One of the most valuable aspects of a VoIP provider is billing. Let's examine an open-source tool called CDRTool to do this. CDRTool has been developed by AG Project (www.ag-projects.com) and is licensed according to GPL.
CDRTool is a web application able to rate calls accounted in the FreeRADIUS tables. It is able to rate calls based in its internal tables. Beyond rating calls, the system is able to trace calls using the siptrace feature of OpenSER and apply anti-fraud mechanisms based on quotas. The component rating engine is a daemon that can receive TCP requests, making possible the implementation of a pre-paid mechanism.
In this material we will focus just on rating calls. Tracing calls will be seen in Chapter 11.