A consistent history link connectivity protocol

The RAIN (Reliable Array of Independent Nodes) project at Caltech is focusing on creating reliable distributed systems by leveraging commercially available personal computers and interconnect technologies. Fault-tolerance is introduced into the communication infrastructure by using multiple network interfaces per compute node. When using multiple network connections per compute node, the question of how to monitor connectivity between nodes arises. We examine a connectivity protocol that guarantees that each side of a point-to-point connection sees the same history of activity over the communication channel. In other words, we maintain a consistent history of the state of the channel. The history of channel-state is guaranteed to be identical at each endpoint within some bounded slack. Our main contributions are: (i) a simple, stable protocol for monitoring connectivity that maintains a consistent history with bounded slack, and (ii) proofs that this protocol exhibits correctness, bounded slack, and stability.