This is my first project I did with the resiprocate SIP stack. There's a lot of things left to do in this project but I wanted to post the code here right away in case someone needs more example on how to use resiprocate.
Dependencies and limitations
I chose to use resiprocate as the SIP stack and ortp as the RTP stack and libxml2 and the XML parser. The application only supports G.711 uLaw. The application only supports SIP info for receiving DTMF (inband and RFC2833 not supported).
Resiprocate
Resiprocate provides a Dialog Usage Manager (DUM). This engine is very useful for applications that don't want to deal with low level SIP messages. The DUM allows you to receive events such as onOffered, onAnswer, onTerminated (plus many more) by the use of an observer pattern. Using a class called AppDialogSet, it is possible to represent a "call" or a "dialog" and let the DUM manage it. For example, you could override the AppDialogSetFactory with your own CallFactory that would create "Call" objects derived from AppDialogSet. When receiving an event such as onOffered, the DUM will already have created a AppDialogSet with your factory class and you can then cast this AppDialogSet with your "Call". This is a good way to receive a "Call" reference on every events you get. And the beauty of this is that you never need to delete it becausr the DUM will take care of it. More information is available on the resiprocate website.
ortp
ortp is very easy to use but only provides basic functionalities. It won't bind to any sound cards or include encoding like other fancy stack do. This stack only allows you to open a stream and feed it data encoded with whatever codec you want. It is the developper's responsibility to make sure that the data that is fed is encoded with the proper codec.
Threading model
I chose to use 1 thread for general processing and 1 thread for each RTP session. The main thread is used to give cycles to the resiprocate DUM and to the WakeupCallService. A new thread is created for each RTP sessions. The RTP session only handles outgoing stream since we don't need the incomming stream. The ortp stack provides a way to read multiple streams from the same thread but I prefer to use different threads in order to leverage multi-cores CPUs.
Usage
The server is a user agent that registers with you PBX. Just call the server and enter the time at wich you want your wakeup call and the extension at which you wanna be notified. For example, you would enter 0,6,3,0 to get a wakeup call at 6h30 AM. I left out the prompts from the package so you'll want to replace them. The IVR is defined in the xml file. Just change the prompt names. There is no configuration file you can use right now. You will need to set the proper values that you need in config.h. To launch the application, run it and provide, as a command line argument, the ip address on which to bind on your computer.