PoE Networks

Oct. 20, 2005

What is the basis for Power over Ethernet (PoE)?

The IEEE 802.3af standard for PoE enables data terminal equipment (DTE) to receive power over the same cabling used for data in an Ethernet network. The standard specifies the protocol for delivery of a nominal 48 V dc over unshielded twisted-pair cables (such as CAT-5). This eliminates the need for a local power source.

What does IEEE802.3af cover?

The IEEE 802.3af standard presents the requirements for providing and receiving power over the existing Ethernet cabling. It involves power-sourcing equipment (PSE) that provides the power on the cable for the powered device (PD). The figure shows a simplified version of a typical PoE system.

What are some typical PDs employed in PoE?

PDs include VoIP phones, security systems, and point-of-sale terminals.

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About the Author

Sam Davis 2

Sam Davis was the editor-in-chief of Power Electronics Technology magazine and website that is now part of Electronic Design. He has 18 years experience in electronic engineering design and management, six years in public relations and 25 years as a trade press editor. He holds a BSEE from Case-Western Reserve University, and did graduate work at the same school and UCLA. Sam was the editor for PCIM, the predecessor to Power Electronics Technology, from 1984 to 2004. His engineering experience includes circuit and system design for Litton Systems, Bunker-Ramo, Rocketdyne, and Clevite Corporation. Design tasks included analog circuits, display systems, power supplies, underwater ordnance systems, and test systems. He also served as a program manager for a Litton Systems Navy program.

Sam is the author of Computer Data Displays, a book published by Prentice-Hall in the U.S. and Japan in 1969. He also authored the book Managing Electric Vehicle Power. He is also a recipient of the Jesse Neal Award for trade press editorial excellence, and has one patent for naval ship construction that simplifies electronic system integration.

You can also check out additional articles on his other author page.