Transparent clock characterization using IEEE 1588 PTP timestamping probe

As new application areas like SmartGrids and 4G cellular mobile backhaul networks emerge, requirements on precision of the frequency and time synchronization increase. IEEE 1588v2 Precision Time Protocol (PTP) offers sub-microsecond synchronization precision using conventional Ethernet networks. In practical network scenarios the PTP performance is greatly reduced due to varying queuing latencies introduced by the network´s switching and routing devices. This drawback has been overcome with the introduction of network devices with a Transparent Clock (TC) functionality defined in the IEEE 1588v2 PTP standard. As different vendors use proprietary implementations of the TC mechanism, it becomes essential to characterize TC´s accuracy. Literature survey revealed that so far two measurement techniques have been proposed for that purpose, however, a comprehensive study of the measurement´s error with regards to hardware imprecisions have not yet been published. In this paper we provide a thorough mathematical analysis with respect to hardware limitations of the TC measurement techniques and based on this analysis measurement calibrations are introduced. Moreover, we propose a new measurement setup that requires less expensive hardware yet maintains similar precision to prior art techniques. The new setup is provided with a detailed proof of concept and an experimental verification through measurements.