[Serusers] How to make SER keep states

Hi, I'm working with SER and I'm trying to make a state machine for SER. I'm having some difficults on trying to understand how modules work, because SER have to be extended to enable such functionality. The idea is to SER recognize that a client has already estabilished a conection with a video server throught SER's proxy and therefore SER must redirect the new INVITE to another proxy. In this new proxy the trafic will be multicast, so that everyone who wants the same video service will have it. SER just need to recognize that two or more clients wants to estabilish conection with the same terminal. Can you help me in how or where in the modular arquitecture of SER will I have to act? Thanks.