Quick Guide to PoE (Power Over Ethernet)

May 5, 2006 by Garrett Smith

The RJ45 (CAT5) cabling that connects your office or home networking can be utilized for more than transporting voice or data across your local area network (LAN). The IEEE 802.3af Power over Ethernet standard was created as the standard method of delivering power to hardware devices such as IP Phones, IP Video Cameras and other network equipment. With PoE, there is no need to power some devices locally with an external AC power supply, they can simply receive their required voltage over the network cabling.

A POE system is comprised of three elements, the power sourcing equipment (PSE), the device which needs to be powered (PD) and the cable.

The Power Sourcing Equipment (PSE) is connected to a device, and determines if the device is IEEE 802.3af compliant or non-compliant. If determined to be a non-compliant device, no electrical current is passed through the network cable to the device. If the device is determined by the PSE to be a PoE compliant device, the required voltage is supplied to the device to power it.

There are several varieties of Power Sourcing Equipment to fit your specific requirements.

Power Sourcing Equipment (PSE)

Single Port (RJ45) PoE Injector – designed to provide PoE to a single device, a single PoE Injector has (2) RJ45 network connections. The network cable is plugged into the PoE Injector, where the necessary voltage is added. A second ethernet cable runs out of the PoE Injector and is connected to the device to be powered. Some examples of Single Port PoE Injectors include thePW130, and the Linksys WAPPOE”6

Mid-Span PoE Hub

Midspans come is port spans typically ranging from 4-24 ports. A Midspan PoE Hub does not have ethernet switching capability, it is designed to be paired in tandem with an existing ethernet switch, adding voltage for IEEE 802.3af compliant devices as needed. Midspans are a good choice for businesses that have existing 10/100 Ethernet switches already installed, and are less expensive than replacing legacy switches with newer, PoE enabled switches. The Midspan hub is typically stacked on the ethernet switch and each network cable is fed into the hub, where power is added, and then cabling run out to each specific network device. Some examples of Midspan hubs include the SEI Juicebox and a variety of products from PowerDsine.

PoE Switch

Many manufacturers offer ethernet switches with IEEE 802.3af PoE Midspan functionality built in. PoE Switches typically come in port span increments from 12-48 ports, and offer both 10/100/1000 Ethernet managed switching capabilities and PoE injection. Some examples of PoE Switches include the Linksys SRW224P and the Edgewater 2402

Benefits of Power Over Ethernet?

  • Easy, fast and convenient to install
  • Reduces overall power consumption
  • Reduces installation costs
  • Reduces cable runs
  • IEEE 802.3af is a unified, worldwide standard
  • It will save you money

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