Power over Ethernet systems are seeing increasing use in today's society. Power over Ethernet, sometimes abbreviated PoE, refers to providing power to Ethernet devices over an Ethernet line that is also used to communicate data. Thus, power over Ethernet devices do not require separate power supply lines. In some instances, the power may be supplied by a power supply contained within an Ethernet switch. Because the power supply does not generally have the power capability to supply maximum power to every port, there is a limit on the number of power over Ethernet devices that can be connected to a given power supply. A port may be denied power, if it will result in oversubscription of the power supply. Example power over Ethernet devices that can benefit from receiving power over the Ethernet communication lines include an internet protocol telephone, a badge reader, a wireless access point, a video camera, and others.
Traditionally, when a power over Ethernet device is connected to a power supply, the power over Ethernet device is allocated a maximum power class according to IEEE standard 802.3af denoted as class 0 thru 4. These maximum values correspond to the maximum amount of power that will be supplied by the power supply to the power over Ethernet device. IEEE standard 802.3af provides for three levels of 15.4 watts, 7.5 watts, and 4.0 watts for these power over Ethernet devices. In certain circumstances, such allocation prevents the power supply from being utilized to its full capability due to the coarse granularity in class.
A software program referred to as Cisco Discovery Protocol allows for more granular specification of the limit for the power over Ethernet powered devices other than the above-described IEEE levels. However, the power supply still may have unutilized capacity.