Synchrony/Asynchrony vs. Stationary/Mobile? The Latter is Superior...in Theory

TL;DR

This paper demonstrates that in distributed systems, mobility of faults allows consensus to be solvable in models where asynchrony alone would prevent it, highlighting the potential advantages of mobility.

Contribution

It introduces and analyzes the mobile analogue of asynchronous models, showing that mobility can enable consensus where asynchrony cannot, and establishes a relationship with binary Commit-Adopt.

Findings

Consensus is solvable in mobile analogues even when not in asynchronous models.

Mobility of faults can make consensus achievable in systems where asynchrony prevents it.

The paper establishes a case-by-case equivalence between consensus solvability and binary Commit-Adopt in mobile models.

Abstract

Like Asynchrony, Mobility of faults precludes consensus. Yet, a model M in which Consensus is solvable, has an analogue relaxed model in which Consensus is not solvable and for which we can ask, whether Consensus is solvable if the system initially behaves like the relaxed analogue model, but eventually morphs into M. We consider two relaxed analogues of M. The first is the traditional Asynchronous model, and the second to be defined, the Mobile analogue. While for some M we show that Consensus is not solvable in the Asynchronous analogue, it is solvable in all the Mobile analogues. Hence, from this perspective Mobility is superior to Asynchrony. The pie in the sky relationship we envision is: Consensus is solvable in M, if and only if binary Commit-Adopt is solvable in the mobile analogue. The ``only if'' is easy. Here we show case by case that the ``if'' holds for all the common faults types.