The industrial communication market is dominated by Ethernet-based fieldbus systems. Although they share similar requirements and market segments, their implementations and ecosystems differ considerably. As a result, end customers and device manufacturers are faced with a multitude of technologies that need to be produced, run, diagnosed, maintained, and kept in stock. Although the availability of products and services is largely satisfactory, dealing with multiple solutions generates high costs and limits IoT capability. This paper introduces Open Platform Communication Unified Architecture Time-Sensitive Networking (OPC UA TSN) as a new technology and presents the current view. This time, the industrial prospects of fulfilling industrial communication requirements while leveraging the cost benefits of standard Ethernet hardware in the midterm are in reach. We anticipate that OPC UA TSN will reveal itself as a game changer in the field of industrial automation, being a candidate for establishing a holistic communication infrastructure from the sensor to the cloud.

An Introduction to OPC UA TSN for Industrial Communication Systems

White Rabbit (WR) extends the Precision Time Protocol (PTP) to provide synchronisation with sub-nanosecond accuracy and sub-50 picoseconds precision. The protocol aspects of the WR extension are currently studied and integrated into the upcoming revision of PTP. In the context of this PTP revision, mechanisms are added to allow the control of the Layer 1 (L1) syntonisation by the PTP protocol. This article focuses on the frequency transfer characteristics of the L1 syntonisation in WR. We first explain the interaction between L1 syntonisation and PTP synchronisation in a WR device and describe the architecture of its Phase-Locked Loop (PLL). We then characterize the frequency transfer through a WR network in two ways: measuring the characteristics of the WR switch according to the Synchronous Ethernet (SyncE) metrics defined in ITU-T G.8262, and performing phase noise analysis. The results of the measurements allow us to propose improvements that might be useful for different types of WR applications. Metrology laboratories might be interested in the optimisations made to significantly reduce the phase noise. On the other hand, the telecom industry might be interested in the modifications that make the WR switch SyncE-compliant but deteriorate its performance. Notably, the latter was achieved merely by modifying the software that implements the WR PLL.

White rabbit clock characteristics

Within the context of time dissemination techniques for power systems applications, this paper discusses the use of the white rabbit (WR) protocol for synchrophasor networks. Specifically, this paper presents a phasor measurement unit (PMU) integrating the WR technology and its experimental validation with a focus on the synchrophasor phase estimation in steady state conditions, by using a PMU calibrator generating the reference signals. We further compare the accuracy of the developed PMU with other state-of-the-art time synchronization technologies for PMUs, i.e., global positioning system (GPS) and precision time protocol (PTP), demonstrating applicability of WR for PMU sensing networks.

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The White Rabbit Time Synchronization Protocol for Synchrophasor Networks

This article provides a non-exhaustive overview of applications and enhancements to the White Rabbit (WR) extension of the IEEE 1588 Precision Time Protocol (PTP). Initially developed to serve accelerators at the European Or-ganization for Nuclear Research (CERN), WR has become a widely-used synchronization solution in scientific installations. This article classifies WR applications into five types, briefly explains each and describes example its installations. The article then summarizes WR enhancements that have been triggered by different applications and outlines WR’s integration into the PTP standard. Based on the presented variety of WR applications and enhancements, it concludes that WR will continue to proliferate in scientific applications and should soon find its way into industry.

White Rabbit Applications and Enhancements

Precise time synchronization becomes a vital constituent due to the rigorous needs of several time-sensitive applications. The clock synchronization protocol is one of the fundamental factors that can define the quality of communication. Our study starts with a brief discussion on the application domain of precise time synchronization and comes with an in-depth study of the synchronization with the main focus on the IEEE 1588 Precision Time Protocol (PTP). We have compared the well-known synchronization techniques and conclude that the PTP is the most appropriate answer to robust clock synchronization though challenges are there that requires thoughtful efforts and modification in the current version. The working mechanism and main components of the PTP network are discussed. We have established a testbench using commercially available devices and development boards to evaluate the PTP performance under different configurations. Major sources of synchronization error and other aspects contributing to precision are examined. This paper discussed numerous approaches that could enhance the performance of the PTP protocol. Structures for PTP based wireless clock synchronization required by advanced applications has also been discussed. In the end, paper focuses on the main industrial application areas in which PTP plays an important role, including WLAN, optical data centers, Smart grid, IEC 61850, etc. We conclude the paper by identifying the future trends and research directions for PTP based clock synchronization.

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IEEE 1588 for Clock Synchronization in Industrial IoT and Related Applications: A Review on Contributing Technologies, Protocols and Enhancement Methodologies

Various applications require or can benefit from high accuracy of synchronization between networked elements. The White Rabbit (WR) project includes enhancements to the now widespread IEEE1588 Precision Time Protocol (PTP) to support supplying synchronization in the sub-nanosecond level.

Enhanced synchronization accuracy in IEEE1588

Many network applications like motion control or precise monitoring of machines need precise knowledge about the time synchronization accuracy. But time synchronization accuracy depends on the performance of PTP nodes, network topology, environmental conditions and various other factors. This makes the determination of synchronization accuracy a complex task. A mechanism for determining the worst case synchronization accuracy is defined in the PTP Power Profile. A TLV is used for accumulating a vendor defined worst case inaccuracy. However in practice when using this approach the inaccuracy values are often much higher than the real synchronization accuracy. In this paper, a technique for automatic determination of synchronization path quality is investigated. It utilizes PTP Bridges with an inaccuracy estimation performed using an inaccuracy model that is separated into static and dynamic inaccuracy contributors. One assumption is that the inaccuracy in the PTP time observed by a bridge, depends on the position of the bridge in the sync path. The latter is due to accumulation of more, possibly independent, random contributors. The effect of increasing deviation is modeled and verified using an experimental setup. The paper concludes that detailed knowledge about the PTP network (cable lengths, inaccuracy contribution metrics for the specific nodes within the sync path, etc.) are useful for automatic determination of the synchronization path quality, synchronization monitoring, system configuration and diagnosis. We suggest an enhancement to the TimeInaccuracy TLV that may possibly be incorporated within the next PTP revision, to better facilitate the protocol support for the above functions.

Automatic determination of synchronization path quality using PTP bridges with integrated inaccuracy estimation for system configuration and monitoring

The IEEE1588-2008 (precision time protocol, PTP) is being deployed in various application domains including domains requiring specified synchronization performance. Deploying appropriately defined monitoring functions will support the continuous operation of synchronization networks at the required synchronization quality. The paper addresses the field of synchronization monitoring, first introducing the relevant background. It shortly reviews synchronization quality performance criteria and possible measurement metrics. This is followed by a review and analysis of synchronization performance factors and possible failure points. Synchronization monitoring functions addressing the various factors are defined and shortly described. The paper elaborates in more detail on the packet delay variation monitoring and node performance monitoring functions. Finally, a possible extension to the PTP standard increasing and simplifying support for slave performance monitoring and testing is described.

Synchronization monitoring in IEEE1588 synchronization networks

A method for use in connection with a data transmission network includes receiving a plurality of time interval error data samples over a sampling period and comparing a duration of the sampling period to a time threshold for the sampling period. If the duration of the sampling period is less than or equal to the time threshold for the sampling period, the method includes processing the received plurality of data samples so as to calculate in real time a maximum time interval error. However, if the duration of the sampling period exceeds the time threshold for the sampling period, the method includes dividing the sampling period into a finite number of sub-intervals and processing the data samples in each sub-interval so as to produce a respective intermediate result for each sub-interval. Each of these intermediate results is stored directly after it is produced, and these stored intermediate results are processed so as to estimate the maximum time interval error.

Opher Ronen

Papers

Enhanced synchronization accuracy in IEEE1588

Automatic determination of synchronization path quality using PTP bridges with integrated inaccuracy estimation for system configuration and monitoring

Synchronization monitoring in IEEE1588 synchronization networks

Method and apparatus for estimating a maximum time interval error in a data transmission network