When troubleshooting many types of network problems, a protocol analyzer is an invaluable tool. However, for VoIP and IP Telephony, it's often overlooked, as many organizations don't want to spend the money to get a tool that can decode and play back audio from a capture file. But, you may have tools you don't know about.
If you're using Cisco's Unity voice mail server, there are two spiffy utilities tucked inside. As with all the good stuff, Cisco recommends you only use these with TAC assistance. Yeah, whatever...
The first tool is called "capripper." Every protocol analyzer I'm aware of allows you to store captured packets in a .cap format. You can capture various VoIP conversations with the analyzer of your choice, and then feed the .cap files to capripper, which, among other things, will save each RTP conversation it finds in a separate .wav file.
This is really handy for a lot of reasons. First, even if you have a top-shelf protocol analyzer like
Second, capripper makes it much easier to archive the files. You can use this to baseline the network, and compare audio. Storing the RTP streams separately means you can give each a filename, etc.
The second tool that comes with Unity is called "RTP Parser". It's an add-on to Microsoft's NetMon, the packet-capturing and protocol-analyzing utility that is built-in to all the Windows server products since the first NT version. For details on RTP Parser, and on capripper, visit Cisco's website and read up on both of these two freebies.
Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.
This was first published in December 2003