IEEE poe 802. 3 at: POE (Power over Ethernet) is a kind of LAN technology, which can provide DC power to the powered device through twisted pair. It has been widely used in enterprises and industrial applications. According to statistics, in 2006, the Ethernet power supply delivery volume was 32 million ports. By 2011, the delivery volume will be increased to 145 million ports, with an annual growth rate of more than 30%. The standard adopted by Poe industry is IEEE 802.3af, which stipulates that power supply equipment can supply power to the powered device with power below 13W through Ethernet. This is enough to meet the need of the traditional IP phones and webcams. However, with the emergence of dual band access, video phone, PTZ video monitoring system and other high-power applications, 13W power supply obviously can not meet the demand. Therefore, IEEE began to develop a new PoE standard 802.3at (POE plus) in 2005 to improve the power that PoE can transmit.
Compared with 802.3af, PoE 802.3 at can output more than twice the power, and the output power of each port can be more than 30W. Therefore, the application field of PoE can be greatly expanded. Table 1 shows the comparison between 802.3af and 802.3at. Although 802.3ats has not been officially launched, manufacturers in the industry began to launch devices that meet the pre－IEEE802.3at standard.