def METHOD_NAME(self, req):
    payload = struct.pack("hh", req.a, req.b)
    self.response_received = None
    self.send_data(bytes(ApplicationPacket(37, payload)))
    start = rospy.Time.now()
    while self.response_received is None:
        if rospy.Time.now() - start > rospy.Duration(1):
            return -1
    res = ApplicationPacket.from_bytes(
        self.response_received,
        expected_identifier=37,
    )
    my_sum = struct.unpack("i", res.payload)
    return my_sum