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HP ProCurve 2520 Planning And Implementation Manual: Poe Capabilities Of The Products

Procurve power over ethernet (poe/poe+).
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PoE Capabilities of the Products

An obvious requirement of the specification is to prevent damage to existing
Ethernet equipment. A discovery process, run from the PSE, examines the
Ethernet cables, looking for devices that comply with the specification. It does
this by applying a small current-limited voltage to the cable and checks for the
presence of a 25k ohm resistor in the remote device. Only if the resistor is
present, will the full wattage be applied, but this is still current-limited to
prevent damage to cables and equipment in fault conditions.
Once discovered, a different voltage is applied, and based upon the current
drawn, the class of device can be determined. This indicates how much power
is to be drawn. The 802.3at standard provides both a physical classification
and a logical classification, which is even more precise.
The PD must continue to draw a minimum current. If it does not (for example,
when the device is unplugged) then the PSE removes the power and the
discovery process begins again.
PoE Capabilities of the Products
These switches are designed to be used primarily in wiring closets directly
connected to computers, printers, and servers to provide dedicated
bandwidth to those devices. Additionally, they support the PoE standard IEEE
802.3af, and the PoE+ IEEE 802.3at standard. They can supply power over a
twisted-pair cable to power devices such as telephones, wireless access
points, IP Gateways, and audio and video remote monitoring.
The HP ProCurve PoE switch devices are multi-port switches that can be used
to build high-performance switched workgroup networks with PoE. These
switches are store-and-forward devices that offer low latency for high-speed
networking. The PoE switches are designed to support Redundant Power
Supply and Power over Ethernet (PoE and/or PoE+) technologies.


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