[Users] Active sessions - dialog

Hello I need to write a CAC (Call Admission Control) module for an 802.11 AP (Access Point). The idea is to use a SIP Proxy to monitoring bandwith utilization according to codec, and allow or disallow new sessions, depending on resources. On a first stage I just want to limit the session to a fix number. For that, for each new session request (INVITE), I need to know how many active session there is already. I think using the module dialog but it is experimental. What is exactly its status? Is it usable for now? Is there another way to get information about the number of active sessions? Thanks. Regards, Michel