how fms manage netGroup?

i just not understand how fms manage netGroup? i try to find in multicast application but none,its just republish use rtmfp, any one can tell me how do that?

  when client do

nc = new NetConnection();

nc.addEventListener(NetStatusEvent.NET_STATUS,onNetStatus);

nc.conncet('rtmfp://192.168.1.10/multicast');

nc.client = this;

protected function onNetStatus(event:NetStatusEvent):void

{

     trace(event.info.code);

     switch(event.info.code)

     {

          case 'NetConnection.Connect.Success':

                ns= new NetStream(nc,groupSpec);

                ns.addEventListener(NetStatusEvent.NET_STATUS,onNetStatus);

                break;

          case 'NetStream.Connect.Success':

                 ns.attachCamera(Camera.getCamera());

                 ns.publish('p2pstream');

     }

}

so ,when netStream publish stream ,how server side do, how server get groupSpec? how when other peer

connect the same group, sever join that peer to group?