Typically, I learned in lecture that Totally Ordered multicast with Lamport clocks can be achieved under assumption that network is reliable and FIFO multicast order.
This requires total message of N (initial broadcast) + N^2 (ACKs)
However, one of the question I had was optimize the above algorithm so that it has same total ordering but incur significant fewer total messages. Also, it should also work under reliable network, but without FIFO.
Can we actually achieve optimized algorithm (reduce number of messages) without FIFO guarantee in network?