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List:       freebsd-doc
Subject:    Myths about Power Over Ethernet
From:       "Midspan Manager" <Midspan () phihongusa ! com>
Date:       2009-08-25 0:30:49
Message-ID: 20090825003056.6DE97796C () warrior ! xo ! com
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Myths about Power Over Ethernet
 August 24,2009
Power-over-Ethernet (PoE) technology integrates power and data across standard \
Cat5/5e/6 network cabling and provides more flexibility in today's workplace. PoE \
enables power to be supplied to network devices, such as IP phones, network cameras, \
and wireless access points through a single, most often existing, network cable. When \
combined with an uninterruptable power supply (UPS) a PoE network delivers continuous \
operation and minimizes business downtime by eliminating most power interruptions. \
With the ability to install endpoints in any location PoE technology provides a \
scalable and flexible networking infrastructure geared for growth and efficiency.

 
 PoE Switches can provide all the power I need or will need.
Today most switches are merely PoE-enabled.  This means the majority rely on power \
management to share available power across the switch ports. The switches are \
designed with a smaller power supply that is typically capable of powering the switch \
itself and providing the required 15.4 watts of power over a limited number of ports. \
 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 switch, you have approximately \
155 watts remaining. If 12 of the 24 ports are used to connect end devices using 11.5 \
watts each, you would only have 17 watts remaining to provide power on the last 12 \
ports.  The math doesn't match the ports: 195W – 40W (switch) – 138 (12 devices @ \
11.5W/ea) = 17W left for power on 12 ports  Myth Busted: A PoE Switch is often not \
the best and most cost effective solution.  
  
 A midspan and a PoE switch are the same.
A PoE Midspan is not a switch.  A Midspan is an additional PoE power source that can \
be used to offer full power to all endpoint devices.  PoE Midspans (Power Hub or \
Power Injector) pass data from a switch and ‘inject' 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 less per port and overall \
than a new PoE enabled switch. Myth Busted: Midspans do not switch – they make use \
of existing best-in-class switches.  They inject safe power across all ports and cost \
less than PoE switches. .   
 Only a switch that has PoE built in should be used to power devices like IP Phones, \
Access Points, and IP Security Cameras.  Switches were designed to, well, switch.  \
PoE Switches are designed with 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 that have \
multiple devices like IP phones, IP cameras, wireless access points quickly go beyond \
the limited capacity of managed power PoE switches.  As more PoE devices continue to \
grow in capabilities and market share this managed power limitation will become more \
and more evident.  Midspans, in contrast to switches, were designed to provide full \
power on every port and deliver safe and reliable power based on the industry \
standards (IEEE802.3af/at).  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.     
 Ethernet devices not PoE-enabled (non 802.3af/at compliant) cannot be powered using \
PoE technology.  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 network 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 separates the data and power on to two seprate \
cables.  The data is connected to the end device through a standard RJ45 plug while \
the power is connected 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 which 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 midspans and switches to provide both the data \
connectivity and power required by most endpoint devices.   
 I need/will need additional PoE switch ports to power my IP cameras and high-power \
pan, tilt, and zoom (PTZ) cameras.  Today, many devices have evolved into more \
advanced solutions with higher power requirements. The traditional approach was to \
endure a "forklift upgrade". This meant buying new PoE switches at considerable cost \
and physically swapping out the existing switches to meet higher power requirements \
or add more powered ports. There is an easy and more cost-effective way – separate \
the data and power in the wiring closet (IBF). It is more efficient and costs less to \
separate your data and power allowing you to keep your best-in-class business switch \
for your IP needs and supplement it where required with best-in-class midspan \
technology to power the endpoints.  Myth Busted: A PoE Switch is often not the best \
and most cost effective solution.   
 All midspans are created equal . . . they are all the same. 
Always select a best-in-class midspan. If you wanted to enhance your switched network \
wouldn't 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 one that delivers enterprise-level solutions.  Select a midspan \
manufacturer that has multiple members on the IEEE (PoE) committee helping to define \
safe, new PoE standards. This ensures that every midspan is designed to meet current \
and future IEEE specifications for Power-over-Ethernet.  Select a midspan \
manufacturer that designs, manufactures, and tests its 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-232) but is faster, more user-friendly, and more common on \
high quality midspans.  Myth Busted: Although there are many midspan manufacturers \
out there, few have the power supply experience, quality controls, and manufacturing \
capability to produce best-in-class midspans.  All midspans are NOT created equal.    \
  
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Midspans.com is a division of Phihong USA Inc. All Rights Reserved 
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