Brocade Communications Systems FastIron, Руководство администратора, Страница: 342 / 388

FIGURE 10
PoE autodiscovery
PoE autodiscovery is a detection mechanism that identifies whether 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 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, PoE+, or PoH 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 power-sourcing equipment. When
a valid PD is detected, the Brocade PoE device performs power classification by inducing a specific
voltage and measuring the current consumption of the PD. Depending on the measured current, the
appropriate class is assigned to the PD. PDs that do not support classification are assigned a class of
0 (zero). The following table shows the different power classes and their respective power
consumption needs.
PoE autodiscovery
342 FastIron Ethernet Switch Administration Guide
53-1003625-01