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Date:      Thu, 27 Aug 2009 11:19:36 -0500
From:      "Midspan Manager" <Midspan@phihongusa.com>
To:        questions@freebsd.org
Subject:   Myths about Power Over Ethernet
Message-ID:  <20090827161939.49BBA1722@conqueror.xo.com>

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Myths about Power Over Ethernet
 August 27, 2009
Power-over-Ethernet (PoE) technology integrates power and data across =
standard Cat5/5e/6 network cabling and provides more flexibility in to=
day=E2=80=99s workplace. PoE enables power to be supplied to network d=
evices, such as IP phones, network cameras, and wireless access points=
 through a single, most often existing, network cable. When combined w=
ith an uninterruptable power supply (UPS) a PoE network delivers conti=
nuous operation and minimizes business downtime by eliminating most po=
wer interruptions. With the ability to install endpoints in any locati=
on PoE technology provides a scalable and flexible networking infrastr=
ucture geared for growth and efficiency.

=20
 PoE Switches can provide all the power I need or will need.
Today most switches are merely PoE-enabled.  This means the majority r=
ely on power management to share available power across the switch por=
ts. The switches are designed with a smaller power supply that is typi=
cally capable of powering the switch itself and providing the required=
 15.4 watts of power over a limited number of ports.=20
For example:  A 24-port PoE Switch with power management typically has=
 a 195-watt power supply. After the 40 watts needed to power the switc=
h, you have approximately 155 watts remaining. If 12 of the 24 ports a=
re used to connect end devices using 11.5 watts each, you would only h=
ave 17 watts remaining to provide power on the last 12 ports.  The mat=
h doesn=E2=80=99t match the ports: 195W =E2=80=93 40W (switch) =E2=80=93=
 138 (12 devices @ 11.5W/ea) =3D 17W left for power on 12 ports=20
Myth Busted: A PoE Switch is often not the best and most cost effectiv=
e solution.
=20
 =20
 A midspan and a PoE switch are the same.
A PoE Midspan is not a switch.  A Midspan is an additional PoE power s=
ource that can be used to offer full power to all endpoint devices.  P=
oE Midspans (Power Hub or Power Injector) pass data from a switch and =
=E2=80=98inject=E2=80=99 safe power acting as a patch panel of sorts. =
 Midspans are commonly used with either a non-PoE switch, an existing =
PoE switch, or a new PoE switch in a network. In addition to offering =
full power across all available ports, midspans costs substantially le=
ss per port and overall than a new PoE enabled switch.
Myth Busted: Midspans do not switch =E2=80=93 they make use of existin=
g best-in-class switches.  They inject safe power across all ports and=
 cost less than PoE switches. .=20
 =20
 Only a switch that has PoE built in should be used to power devices l=
ike IP Phones, Access Points, and IP Security Cameras.=20
Switches were designed to, well, switch.  PoE Switches are designed wi=
th power management and have to distribute different power as required=
 to ports but there is often not enough power for all devices plus the=
 power required to complete the primary task - switching.  Networks th=
at have multiple devices like IP phones, IP cameras, wireless access p=
oints quickly go beyond the limited capacity of managed power PoE swit=
ches.  As more PoE devices continue to grow in capabilities and market=
 share this managed power limitation will become more and more evident=
=2E  Midspans, in contrast to switches, were designed to provide full =
power on every port and deliver safe and reliable power based on the i=
ndustry standards (IEEE802.3af/at).=20
Myth Busted: Rather than relying on power management in a switch use a=
 midspan that can deliver full power (15.4W) to every port for all PoE=
-enabled devices now and in the future.  =20
 =20
 Ethernet devices not PoE-enabled (non 802.3af/at compliant) cannot be=
 powered using PoE technology.=20
Many devices do not directly accept Power-over-Ethernet but can still =
use PoE technology. If the device uses less than 12.5 watts (802.3af) =
or less than 50 watts (802.3at+) and connects to an IP Ethernet networ=
k you can use a PoE splitter.  PoE splitters enable you to accept PoE =
power from any IEEE 802.3af/at compliant switch or midspan then separa=
tes the data and power on to two seprate cables.  The data is connecte=
d to the end device through a standard RJ45 plug while the power is co=
nnected using a standard 5.5 x 2.1 x 12mm Adapter Plug.  Splitters can=
 also convert the input voltage to the required voltage for a non-PoE =
device. Splitters are traditionally used with older network products w=
hich only accept power through their (DC) jack and data through their =
RJ-45 jack.
Myth Busted: PoE splitters can be used in conjunction with PoE midspan=
s and switches to provide both the data connectivity and power require=
d by most endpoint devices.=20
 =20
 I need/will need additional PoE switch ports to power my IP cameras a=
nd high-power pan, tilt, and zoom (PTZ) cameras.=20
Today, many devices have evolved into more advanced solutions with hig=
her power requirements. The traditional approach was to endure a =E2=80=
=9Cforklift upgrade=E2=80=9D. This meant buying new PoE switches at co=
nsiderable cost and physically swapping out the existing switches to m=
eet higher power requirements or add more powered ports. There is an e=
asy and more cost-effective way =E2=80=93 separate the data and power =
in the wiring closet (IBF). It is more efficient and costs less to sep=
arate your data and power allowing you to keep your best-in-class busi=
ness switch for your IP needs and supplement it where required with be=
st-in-class midspan technology to power the endpoints.=20
Myth Busted: A PoE Switch is often not the best and most cost effectiv=
e solution.=20
 =20
 All midspans are created equal . . . they are all the same.=20
Always select a best-in-class midspan. If you wanted to enhance your s=
witched network wouldn=E2=80=99t use a best-in-class network switch?  =
Of course you would. A midspan designed and manufactured by a leading =
power supply company that understands power, power requirements, and o=
ne that delivers enterprise-level solutions.=20
Select a midspan manufacturer that has multiple members on the IEEE (P=
oE) committee helping to define safe, new PoE standards. This ensures =
that every midspan is designed to meet current and future IEEE specifi=
cations for Power-over-Ethernet.=20
Select a midspan manufacturer that designs, manufactures, and tests it=
s own product rather than outsourcing these tasks across the globe to =
cut costs.
Select a midspan that has a high-speed, common interface to access the=
 management console. A USB port is not as cheap as a serial port (RS-2=
32) but is faster, more user-friendly, and more common on high quality=
 midspans.=20
Myth Busted: Although there are many midspan manufacturers out there, =
few have the power supply experience, quality controls, and manufactur=
ing capability to produce best-in-class midspans.  All midspans are NO=
T created equal. =20
 =20
=20
=C2=A92009 midspans.com.
Midspans.com is a division of Phihong USA Inc. All Rights Reserved=20
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