def METHOD_NAME(self, packet, other_address, transmit_callback=None):
    """Called by SCHC when a (SCHC) packet is to be sent on the LPWAN.
    :param packet: The SCHC packet, SCHC fragment or SCHC ACK, to be sent
    :param other_address: The (MAC) address of the other side
    :param transmit_callback: A function called after completion of the 
        transmission, with a transmission status (XXX: defined?)
    """
    abstract