How can I be sure that UDP messages are received in order?
You can't. What you can do is make sure that messages are processed
in order by using a numbering system as mentioned in ``5.5 How can I
be sure that a UDP message is received?''. If you need your messages
to be received and be received in order you should really consider
switching to TCP. It is unlikely that you will be able to do a better
job implementing this sort of protocol than the TCP people already
have, without a significant investment of time.