The hierarchical daisy architecture for causal delivery

In this paper, we propose the hierarchical daisy architecture, which provides causal delivery of messages sent to any subset of processes. The architecture provides fault tolerance and maintains the amount of control information within a reasonable size. It divides processes into logical groups. Messages inside a logical group are sent directly, while messages that need to cross logical groups' boundaries are forwarded by servers. We prove the correctness of the daisy architecture, discuss possible optimizations, and present simulation results.