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Introduction
This chapter provides an overview of Power over Ethernet (PoE) and a list of reasons why a user might want to implement PoE in their environment. It discusses how PoE transmits power over twisted pair cable and the capabili ties of the devices used to provide PoE.
Overview
Power over Ethernet technology allows IP telephones, wireless LAN Access Points and other appliances to receive power as well as data over existing LAN cabling, without needing to modify the existing Ethernet infrastructure.
IEEE 802.3af is an extension to the existing Ethernet standards. Power Over Ethernet is likely to become a standard feature of ethernet switches in a few years, as the cost of adding power supplies to the Ethernet switches is going to be small. It offers the first truly international standard for power distribu tion (consider how many different AC power plugs exist worldwide).
Almost all appliances require both data connectivity and a power supply. Just as telephones are powered from the telephone exchange through the same twisted pair that carries the voice, we can now do the same thing with Ethernet devices.
The technology is bound to make a big impact in the world of embedded computing. In the realm of embedded computers, where the systems are increasingly connected to LANs and the internet, the advantages of providing power and data through a single cable should be obvious. Consider a typical application: a system for a car park that includes security cameras, informa tion signs,
Introduction