This paper is a Systematization of Knowledge (SoK) on Directed Acyclic Graph (DAG)-based consensus protocols, analyzing their performance and trade-offs within the framework of consistency, availability, and partition tolerance inspired by the CAP theorem.

We classify DAG-based consensus protocols into availabilityfocused and consistency-focused categories, exploring their design principles, core functionalities, and associated trade-offs. Furthermore, we examine key properties, attack vectors, and recent developments, providing insights into security, scalability, and fairness challenges. Finally, we identify research gaps and outline directions for advancing DAG-based consensus mechanisms.

1 The Avalanche crypto project is no longer pursuing the case of UTXOs and their Avalanche consensus protocol on its main net and currently uses an account-based ledger state with a consensus protocol named Snowman.