'Registered' message mode is
generally used for games that do not require messages to be sent
quickly (less than half a second) e.g. card games, turn based
games etc.
In this mode, TNT Basic confirms
that a message arrived and it is resent if necessary. This means
that it is a lot slower but it is more reliable.
To switch to 'Normal' mode,
use the command Set Networking
Normal.