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Detektor Security Academy is an educational concept in which Detektor
magazine, together with selected security technology leaders, have cooperated
to produce, distribute and promote essential information about the opportuni-
ties that today's security technology can offer.
In this article, sponsored by EtherWAN, Detektor Security Academy will
explain how Power over Ethernet (PoE) can save money, increase the security
level and simplify the installation of IP surveillance equipment. This is the fourth
article within Detektor Security Academy.
Sponsored by
SECURITY ACADEMY
Effective IP surveillance
with Power over Ethernet
PoE means passing electrical power
on Ethernet cabling, along with
data. The IEEE standard for PoE
requires Category 5 cable or higher
for high power levels.
detektor security
academy
360mA. The output voltage range
of IEEE 802.3af is from 44V DC
to 57V DC.
In 2010, IEEE ratified a new
PoE standard, 802.3at, which
provides 30W of DC power to
the PD. The maximum current
of IEEE802.3at is 600mA. The
output voltage range varies from
50V DC to 57V DC. The IEEE
802.3at standard is also known as
PoE+ or PoE plus.
The four Poe phases
Every PSE is responsible for man-
aging four basic aspects (or phases)
of PoE:
1. PD detection
2. PD classification
3. Power-up
4. Power-removal
PD detection and PD classifica-
tion are carried out through
complex signaling protocols which
make sure that power is delivered
to the PD according to the classifi-
cation. It prevents powering when
no PD is connected and assures
prompt power removal when a
PD is disconnected. The proto-
cols also maintain a stable DC
current flow at all voltage levels. A
PoE enabled PSE provides a low
power sourcing equipment (PSE)
and powered devices (PD). A
PD is a PoE enabled network
end device, such as an IP security
camera, equipped to accept low
voltage power transmitted over
Ethernet cabling.
A PSE on the other hand, is
a device that provides ("sources")
power to the Ethernet cable. Power
is supplied in common mode over
two or more of the differential
pairs of wires found in Ethernet
cables and comes from a power
supply such as an Ethernet switch.
There are two types of PSEs which
can add PoE to your network:
endspans and midspans. Endspans
are Ethernet switches that include
the power over Ethernet transmis-
sion circuitry and are commonly
called PoE switches. Midspans are
power injectors that stand between
a regular Ethernet switch and the
powered device, injecting power
without affecting the data.
Ieee standards
In June 2003, the IEEE working
group released the ratified IEEE
802.3af PoE standard. It provides
up to 15.4W of DC power
(minimum 44V DC and 350mA)
to each powered device. The maxi-
mum current of IEEE 802.3af is
mentation of a proprietary PoE
system was accomplished by Cisco
in the year 2000. Their technique
of putting 48V DC power on the
LAN data cable along with the
data traffic helped them overcome
their customer's objections to wall
adapter powering and in the end
also helped them to sell a lot of
VoIP phone systems.
This fourth article within
Detektor Security Academy will,
with the help of EtherWAN,
explain the most important facts
that everyone dealing with PoE
should know.
The Poe scheme
In a PoE scheme, two different
types of devices are involved:
Power over Ethernet, or PoE, is
not a new technology and it's
already widely utilised in network-
ing, for example in IP phones,
wireless AP's and IP cameras. The
first successful design and imple-
Effective IP surveillance
with Power over Ethernet
thepracticalknowledgeaboutPoEcompatibilityandqualitytesting
Power over ethernet technology describes a system
to pass electrical power over ethernet cabling, along
with data. This means that a network device can be
powered and operated using the same cable as for
network connection, eliminating the need for power
outlets close to an IP camera, for example. However,
in order to save money on installation and increase
the security level by using Poe, it's important to keep
certain key points in mind when dealing with the
technology. This article will guide you through equip-
ment and standards within Poe that will help you
succeed in the field.
A PoE enabled IP security camera is
an example of a powered device (PD)
equipped to accept low voltage power
transmitted over Ethernet cabling.