Configuration Guide User guide
662 FastIron Configuration Guide
53-1002494-02
Power over Ethernet overview
FIGURE 60 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
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). Table 122 shows the different power classes and their respective power consumption
needs.
PoE Midspan Delivery Method
Switch
Intermediate device
IP phone
Power travels on unused spare
pairs while data travels on other
wire pairs.
CONSOLE
POWER
PS1
PS2
ACT
LINK
49F 50F
49C
50C
125234 6 11789101
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484138 39 40 42 4743 44 45 4637362926 27 28 30 3531 32 33 3425
FastIron Edge 4802 POE