A Kad Prototype for Time Synchronization in Real-Time Automation Scenarios

Inhalt:
In this paper, a prototype to synchronize the Peer-to-Peer network Kad is presented. The approach bases on a deterministic algorithm, which is required for hard real-time applications, to synchronize the network in a decentralized manner. Existing industrial Ethernet solutions include and support real-time capable machine-to-machine communication in automation scenarios. However, the coordination of the communication and the synchronization to achieve hard real-time are managed by a central instance, leading to deficient resilience and scalability. Additionally, a centralized or hierarchical synchronization is required to enable the communication per se. The presented decentralized synchronization instead benefits from nodes helping to synchronize the network and bases on the decentralized structured Peer-to-Peer network Kad. However, the higher the number of helping nodes the higher is the time deviation on the nodes of the network, which contrary results in a higher time error. Therefore, a trade-off between synchronization performance and time error has to be determined to meet predefined constraints depending on the application scenario. Moreover, the individual clock drift of every device needs to be considered to define necessary re-synchronization intervals of the network. Theoretical values are compared to the measured values determined in experiments with 15 nodes. As a result of these experiments, the measured synchronization performance, which is the time needed to synchronize the complete network, confirms the theoretical worst case values. The result is a running prototype system, which is able to synchronize the network with a high performance in a decentralized manner.