Switching to VoIP

This is the Title of the Book, eMatter Edition

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

SIP Packet Inspection

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• A packet sniffer such as Ethereal, which runs on several platforms. It’s available

at http://www.ethereal.com. Snort can be useful for troubleshooting security

issues, too.

• If you’re troubleshooting from behind a firewall, you’ll need access to an unfire-

walled public IP address, too. SIP can be stymied by NAT firewalls (more on this

later).

• A SIP server like SIP Express Router (http://www.iptel.org/ser) or a SIP-compatible

registrar like Asterisk or VOCAL. In this book, we’ve used Asterisk. For H.323 set-

ups, a free gatekeeper and gateway like those included in Open H.323 are

recommended.

The Three Things You’ll Troubleshoot

Latency

On the Internet, the round-trip latency of a phone call can be relatively stable

from one moment to the next but vary heavily from one day to the next. You’ll

use troubleshooting tools to find the sources of latency that can make VoIP call

quality fluctuate.

Jitter

On the Internet, moment-to-moment changes in latency are called jitter. Jitter is

a huge problem. You’ll use troubleshooting tools in order to identify the root

causes of jitter.

Signaling and interoperability problems

Perhaps the most difficult to isolate, interoperability problems require a work-

ing knowledge of the signaling protocols you use on your VoIP network. ...