FMS XMPP Integration

I have to build up a solution where patients, doctors and other staffer members can comunication with each other either through video, audio or through messages.

I know how to communicate through video or audio using fms. But i am not clear how it integrates with an xmpp server.

It is possible to manage user list, his status and call establishment through FMS using remote method invocation but why there is common practice to use xmpp server for that?

If we use xmpp server and fms, will user connects in both xmpp server and fms or when user tries a video / audio call?

Which part is handled by which server? e.g list managment, chatting, call establishment ?

I don't know in detail about the xmpp server but  i know that it is a common practice to use this server for bulding messenger service. 

If any one knows about any googd article on fms and xmpp integration that will be very helpfull.