Switching to VoIP

This is the Title of the Book, eMatter Edition

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

Implementation Plan

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181

VPN

Virtual private networks have proven to be both a substantial cost saver and, some-

times, a substantial headache. They’re great because they allow the Internet to be

leveraged in a wide area connectivity application and allow remote offices and road

warriors to connect to the data center to check their email, update their database

apps, and synchronize their Palm Pilots. Most of the time, VPN is great for these

apps, because they are not sensitive to lag, jitter, and packet loss.

But VPN poses a much greater challenge to VoIP—for two reasons. First, VPN is

especially laggy and ridden with the overhead of tunneling and encryption. Second,

most VPN techniques don’t provide for any quality-of-service monitoring or enforce-

ment. So, like broadcast Ethernet or VoIP over dial-up, you may be able to use VPN

to carry voice calls, but the quality and consistency of those calls will be unpredict-

able. Chapter 13 includes a configuration for a Cisco router that enables a VoIP

trunk using a VPN tunnel.

Managed VPN

In response to the quality shortcomings of VPN, some carriers have begun to intro-

duce a service called managed VPN. This service connects multiple sites within your

organization to one another completely within a single carrier’s network rather than

the