Klaus Schossmaier

Interval-based Clock Synchronization

In this paper, we develop and analyze a simple interval-based algorithm suitable for fault-tolerant external clock synchronization. Unlike usual internal synchronization approaches, our convergence function-based algorithm provides approximately synchronized clocks maintaining both precision and accuracy w.r.t. external time. This is accomplished by means of a time representation relying on intervals that capture external time, providing accuracy information encoded in interval lengths. The algorithm, which is generic w.r.t. the convergence function and relies on either instantaneous correction or continuous amortization for clock adjustment, is analyzed by utilizing a novel, interval-based framework for establishing worst-case precision and accuracy bounds subject to a fairly detailed system model. Apart from individual clock rate and transmission delay bounds, our system model incorporates non-standard features like clock granularity and broadcast latencies as well. Relying on a suitable notion of internal global time, our analysis unifies treatment of precision and accuracy, ending up in striking conceptual beauty and expressive power.

How to reconcile fault-tolerant interval intersection with the Lipschitz condition

Summary. We present a new fault-tolerant intersection function

Specification and Implementation of the Universal TimeCoordinated Synchronization Unit (UTCSU)

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An interval-based framework for clock rate synchronization

, which satisfies the Lipschitz condition for the uniform metric and is optimal among all functions with this property.

An algorithm for fault-tolerant clock state & rate synchronization

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NTI: A Network Time Interface M-module for high-accuracy clock synchronization

thus settles Lamports question about such a function raised in [5]. Our comprehensive analysis reveals that

An ASIC supporting external clock synchronization for distributed real-time systems

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The SimUTC fault-tolerant distributed systems simulation toolkit

has exactly the same worst-case performance as the optimal Marzullo function

PSynUTC - Evaluation of a High Precision Time Synchronization Prototype System for Ethernet LANs

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UTCSU Functional Specification

, which does not satisfy a Lipschitz condition. The utilized modelling approach in conjunction with a powerful hybrid fault model ensures compatibility of our results with any known application framework, including replicated sensors and clock synchronization.