Power Over
Ethernet
Power
Over Ethernet (PoE)
technology describes any system that transmits electrical power,
in addition to data, to remote devices over standard
twisted-pair wire in an Ethernet network. This technology is
useful for powering network devices where it would be
inconvenient or infeasible to supply power separately. Such
devices include IP telephones, wireless LAN access points,
IP cameras, IP sensors and instruments in industry, IP radios,
digital clocks, and more. The technology
is comparable to POTS telephones, which also receive power and
data (although analog) through the same cable.
PoE
works without requiring modification to the existing Ethernet
copper cabling infrastructure. Power over Ethernet is
standardized in IEEE 802.3af. The IEEE 802.3af-compliant
power sources supply 48 volts DC to devices at a maximum current
of 350 mA. This allows devices to draw up to 15.4 watts.
A
twisted-pair Ethernet cable contains four pairs of wires. The
Ethernet RJ-45 10/100Mb twisted-pair cable standard uses two of
these pairs for data. The 802.3af standard allows power
transmission over the two unused pairs, or the two data pairs.
To prevent damage to devices that don't accept power over
Ethernet, an 802.3af power source won't begin sending power
until a remote device acknowledges that it can accept power.
(Ref. Wikipedia)
A
Position Paper by GarrettCom:
Power Over Ethernet - The
Industrial Opportunity Today
The
Magnum
PS14P is a 4-port PoE heavy
duty Ethernet Switch for Industrial PoE applications.
For
AC to -48V DC industrial power supplies, go to www.LANstore.com
and look for model ML50.105.
More general information on Power Over Ethernet, see web
sites such as:
www.PowerOverEthernet.com
http://www.altair.org/labnotes_POE.html
http://www.vdc-corp.com/power/reports/05/br05-14research.pdf
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