Use TT_REQUEST
for messages that return values or status. You will be informed when the message
is handled or queued, or when a process is started to handle the request.
Use TT_NOTICE
for
messages that only notify other processes of events.
Use TT_OFFER
for
messages for which there are multiple intended recipients, and for which you
wish to determine how many of those recipients have accepted, rejected, or
abstained from participation in this message.