the need for a separate dedicated transmission line, which is only 8-core cable and supporting the standard RJ-45 jack This is due in particular Ethernet data transmission significant.
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