There are several packet capture and trace tools for OpenSER. One of the simplest is ngrep used throughout this book. TShark, former Tethereal, is a nice tool if you have a server without a GUI. With Tshark you can export the captured packets to analyze on Wireshark. Trace tools such as the SIPTRACE module are cool too. However they can impact the performance of your system when enabled. The SIPTRACE module logs the inbound and outbound traffic passing through the proxy for a marked transaction to a database.
Wireshark (former Ethereal) is the most used protocol analyzer available in the market and it is GPL licensed. Usually you don't have a GUI (graphical user interface) in your server, but you can still capture the packets using the text version of Wireshark known as TShark. We often use ngrep, because it is very simple and light. To teach you exactly how to use a protocol analyzer is beyond the scope of this material; however, we will...