Experimental assessment of a JANUS-based consensus protocol

This paper proposes a distributed, JANUS-based protocol that enables an underwater acoustic network to reach consensus on arbitrary local opinions as numeric state variables. An envisioned scenario where nodes shall agree on parameters describing the acoustic environment is used to evaluate the protocol. The scenario exemplifies the protocol's potential in future applications where nodes use the environment description to decide on appropriate modulation and coding schemes. The evaluation is based on numerical simulations and sea experiments in a challenging acoustic environment. The numerical simulations allowed examining the performance for different parameter values regarding the timing of transmission events and state transitions in the finite state machine implementation of the protocol. The best parameter configuration was used in the sea experiments conducted in a bay in the Baltic Sea. The experiments comprised several deployments of five to six commercial modems. Results from the experiments show that the protocol can achieve a consensus up to 89% of the time in the tested environment, and up to 96% of the time if the state variables are permitted to differ by one discretisation step maximum across the network. In addition, if the network separates due to environmental conditions, connected components appear to achieve consensus more often when the links are more reliable. Finally, it is shown that when different consensus processes are active in parallel, packets from one process do not interfere with the opinions in different processes, besides the existing probability of packet loss due to packet collision.