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Power Over Ethernet Buying Guide

Power over Ethernet is a powerful group of technologies that simplifies the installation of IP Phone Systems, while increasing flexibility and reliability.

By sending both data and power through the Ethernet cable, PoE reduces installation type because there is no need for an external power supply. Moves and adds are streamlined because only one cable is needed to get the phone up and running. PoE unclutters the workspace by removing yet another cable to get twisted and tangled behind a workstation.

PoE also increases flexibility because you can install devices away from the power grid. If need an IP phone or IP camera in a distant part of the warehouse, PoE can allow you to install in locations away from power outlets.

PoE increases reliability because you remove one point of failure, the external power supply. External power supplies can fail, get crushed by chair leg or accidentally get unplugged. Another advantage of PoE is the ability to have central battery backup. If you install a battery backup system (UPS) on the PoE Switch, all of the IP phones will maintain power in the event of a power failure.

Types of PoE Hardware:
PoE Switches - Networking switches that generally have 4 to 48 RJ45 Ethernet ports that transmit both data and power through the Ethernet cables connected to it. Some PoE switches only have half of their RJ45 ports powered by PoE. The NETGEAR FS726TP for example has 24 total ports but only 12 are powered with PoE. On the smaller end of PoE switches you can also find solid state devices. These fanless PoE switches are much quieter than a switch with a fan. The NETGEAR FS116P for example has 16 ports (8 PoE) and has no moving parts.

PoE Injectors – Devices that inject power into the data cable and then feeds power to the device. If you only need to power 1 or 2 devices PoE injectors can be a cheaper option than a full PoE switch. The AASTRA-POE-INJECTOR for example is perfect if you just need to power one phone at the back of the warehouse.

PoE Splitters – are devices that split the power from the data on the device end. So if you have a phone that does not support PoE, take the Linksys SPA921 IP phone example. You can use a splitter to separate the power from the Ethernet cable and the phone is none the wiser. For example the Linksys POES5 will receive the PoE and then split into a power insert and an RJ45 insert to plug in the phone.

What is the 802.3af Standard? (a term coined by engineers to intentionally make PoE confusing =)
802.3af is a standard, an agreed upon way of manufacturing equipment so they all work together. Many manufacturers produce PoE equipment, if they don't agree on certain specifics, the equipment will not interoperate.

Although there are several standards of PoE, 802.3af is by far the most popular in use today. If your IP phone supports 802.3af and your PoE switch supports 802.3af, then the switch will power the phone properly. Cisco also had a PoE standard that has been discontinued in favor or 802.3af which is why all of the newer Cisco phones (CP-7941G, CP-7961G, CP-7970G and newer) support the 802.3af standard.

Is PoE more expensive than just buying power supplies?
It depends on how many phones you are installing from what manufacturer. If you are installing 5 Grandstream IP Phones, PoE is going to be more expensive. But PoE can also be cheaper when compared to using external power supplies in the right situation. Using the Cisco 7941G as an example, the power supply (CP-PWR-CUBE-3) cost $40.00. If you deploy 20 phones you would spend $800.00 in power supplies. The Linksys SRW224P 24 port PoE Switch costs around $450.00, saving you $350.00 in installation cost & decreasing cable clutter and installation time to boot. This generally only applies to installation of 15 or more Cisco phones. Other manufacturers power supplies are cheaper, usually around $20.00 and if you are only installing 5 phones, PoE will end up costing you more not matter what manufacturer you use.