Power over Ethernet(PoE), which allows a single Ethernet cable to provide both data connection and electric power to devices. The benefits of PoE are numerous from both a network efficiency standpoint as well as a cost standpoint.
The techniques of PoE have been standardized by the Institute of Electrical and Electronic Engineers (IEEE). In 2003, the first PoE standard 802.3af has approved defining the technology.
IEEE standards specify the maximum power output from PSE (Power sourcing equipment) and the power budget from PD (Powered device)
However, with recent technological developments and high wattage products come out, the insufficient amount of feeding power limiting the applications of PoE. For the reason, IEEE released standard 802.3at in 2009 and 802.3bt in 2018.
When a PD connect to PSE, the PSE can know how much power is required to operate the PD as long as the PD displays the classification signature. This means for PSE, the limited total power budget can be allocated effectively.
