HP ProCurve 1600M Manuale di pianificazione e attuazione - Pagina 7

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.

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, call-for-help telephones and vehicle sensors. Such a system is

distributed over a significant area, where main power is not easily available.

A single link to a PoE Ethernet Switch makes implementing this system less

expensive and faster than using a non-PoE switch.

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