* MAX_RTT - this is the maximum time it should take for a sent message to arrive at all parties. If you send a message and haven't received it back within MAX_RTT, something is wrong.
* MAX_RTD - this is the maximum difference in time when a message arrives at all parties. If you receive a message whose parent was received before that's not a successor of a message (X) you received more than MAX_RTD + MAX_RTT time ago, something is wrong. (This is because message X might have arrived at the other party more than MAX_RTD after you saw it, and the other party's message might have taken MAX_RTT to reach you. But after MAX_RTD + MAX_RTT, there's no excuse for the other party not to have seen X).
* MAX_CONFIRM - this is the maximum time an existing member may spend after receiving a new user's JOIN message before sending a CONFIRM message in response. If the new user hasn't received CONFIRM messages from existing membership within 2*MAX_RTT + MAX_CONFIRM, something is wrong.