Real-Time Replica Consistency over Ethernet with Reliability Bounds
Arpan Gujarati, Sergey Bozhko, Björn B. Brandenburg · 2020
Ethernet is expected to play a key role in the development of the next generation of safety-critical distributed real-time systems. Unfortunately, the use of switched Ethernet in place of traditional field buses such as CAN exposes systems to the risk of Byzantine errors (or inconsistent broadcasts) due to environmentally-induced transient faults.Byzantine fault tolerance (BFT) protocols can mitigate such errors to a large extent. However, no BFT protocol has yet been investigated from the perspective of hard real-time predictability. Classical Byzantine safety guarantees (e.g., 3f+ 1 processes can tolerate up to f Byzantine faults) are oblivious to non-uniform fault rates across different system components that arise due to environmental disturbances. Furthermore, existing analyses abstract from the underlying network topology despite its strong influence on actual failure rates.In this work, we present (i) a hard real-time interactive consistency protocol that allows distributed processes to agree on a common state despite Byzantine errors; and (ii) the first quantitative, real-time-aware reliability analysis of such a protocol deployed over switched Ethernet in the presence of stochastic transient faults. Our analysis is free of reliability anomalies and, as we show in our evaluation, can be used for a reliability-aware design space exploration of different fault tolerance alternatives.