def reserve_ids(self, resource, num_ids):
        """Reserve a block of unique, sequential ids for annotations.

        Args:
            resource (intern.resource.Resource): Resource should be an annotation channel.
            num_ids (int): Number of ids to reserve.

        Returns:
            (int): First id reserved.

        """
        return self.service.reserve_ids(
            resource, num_ids,
            self.url_prefix, self.auth, self.session, self.session_send_opts)