Switching to VoIP

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

Network Environment

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177

PoE is often just called inline power.

Consider the power requirements of your IP phone fleet. Will they work with 802.

3af, or do they require a proprietary power standard? Do the switches in place today

provide the right kind of power, or any at all? Is connecting an AC/DC adapter at

each phone location a reasonable idea? It may be in a 5-person office, but all those

adapters could really add up in a 500-person office. How does the addition of switch-

delivered power affect your VoIP rollout cost estimate?

Provisioning a central power source with PoE simplifies the task of supplying backup

power. Three or four PoE switches in a single rack are much easier to connect to a

UPS or backup generator than a building full of IP phones in separate offices.

Power injection

A number of vendors offer patch panels that inject inline power. Avaya and others

offer 802.3af injectors that allow you to add PoE to your network without forklifting

all of your non-PoE switches. Sometimes, PoE injectors are a less expensive proposi-

tion than PoE switches, especially when the switches themselves are young, can’t be

easily replaced, or are leased for a long term. That said, green field rollouts will likely

want to avoid power injectors, because they take twice as much rack space