A composable algorithm for clock synchronization in multi-cluster real-time systems

In a previous work we have shown that by deploying a node with a high-quality oscillator (rate-master node) in each cluster of a real-time system, we can integrate internal and external clock synchronization by a combination of a distributed mechanism for clock state synchronization with a central mechanism for clock rate synchronization. By means of hardware and simulation experiments we have shown that this combination improves the precision of the global time base in single- and multi-cluster systems while reducing the need for high-quality oscillators for non-rate-master nodes. In the original approach all nodes, including the rate-master node, execute a fault-tolerant internal clock synchronization algorithm in course of which all nodes periodically adjust their local clocks by means of clock state correction. In this paper we analyze a derivative of the original algorithm in which the rate-master node does not take part in the internal clock synchronization algorithm. We study and discuss this approach for clock synchronization with regard to cluster precision, cluster drift rate and non-interference with external clock synchronization and multi-cluster clock synchronization.