Passes the invocation request to the appropriate
            callback.

def handle_invocation(self, message):
        """ Passes the invocation request to the appropriate
            callback.
        """
        req_id = message.request_id
        reg_id = message.registration_id
        if reg_id in self._registered_calls:
            handler = self._registered_calls[reg_id][REGISTERED_CALL_CALLBACK]
            invoke = WampInvokeWrapper(self,handler,message)
            invoke.start()
        else:
            error_uri = self.get_full_uri('error.unknown.uri')
            self.send_message(ERROR(
                request_code = WAMP_INVOCATION,
                request_id = req_id,
                details = {},
                error =error_uri
            ))