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9. Power over Ethernet (PoE) Commands
This chapter contains the following sections:
• About PoE
• PoE Commands
About PoE
Power over Ethernet describes a technology to pass electrical power safely along with data
on existing Ethernet cabling. The PSE or power supply equipment is the device or switch that
delivers electrical power, and the PD or powered device is the end device that powers up
through the power delivered along the Ethernet cable.
This technology is governed by two standards:
• IEEE 802.3af-2003. This is the original standard, also known as the low-power standard,
which mandates delivery of up to 15.4 watts by the PSE. Because of power dissipation,
only 12.95 watts are assured to be available at the powered device (PD). The PD needs
to be designed so that it can accept power over Ethernet cabling. Category 3 cables can
be used to deliver power to the PD. However, with the advent of 802.11n, the newer
wireless APs required more power. To account for this, a newer standard was developed
in 2009, known as 802.3at.
• IEEE 802.3at-2009. This is the newer standard, also known as PoE+. This is also known
as the high-power standard, which mandates delivery of up to 34.2 watts by the PSE.
Because of power dissipation, PoE+ provides only a maximum of 25.5 watts at the
powered device. Some PSEs can provide up to 51 watts. Before this standard became
available in 2009, the industry started using different implementations to allow for more
power. All these needed to be brought under the purview of the newer 802.3at standard.