6.1. Hacks 7287: Introduction
Switching to Voice over IPespecially in an enterprise environmentis wrought with perils that you won't experience on a non-VoIP network. Real-time applications like voice require a high-quality, real-time network. And, at least by itself, traditional Internet Protocol (IP) networking gear doesn't fully deliver on that promise. Fortunately, you can apply some old toolssuch as Perl and Etherealto VoIP networking to troubleshoot and improve your IP network.
When problems occur, your trusty old network troubleshooting apps will come to the rescue. In this chapter, you'll use Ethereal to sniff Session Initiation Protocol (SIP) signaling messages as they traverse the network inside of User Datagram Protocol (UDP) packets. If you're a seasoned hacker or a timid script kiddie, you can start with this chapter's Perl scripts, which graph and monitor VoIP activity on the network. You'll also be able to monitor latency and jitterthe two things VoIP admins want to avoid like the plagueusing standard IP networking commands.
If you play your cards right, you might even learn how to beat a SIP-mangling firewall. (OK, you don't have to play cards at all. Just read "Explore NAT Traversal" [Hack #76].) I'll also show you how to clandestinely monitor and record actual VoIP phone callsthe IP equivalent of a phone tap.