On the Evaluation of Clock Synchronization Methods for Networked Control Systems

A distribute control requires to maintain time synchronization with a degree of precision depending on a  particular application domain. Many large distributed systems employ Ethernet or even full TCP/IP stack for communication. Two prevalent protocols are used for clock synchronization in these networks, in particular, Network Time Protocol (NTP)  and Precise Time Protocol (PTP). In this short paper, we present a method for  practical performance evaluation of clock synchronization within a distributed environment based on the QNX real time operating system. For the measurement we consider nodes  that are assumed to produce synchronous signals. The results of measurement provide a hint on the degree of synchronization that can be practically reached among the set of distributed devices. To be able to perform NTP and PTP  benchmarking, we ported PTPd Unix/Linux implementation to QNX operating system. We prepared an environment to compare NTP and PTP behavior in different network topologies and under different network load characteristic.  The main contribution of this paper is to provide an overview of a method for practical evaluation of synchronization methods for a distributed control system. We present some preliminary results from the measurement. A complete result set may be used, e.g., for defining a performance estimation function in a platform-based design methods.