Total Order Broadcast

Total-order broadcast makes every participant in a distributed system deliver the same messages in the same order. Invalid operations must be rejected consistently without changing state.

It is closely related to consensus: repeated agreement on the next message can build an ordered broadcast log.

For example, if a server has delivered messages 1 through 3 and receives message 5, it waits for message 4 before delivering 5. Otherwise different servers could deliver 4 and 5 in different orders.