def _fetch(self):
        """
        Internal helper that fetches the ring from Redis, including only active
        nodes/replicas. Returns a list of tuples (start, replica) (see
        _fetch_all docs for more details).
        """
        now = time.time()
        expiry_time = now - NODE_TIMEOUT

        data = self.conn.zrangebyscore(self.key, expiry_time, 'INF')

        ring = []

        for node_data in data:
            start, replica = node_data.decode().split(':', 1)
            ring.append((int(start), replica))

        ring = sorted(ring, key=operator.itemgetter(0))

        return ring