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detektor security
academy
behaviours of those network con-
nections and associated network
equipment.
EtherWAN, for example, has
over ten years of PoE Ethernet
switches design experience, and
in the quality assurance lab every
PSE needs to pass the PSE Con-
formance Test Suite offered by
Sifos Technologies. The test suite
for 802.3at produces up to 115
test parameters depending upon
PSE capabilities. These parameters
are measured in 23 distinct tests
that cover over 95 percent of the
PSE PICS (conformance check
list items) in the IEEE 802.3at
specification. The test is widely
used throughout the network-
ing community as the industry
"norm" for PSE specification
compliance.
Due to the fast pace of this sec-
tor, with most equipment having
a realistic lifespan of around five
years, it is most important to buy
a fully qualified system. If you buy
equipment which is not fully con-
formant to IEEE 802.3at or IEEE
802.3af, you might end up having
to deal with a real nightmare in
the future. n
PoE challenges design and test
engineers a great deal. Evaluating
the quality of a PSE comes down
to having to work with "smart"
multi-channel DC power sources
that are activated and deactivated
through signalling protocols oper-
ating over several power delivery
and polarity configurations. The
application and management of
DC power over multiple local
area network connections must be
completely transparent, safe, non-
destructive, and non-disruptive to
the traditional data transmission
PD networking devices can then
receive battery-backed power even
in power outages.
Centrally managed power
also enables remote shutdown or
remote reset capabilities. Through
managing a PoE-enabled LAN
switch via a web browser or by
SNMP, remote networking devices
can be easily reset or shut down
saving the time and expense of
dispatching a technician.
PSe Conformance Test
is important
Despite the various require-
ments described for PD detection
signaling in the 802.3 specifica-
tion, there is considerable room
for design variation. In practice,
detection pulses and detection
measurement schemes do vary
significantly across PSE interface
technologies. The 802.3at speci-
fication leaves considerable room
for implementation dependent
behaviours. Additionally, many
vendors of PSE will choose to go
outside the 802.3 specification in
ways that will affect the ability to
power and maintain pure 802.3at
PDs. This high degree of variation
adds a number of PoE compatibil-
ity issues, such as problems with
voltage levels.
power signaling mechanism that
constantly monitors for a 802.3
powered device (PD) to appear
at the end of the LAN cable. If a
non-powered network device is
connected, the PSE can function
just as a non-PoE and perform an
"ordinary" link to the networked
device. However, if an 802.3 PD
is connected, the PSE will quickly
recognise this and begin the pro-
cess of powering it up.
Cables
The IEEE standard for PoE re-
quires Category 5 cable or higher
for high power levels, but can
operate with Category 3 cable for
low power levels. But still, even
high quality outdoor Category 5
cable is much cheaper than USB
repeaters or AC wire.
Fault protection
To minimize the possibility of
damage to equipment in the event
of a malfunction, the more sophis-
ticated PoE systems employ fault
protection. This feature is good to
have and shuts off the power sup-
ply if excessive current or a short
circuit is detected.
UPS
PoE can increase your security
level through a so called central
UPS (Uninterrupted Power Sup-
ply) in the monitor room or cen-
tral control room where the PoE
Ethernet switch is located.
In case of a power outage,
critical networking devices will
become inoperable unless they are
protected by a UPS with battery
backup. Having the networked
equipment distributed throughout
your building or campus requires
the distribution of several UPS
systems. With PoE, a single, cen-
trally managed UPS can be used to
supply backup power to your PSE
equipment. All the distributed
Sponsored by
SECURITY ACADEMY
Effective IP surveillance
with Power over Ethernet
A few of the advantages with PoE
· Equipment can be placed in the most optimal location instead of choosing
one where power is available.
· Network installations can be accomplished cheaper, easier and faster.
· Network changes, such as adding, removing or moving something, can be
made much easier.
· Using a PoE infrastructure enables centralised power management capa-
bilities for critical network devices.
· PoE can be used in security applications where USB or AC power is unsuit-
able, inconvenient or too expensive to use.
Word list
·
ethernet Ethernet is a family of computer networking technologies for
local area networks (LANs) commercially introduced in 1980. Standardised
in the IEEE.
· Cat 5 Category 5 cable (Cat 5) is a twisted pair cable for carrying signals.
This type of cable is used in structured cabling for computer networks such
as Ethernet. It is also used to carry other signals such as telephony and
video. This category guarantees speeds of up to 100 megabit per second.
· IEEE The Institute of Electrical and Electronics Engineers is the world's
largest professional association dedicated to advancing technological in-
novation and excellence.
· UPS An uninterruptible power supply is an electrical apparatus that pro-
vides emergency power to a load when the input power source, typically
mains power, fails.
· Phantom power A technique used to allow the powered pairs in an
Ehternet cable to also carry data.
· Injector An injector is used to power PoE devices on a standard Ethernet
line that is not PoE.
About the sponsor
EtherWAN Systems, founded in 1996 with the US headquarters in Cali-
fornia and the Pacific Rim headquarters in Taiwan, has become a leader in
Ethernet connectivity for applications in various markets including IP surveil-
lance, intelligent transportation systems (ITS), electric utility, oil and mining,
factory automation, etc. EtherWAN specialises in designing and manufactur-
ing fiber optic Ethernet products and Ethernet equipment made especially for
harsh environments. Technical engineers are available for network topology
consultancy.
For more information about EtherWAN's solutions, visit: www.etherwan.com
Contact info: info@etherwan.com.tw
In EtherWAN's quality assurance lab every PSE needs to pass the PSE
Conformance Test Suite offered by Sifos Technologies.