Consensus: Power and Implementability Limit in Crash-Prone Asynchronous Systems

Abstract

This chapter first presents the TO-broadcast communication abstraction, the state machine replication paradigm, and the ledger object, and shows that they all are computationally equivalent. It also shows that any object (abstraction) defined by a sequential specification (sequential state machine, or ledger) can be implemented in CAMP_n,t[CONS] (CAMP_n,t$[\emptyset]$ enriched with consensus). In this sense the consensus agreement abstraction is universal. It provides the computability power needed to implement any object – defined by a sequential specification – despite asynchrony and the crash of any minority of processes.