There is interesting article about Voice over IP (VoIP) Sniffer and Call Detector at: https://www.enderunix.org/voipong/
It is stated there that VoIPong is a utility which detects all Voice Over IP calls on a pipeline, and for those which are G711 encoded, dumps actual conversation to seperate wave files. It supports SIP, H323, Cisco’s Skinny Client Protocol, RTP and RTCP.
Quote from site:
It’s been written in C language for performance reasons, proved to be running on Solaris, Linux and FreeBSD; though it’s thought to compile and run on other platforms as well.
On a 45 Mbit/sec actual network traffic, it’s been verified that VoIPong successfully detected all VoIP gateways and the VoIP calls. CPU utilization during the run has been found ranging between 66% – 80% on a 256MB RAM, Celeron 1700 Mhz Toshiba notebook.
Produces real .Wav files for direct audio hearing.
Simple, optimized, extandable fast code
The algorithm doesn’t depend on signalling but on RTP/RTCP
Detailed logging. (Comfortable for ‘cut’ and ‘cat’ operations to produce statistics.)
Powerful management console interface
Easy installation and administration
Note: Thanks to Robert B. who pointed me to this tool.