@staticmethod
def _subscribe_broadcast(sub_id, channel, callback, **kwargs):
    """Listen to a broadcast topic, notify via callback function.
        :param sub_id: ID for this subscription in the transport layer
        :param channel: Topic name to subscribe to
        :param callback: Function to be called when messages are received
        :param **kwargs: Further parameters for the transport layer. For example
               retroactive: Ask broker to send old messages if possible
        """
    raise NotImplementedError('Transport interface not implemented')
