VoIP sniffer

Hi all,
Sorry if this is not the right place to ask for.
I am planning to write a VoIP sniffer using Digium Wildcard TE110P, not only for Asterisk, but also for another PBXs.
Anybody knows any document, or an idea where to start from.
Thanks for your help.

If you need to sniff voip calls, you can use WinPCap SDK(winpcap.org/).

  1. Start listening the ethernet traffic
  2. Analyse every UDP packet, does it conform to RTP packet format.
  3. If yes, decode voice to regular PCM format and store on disk.

Note, that for decoding the voice, you need to implement decoders (for example, G.711, G.729, G.723.1, GSM etc).

Here is a link to commercial application that does above things