June 2005
Intermediate to advanced
502 pages
21h 48m
English
Content preview from Switching to VoIP
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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. ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.