The specification for PoE calls for two devices: the power source equipment (PSE) (POE data switch) and the powered device (PD) (IP phone, WAP, IP camera, IP speaker). When power over Ethernet (POE) IEEE 802.3af was ratified in 2003, its nominal power delivery at 12.95 Watts of DC power was more than adequate for the early adopter applications such as your standard VoIP phones, security cameras, and wireless access points (WAPs). In 2003, the IEEE 802.3af standard for Power over Ethernet introduced a new aspect to Ethernet data networking, it allow for the delivery of DC power in tandem with the 10/100/1000 Mbps data. Only 12.95 W is assured to be available at the powered device as some power is dissipated in the cable The original IEEE 802.3af-2003 PoE standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA) to each device. In the case of PoE devices, power class is also reported. Powered Devices (PD) are discovered using Link Layer Discovery Protocol ( LLDP) which is a vendor-neutral Link Layer protocol in the Internet Protocol Suite used by network devices for advertising their identity, capabilities, and neighbors on a IEEE 802 local area network, principally wired Ethernet.
This article will primarily focus on standard PoE implementation.
PoE can be utilized with EtherCAT technology such a Keyboard Interface Adapter and in addition there is EtherCAT P, which is a PoE infrastructure build specifically for use with EtherCAT. It can come from a power supply within a PoE-enabled networking device such as an Ethernet switch or can be injected into a cable run with a midspan power supply. Power is supplied in common mode over two or more of the differential pairs of wires found in the Ethernet cables. The IEEE standard for PoE requires Category 5 cable or higher for high power levels, but can operate with category 3 cable for low power levels. Power over Ethernet or PoE technology describes a system to pass electrical power safely, along with data, on Ethernet cabling.
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