Specifications

Power
93
There are two methods of providing power in the standard:
• “Phantom” power across existing Ethernet wires (RJ-45 pins 1, 2, 3 and 6). This is the
method typically used by 802.3af compliant Ethernet switches. The 3300 CXi controller
uses the phantom (signal pair) method for delivering power.
• “Spare pair” power where power is supplied across RJ-45 pins 4, 5, 7 and 8. This is the
method typically used by mid-span devices that sit between a non- 802.3af Ethernet switch
and the end device.
Devices that provide power by either method are called are called “Power Sourcing Equipment”
(PSE) and devices that accept the power are “Powered Devices” (PD). MiVoice IP Phones are
Powered Devices. Some Mitel phones also accept local powering options. For more information,
see Table 33, “IP Phone Power Options,” on page 90.
The standard requires that a “signature” be detected on an PSE port prior to applying significant
power on the cable. Regular PC NICs do not have this signature, whereas MiVoice IP Phones do.
A Power over Ethernet port produces current limited, low voltage pulses which allow it to probe
for a particular impedance at the end of the Ethernet cable. If this “signature” is detected (an
IP Phone, for example), then the PSE assumes that power is required. If the “signature” is not
detected (e.g. PC NIC), then the PSE does not apply power.
Once the “signature” or impedance has been detected, the voltage is increased and current
draw is monitored. The amount of current drawn allows the PSE to classify the device for Power
over Ethernet requirements. Classification is an optional part of the standard and allows the
end device to “inform” the PSE of its power requirements. It is only performed on initial power up.
• Class 0 is the default. Devices that do not support the optional classification will default to
this setting. Class 0 requests the PSE to provide 15.4 Watts of power.
• Class 1 requests the PSE to provide a maximum of 4 Watts.
• Class 2 requests the PSE to provide a maximum of 7 Watts.
• Class 3 requests the PSE to provide 15.4 Watts (like Class 0), however, the PD will always
draw at least 7 Watts or more.
Power required for MiVoice IP Phones is fairly constant whether in use or sitting idle. Very loud
ringer and hands-free settings can draw more power than normal. Also, additional devices
connected to the IP Phone such as a PKM, a LIM and a Conference Unit increase the power
required by the IP phone. For details on optional device power requirements refer to “Power
Requirements for 5220 IP Phone Optional Accessories” on page 108.
Table 36, “802.3af Power Class Advertisements,” on page 101 can be used to determine which
Class a particular phone advertises.
3300 CXi/CXi II ICP 802.3af Power over Ethernet capabilities
The CXi/CXi II includes a 16-port managed Layer 2 Ethernet switch. The 16 Ethernet ports
comply with the 802.3af Power over Ethernet (PoE) specification, which enables them to deliver
power to IP phones and other Ethernet devices over Category 3 or 5 cabling.
Note: Mitel phones can be powered from equipment that uses phantom powering or
spare pair powering.