'Process the session_start event.
Typical actions for the session_start event are
requesting the roster and broadcasting an initial
presence stanza.
Arguments:
event -- An empty dictionary. The session_start
event does not provide any additional
data.'

def start(self, event):

    self.get_roster()
    self.send_presence()
    self.plugin['xep_0045'].joinMUC(self.room, self.nick, wait=True)
