Brocade FastIron Ethernet Switch Administration Guide - Manual (Page 264)

The Midspan method is illustrated in the figure below.
FIGURE 10 PoE Midspan delivery method
PoE autodiscovery
PoE autodiscovery is a detection mechanism that identifies whether or not an installed device is
802.3af- or 802.3at-compatible. When you plug a device into an Ethernet port that is capable of
providing inline power, the autodiscovery mechanism detects whether or not the device requires power
and how much power is needed. The autodiscovery mechanism also has a disconnect protection
mechanism that shuts down the power once a PD has been disconnected from the network or when a
faulty PD has been detected. This feature enables safe installation and prevents high-voltage damage
to equipment.
PoE autodiscovery is achieved by periodically transmitting current or test voltages that can detect
when a PD is attached to the network. When an 802.3af- or 802.3at-compatible device is plugged into
a PoE or PoE+ port, the PD reflects test voltage back to the power sourcing device (the Brocade
device), ultimately causing the power to be switched on. Devices not compatible with 802.3af do not
reflect test voltage back to the power sourcing device.
Power class
A power class determines the amount of power a PD receives from a PSE. When a valid PD is
detected, the Brocade PoE device performs power classification by inducing a specific voltage and
PoE autodiscovery
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