POE is short for Power over Ethernet. POE is a technology that transmits data signals for some IP-based terminals (such as IP intercom telephones, wifi wireless LAN access points (AP), and webcams) without any changes to the existing Ethernet Cat.5 cabling infrastructure, and also provides DC power for such devices.PoE technology can ensure the security of the existing structured cabling, ensure the normal operation of the existing network, and minimize the cost.
PoE, also known as PoL (Power over LAN) or Active Ethernet, and sometimes simply referred to Power over Ethernet, is the latest standard specification for simultaneously transmitting data and electrical power using existing standard Ethernet transmission cables， and maintain the compatibility with existing Ethernet systems and users. The IEEE 802.3af standard is a new standard based on PoE. It adds the related standard of direct power supply over network routes on the basis of IEEE 802.3AF. It is an extension of the existing Ethernet standard and also the first international standard on power supply distribution.
IEEE began developing the standard in 1999, with the earliest participants being 3Com, Intel, PowerDsine, Nortel, Mitel, and National Semiconductor. However, the shortcomings of the standard have been limiting the expansion of the market. Until to June 2003 that IEEE approved the 802.3af standard, which specifies power detection and control matters in remote systems. It also regulates how routers, switches, and hubs can supply power over Ethernet cables to devices such as IP phones, security systems, and wireless LAN access points. The development of IEEE 802.3af has involved the efforts of experts from many companies, which has allowed the standard to be tested in many ways.
A typical Ethernet power supply system
Keep the Ethernet switch equipment in the distribution cabinet and use a Midspan HUB with power supply to power the twisted pair cables on the LAN. At the end of the twisted pair, the power supply is used to drive phones, wireless access points, cameras and other devices. The user can use a UPS to power-on the device to avoid power outages.
PoE principle
The standard Cat.5 Class 5 network route has four pairs of twisted pairs, but only two of them are used in 10M BASE-T and 100M BASE-T. Two usages of IEEE80 2.3af are allowed. When space pin power is applied, pin 4 and 5 are connected as positive terminals, and pin 7 and 8 are connected as negative terminals. When the data pin is used for power supply, the DC power supply is added at the midpoint of the transmission transformer without affecting the data transmission. By this way,
line pairs 1 ,2 and line pairs 3, 6 can be of any polarity . This standard does not allow both cases to be applied simultaneously. The power supply device PSE can only provide one use, but the power application device PD must be able to accommodate both situations. The standard specifies that the power supply is usually 48V, 13W. PD devices provide easily conversion from 48V to low voltage,but at the same time there should be 1500V insulation safety voltage.
PoE Parameter
A complete PoE system includes PSE( Power Sourcing Equipment) and PD(Powered Device) two parts. The PSE is the device that power the Ethernet client devices and the manager of the entire PoE Ethernet power process. The PD device is the PSE load that receives the power supply, they are the client device of the POE system, such as IP phone, Webcam, AP , PDA , mobile phone chargers or many other Ethernet devices( Any device with a power of up to 13W can obtain the corresponding power from the RJ45 socket). The two are based on IEEE 802.3af standard to establish the connection, device type, power consumption level and other aspects of the receiving device PD, and use this to supply power to PD through Ethernet according to PSE. The power supply characteristics of the POE standard power supply system are as follows:
- The voltage is between 44 and 57V, with a typical value of 48V.
- The maximum allowable current is 550mA and the maximum starting current is 500mA.
- Typical operating current is 10 ~ 350mA, overload detection current is 350 ~ 500mA.
- Under no-load conditions, the maximum required current is 5mA