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Power Over Ethernet Standards

Power Over Ethernet Standards

IEEE 802.3 is the standard that defines the physical layer of Ethernet cabling. It includes wire type, signal level and bandwidth in 2003, the standard was updated to include PoE IEEE 802.3af defines the voltage and power availability of devices on a network. The specification provides PoE with up to 15.4 watts of power. The specification was updated again in 2009. The IEEE 802.3 at provides higher power (25.5 watts), called PoE +.

The IEEE-compliant PoE injector provides 44 to 57 volts. The effective distance of the cable is the same as the standard ethernet distance of 100 meters (328 feet). There are two modes, A and B, for powering devices. These modes define the polarity of the wire pair and the voltage used for the power supply. The new PoE injector can provide more than 50 watts of power to a network-connected device. These higher power Ethernet devices use two pairs of wires to transmit power to the device.

802.3af (2003)
  • Power Sourcing Equipment (PSE) transmitted a maximum of 15.4W which assured delivery of 12.95W (350mA) to the Powered Device (PD).
  • Total throughput was limited to 100Mbps and allowed power to be distributed over only two pairs, and in two different modes (Mode A and Mode B) as seen in Figure 1 below.

Figure 1

IEEE 802.3at (2009)
  • Power Sourcing Equipment (PSE) transmitted a maximum of 30W which assured delivery of 25.5W (600mA) to the Powered Device (PD).
  • Total throughput was limited to 1000 Mpbs or 1Gbps.
  • The same Mode A and Mode B were used again, and the same pairs are used to transmit power. The difference with 802.3at is that all four pairs are used to transmit data packets to achieve 1Gbps throughput (Figure 2).

Figure 2
IEEE 802.3bt (2018)
  • Two power levels emerging: Version 1 - 60W from Power Sourcing Equipment (PSE) and 50W assured at Powered Device (PD) side. Version 2 - about 100W from PSE and about 80W assured at PD side.
  • All four pairs will transmit data packets and power.
  • Total throughput will be 10Gbps, a 10x increase over previous generations.
  • Backwards compatible with previous generations of PoE; 802.3af and 802.3at.
  • Figure 3 illustrates a proposed 4-pair power delivery solution.

Figure 3
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