Linear Time Byzantine Self-Stabilizing Clock Synchronization

Abstract

Awareness of the need for robustness in distributed systems increases as distributed systems become an integral part of day-to-day systems. Tolerating Byzantine faults and possessing self-stabilizing features are sensible and important requirements of distributed systems in general, and of a fundamental task such as clock synchronization in particular. There are efficient solutions for Byzantine non-stabilizing clock synchronization as well as for non-Byzantine self-stabilizing clock synchronization. In contrast, current Byzantine self-stabilizing clock synchronization algorithms have exponential convergence time and are thus impractical. We present a linear time Byzantine self-stabilizing clock synchronization algorithm, which thus makes this task feasible. Our deterministic clock synchronization algorithm is based on the observation that all clock synchronization algorithms require events for re-synchronizing the clock values. These events usually need to happen synchronously at the different nodes. In these solutions this is fulfilled or aided by having the clocks initially close to each other and thus the actual clock values can be used for synchronizing the events. This implies that clock values cannot differ arbitrarily, which necessarily renders these solutions to be non-stabilizing. Our scheme suggests using a tight pulse synchronization that is uncorrelated to the actual clock values. The synchronized pulses are used as the events for re-synchronizing the clock values.