[Back]

M. Paulitsch, P. Puschner:
"Non-Interfering Multi-Cluster Clock Synchronization";
2002.

Large-scale distributed fault-tolerant real-time systems typically consist of a number of clusters, i.e., groups of closely interacting computing nodes, that are, in turn, connected to multi-cluster systems. To be able to act in synchrony, the nodes of a multi-cluster system need a common time base. Internal clock synchronization synchronizes the nodes within clusters, while external clock synchronization is used to synchronize the virtual-time representations of different clusters.
This paper shows that a cluster of a multi-cluster system can be externally synchronized to the other clusters, such that the precision of the externally synchronized time on the cluster depends only on cluster-internal parameters, i.e., parameters that are outside the sphere of control of the cluster do not affect the precision. On top of being independent of cluster-external parameters, the precision of the externally synchronized time is only negligibly worse than the precision achievable by the internal clock synchronization of the cluster.

As the presented multi-cluster clock synchronization allows the composition of clusters while ensuring a stable time base at each of the clusters, it establishes the basis for the temporal composability of clusters. The precision of the single clusters, which is the driving factor for the minimum granularity of a time base, does only insignificantly change when different, independently developed clusters with different virtual-clock parameters are composed to a multi-cluster system. The implementation of the proposed clock-synchronization algorithm and experiments confirm these findings.

http://www.vmars.tuwien.ac.at/php/pserver/extern/docdetail.php?DID=806&viewmode=paper&year=2002