Such coordination is surprisingly difficult if we are not careful. There are many protocols for implementing the agreements. Most of the distributed systems we actually use fall into the latter category. 33 Coordination and agreementConsens and related problems Conclude an agreement in a distributed manner Reciprocal exclusion: Who can enter the critical region Multicast completely ordered: the order of communication Byzantine Generals: attack or withdrawal? Consensus (agree) Problem Agree on a value after one or more of the processes have suggested what the value should be failure of the coordinator is more difficult….