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H. Kopetz, A. Ademaj, A. Hanzlik:
"Integration of Internal and External Clock Synchronization by the Combination of Clock-State and Clock-Rate Correction in Fault-Tolerant Distributed Systems";
Talk: IEEE Real-Time Systems Symposium, Lisbon, Portugal; 2004-12-05 - 2004-12-08; in: "Proceedings of the 25th IEEE International Real-Time Systems Symposium", IEEE, (2004), ISBN: 0-7695-2247-5.

This paper proposes a combination of a fault-tolerant distributed algorithm for clock state correction
with a fault-tolerant algorithm for clock rate correction in order to improve the precision
of the global time base in a distributed computing system while reducing the need for high-quality
oscillators. The state correction part compensates the drift rates and achieves a synchronization
of distributed clocks within a specified precision. The rate correction part of the algorithm contributes
to a much tighter synchronization by eliminating systematic rate errors. A failure in
the clock rate correction will not hinder the distributed fault-tolerant clock state synchronization
algorithm, since the state correction operates independently from the rate correction. It is shown
that these combined algorithms are also ideally suited to solve the problem of external clock
synchronization in multi-cluster systems. The paper introduces new algorithms and presents
experimental results on the achieved improvements in the precision measured in a TTP cluster.
Results of simulation experiments of the new algorithms in single-cluster and multi-cluster
configurations are also presented.

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