Date: Thu, 7 May 2009 11:21:51 -0500 From: "Midspan Manager" <Midspan@phihongusa.com> To: doc@freebsd.org Subject: Myths about Power Over Ethernet Message-ID: <20090507162151.D4CBA782D@thunderer.xo.com>
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Myths about Power Over Ethernet May 7, 2008 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 You are being sent this email because you have expressed interest in = PoE products in the past. If you do not wish to receive emails from us= in the future and be removed from our list please click on the link b= elow.=20 To unsubscribe, please click here. www.phihong.com - 47800 Fremont Blvd., Fremont, CA. 94538 - Phone 510-= 445-0100=20
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