IEEE 1588 Research Articles

High-precision time synchronization chip design for industrial sensor and actuator network

Mission-critical (MC) sensor and actuator networks (SANs) are being applied widely for multiaxis motion control of robotic manipulators , particularly for performing MC tasks in smart manufacturing. One of the most challenging tasks in MC-SANs is the development of a precision time synchronization (PTS) protocol. A conventional precision time system uses the IEEE 1588 v2 standard [1] ; however, in MC-SANs, many factors need to be considered when designing an IoT computing system, such as robustness, cost-effectiveness, interoperability and scalability. This study proposes a high-precision time synchronization protocol based on Modbus sensors and actuator networks for an industrial fieldbus network. The PTS protocol design and hardware synthesis are conducted with a consistent and systematic design methodology. GRAFCET is used to model the individual functional modules and hierarchical behavior of the system. The behavior of each module is represented as a sequential–concurrent hybrid discrete event system . We apply high-level synthesis rules to design PTS hardware for a complex PTS system based on the VHSIC hardware description language (VHDL). The PTS hardware module has an embedded PTS algorithm with a proportional error correction model, and the time synchronization accuracy of the precision time protocol (PTP) chip is up to 42 ns. Experimental results demonstrate that our high-performance PTS controller chip can satisfy the requirements of multiaxis motion control and that it is more efficient than other protocols and products designed for similar industrial manufacturing applications.

Multichannel Time Synchronization Based on PTP through a High Voltage Isolation Buffer Network Interface for Thick-GEM Detectors

Data logging and complex algorithm implementations acting on multichannel systems with independent devices require the use of time synchronization. In the case of Gas Electron Multipliers (GEM) and Thick-GEM (THGEM) detectors, the biasing potential can be generated at the detector level via DC to DC converters operating at floating voltage. In this case, high voltage isolation buffers may be used to allow communication between the different channels. However, their use add non-negligible delays in the transmission channel, complicating the synchronization. Implementation of a simplified precise time protocol is presented for handling the synchronization on the Field Programmable Gate Array (FPGA) side of a Xilinx SoC Zynq ZC7Z030. The synchronization is done through a high voltage isolated bidirectional network interface built on a custom board attached to a commercial CIAA_ACC carrier. The results of the synchronization are shown through oscilloscope captures measuring the time drift over long periods of time, achieving synchronization in the order of nanoseconds.

A 500-km Cascaded White Rabbit Link for High-Performance Frequency Dissemination.

We perform experiments exploring the use of white rabbit precision time protocol (WR-PTP) for time and frequency dissemination over long-distance optical fiber links. We use unidirectional links, to ensure compatibility with active telecommunication networks, and White Rabbit equipment with modifications for improved performance. Using fiber spools, we realize a 500 km, four-span cascaded white rabbit link. We show short term fractional frequency stability of 2×10-12 , averaging down to 2×10-15 at one day of integration time, with no frequency shift within the statistical uncertainty. We demonstrate the impact of increasing the White Rabbit SoftPLL bandwidth and the PTP message rate. We show evidence of the effect of thermal fluctuations acting on the fiber, and finally discuss the limitations of the achieved performance. We show comparisons with experimental data acquired with commercial good quality global positioning system (GPS) receivers and show that the medium- and long- term stability and accuracy are more than one order of magnitude better with a WR-PTP link.

Network Synchronization Revisited: Time Delays in Mutually Coupled Oscillators

Coordinated and efficient operation in large, complex systems requires the synchronization of the rhythms of spatially distributed components. Such systems are the basis for critical infrastructure such as satellite navigation, mobile communications, and services like the precision time protocol and Universal Coordinated Time. Different concepts for the synchronization of oscillator networks have been proposed, in particular mutual synchronization without and hierarchical synchronization from a reference clock. Established network synchronization models in electrical engineering address the role of inevitable cross-coupling time delays for network synchronization. Mutual synchronization has been studied using linear approximations of the coupling functions of these models. We review previous work and present a general model in which we study synchronization taking into account nonlinearities and finite time delays. As a result, dynamical phenomena in networks of coupled electronic oscillators induced by time delays, such as the multistability and stabilization of synchronized states can be predicted and observed. We study the linear stability of nonlinear states and predict for which system parameters synchronized states can be stable. We use these results to discuss the implementation of mutual synchronization for complex system architectures. A key finding is that mutual synchronization can result in stable in- and anti-phase synchronized states in the presence of large time delays. We provide the condition for which such synchronized states are guaranteed to be stable.

Highly Accurate Pose Estimation as a Reference for Autonomous Vehicles in Near-Range Scenarios

To validate the accuracy and reliability of onboard sensors for object detection and localization for driver assistance, as well as autonomous driving applications under realistic conditions (indoors and outdoors), a novel tracking system is presented. This tracking system is developed to determine the position and orientation of a slow-moving vehicle during test maneuvers within a reference environment (e.g., car during parking maneuvers), independent of the onboard sensors. One requirement is a 6 degree of freedom (DoF) pose with position uncertainty below 5 mm (3σ), orientation uncertainty below 0.3° (3σ), at a frequency higher than 20 Hz, and with a latency smaller than 500 ms. To compare the results from the reference system with the vehicle’s onboard system, synchronization via a Precision Time Protocol (PTP) and system interoperability to a robot operating system (ROS) are achieved. The developed system combines motion capture cameras mounted in a 360° panorama view setup on the vehicle, measuring retroreflective markers distributed over the test site with known coordinates, while robotic total stations measure a prism on the vehicle. A point cloud of the test site serves as a digital twin of the environment, in which the movement of the vehicle is visualized. The results have shown that the fused measurements of these sensors complement each other, so that the accuracy requirements for the 6 DoF pose can be met while allowing a flexible installation in different environments.

Means and Methods of Efficiency Estimation of Video Stream Transmission Based on GigE Vision Technology Using Application Processor

The paper investigates the possibility of efficient implementation of a GigE Vision compatible video stream source on a computing platform based on a system-on-a-chip with general-purpose ARM processor cores. In particular, to implement the aforementioned video source, a proprietary prototype of a GigE Vision compatible camera was developed based on the Raspberry Pi 4 single-board computer. This computing platform was chosen due to its widespread use and wide community support. The software part of the camera is implemented using the Video4Linux and Aravis libraries. The first library is used for the primary image capturing from a video sensor connected to a single board computer. The second library is intended for forming and transmission of video stream frames compatible with GigE Vision technology over the network. To estimate the delays in the transmission of a video stream over an Ethernet channel, a methodology based on the Precise Time Protocol (PTP) has been proposed and applied. During the experiments, it was found that the software implementation of a GigE Vision compatible camera on single-board computers with general-purpose processor cores is quite promising. Without additional optimization, such an implementation can be successfully used to transmit small frames (with a resolution of up to 640 × 480 pixels), giving a delay less than 10 ms. At the same time, some additional optimizations may be required to transmit larger frames. Namely, a MTU (maximum transmission unit) size value plays the crucial role in latency formation. Thus, to implement a faster camera, it is necessary to select a platform that supports the largest possible MTU (unfortunately, it turned out that it is not possible with Raspberry Pi 4, as it supports relatively small MTU size of up to 2000 bytes). In addition, the image format conversion procedure can noticeably affect the delay. Therefore, it is highly desirable to avoid any frame processing on the transmitter side and, if it is possible, to broadcast raw images. If the conversion of the frame format is necessary, the platform should be chosen so that there are free computing cores on it, which will permit to distribute all necessary frame conversions between these cores using parallelization techniques.

A Novel Clock Skew Estimator and Its Performance for the IEEE 1588v2 (PTP) Case in Fractional Gaussian Noise/Generalized Fractional Gaussian Noise Environment

Papers in the literature dealing with the Ethernet network characterize packet delay variation (PDV) as a long-range dependence (LRD) process. Fractional Gaussian noise (fGn) or generalized fraction Gaussian noise (gfGn) belong to the LRD process. This paper proposes a novel clock skew estimator for the IEEE1588v2 applicable for the white-Gaussian, fGn, or gfGn environment. The clock skew estimator does not depend on the unknown asymmetry between the fixed delays in the forward and reverse paths nor on the clock offset between the Master and Slave. In addition, we supply a closed-form-approximated expression for the mean square error (MSE) related to our new proposed clock skew estimator. This expression is a function of the Hurst exponent H, as a function of the parameter a for the gfGn case, as a function of the total sent Sync messages, as a function of the Sync period, and as a function of the PDV variances of the forward and reverse paths. Simulation results confirm that our closed-form-approximated expression for the MSE indeed supplies the performance of our new proposed clock skew estimator efficiently for various values of the Hurst exponent, for the parameter a in gfGn case, for different Sync periods, for various values for the number of Sync periods and for various values for the PDV variances of the forward and reverse paths. Simulation results also show the advantage in the performance of our new proposed clock skew estimator compared to the literature known ML-like estimator (MLLE) that maximizes the likelihood function obtained based on a reduced subset of observations (the first and last timing stamps). This paper also presents designing graphs for the system designer that show the number of the Sync periods needed to get the required clock skew performance (MSE = 10–12). Thus, the system designer can approximately know in advance the total delay or the time the system has to wait until getting the required system’s performance from the MSE point of view.

CoSiWiNeT: A Clock Synchronization Algorithm for Wide Area IIoT Network

Recent advances in the industrial internet of things (IIoT) and cyber–physical systems drive Industry 4.0 and have led to remote monitoring and control applications that require factories to be connected to remote sites over wide area networks (WAN). The adequate performance of remote applications depends on the use of a clock synchronization scheme. Packet delay variations adversely impact the clock synchronization performance. This impact is significant in WAN as it comprises wired and wireless segments belonging to public and private networks, and such heterogeneity results in inconsistent delays. Highly accurate, hardware–based time synchronization solutions, global positioning system (GPS), and precision time protocol (PTP) are not preferred in WAN due to cost, environmental effects, hardware failure modes, and reliability issues. As a software–based network time protocol (NTP) overcomes these challenges but lacks accuracy, the authors propose a software–based clock synchronization method, called CoSiWiNeT, based on the random sample consensus (RANSAC) algorithm that uses an iterative technique to estimate a correct offset from observed noisy data. To evaluate the algorithm’s performance, measurements captured in a WAN deployed within two cities were used in the simulation. The results show that the performance of the new algorithm matches well with NTP and state–of–the–art methods in good network conditions; however, it outperforms them in degrading network scenarios.

Design and FPGA based Implementation of IEEE 1588 Precision Time Protocol for Synchronisation in Distributed IoT Applications

ABSTRACT In distributed network applications such as the Internet of Things (IoT), a master clock is used to provide a frame of reference among all constituent nodes. Any drift in the clock on a single node can cause serious cascading effects in a system that largely involves ordered events and time-critical tasks. To provide a stable reference clock, time synchronisation protocols are utilised in distributed systems where client nodes can synchronise their clock with a master node. IEEE 1588 Precision Time Protocol (PTP) is increasingly being used to provide high time synchronisation accuracy in comparison with other synchronisation protocols. In this paper, we have proposed a hardware design and FPGA-based implementation of the IEEE 1588 protocol to be used in wired LAN communication. Experimental results show synchronisation accuracy in the range of few nanoseconds, which is significantly better than the existing implementations. The FPGA implementation was carried out on a Xilinx Artix-7 evaluation board.

Sub-nanosecond synchronization implementation in pure Xilinx Kintex-7 FPGA

White Rabbit (WR) provides high-performance synchronization with sub-nanosecond accuracy and picoseconds precision, and it has been included in the new High Accuracy Default PTP Profile in the IEEE 1588-2019. As an open-source project, WR Precision Time Protocol (WR-PTP) core has been implemented in different FPGA platforms with dedicated clock circuits. This paper presents a novel approach to achieve the WR function in Xilinx Kintex-7 FPGA depending on the on-chip resource. This approach could achieve sub-nanosecond accuracy and tens of picoseconds precision, simplifying WR devices' hardware design and making it possible to port the WR PTP core to many mature hardware platforms.

Implementing Time-triggered Communication for Embedded Ethernet Real-time Network using IEEE 1588 Time Synchronization

A time-triggered embedded system has become a ubiquitous technique in safety-critical systems, such as automotive, aerospace, and medical sectors. Thus, precision is of utmost importance to determine if the application is synchronized correctly. The Network Time Protocol is the traditional protocol used for clock synchronization in wired networks. On the other hand, the protocol lacks hardware timestamping features, and it collects many timestamping errors because of the diversification of the queuing time in the switches and router. This drawback was implemented into a new protocol, and new features on the Precision Time Protocol, known as IEEE 1588-2008, were added. This paper proposes a real-time network for a time-triggered Embedded system, the Precision Time Protocol synchronize, on a Spartan 3E Field Programmable Gate Array (FPGA). Two approaches were also introduced to evaluate the performance using Precision Time Protocol: hardware and software implementations. MATLAB Simulink software was used to evaluate the software approaches. The result showed that the Precision Time Protocol used 0.83μs to complete the clock synchronization compared to the 4.65μs used by the Network Time Protocol, which was six times faster.

Monitoring of Energy Data with Seamless Temporal Accuracy Based on the Time-Sensitive Networking Standard and Enhanced µPMUs

In the energy sector, distributed synchronism and a high degree of stability are necessary for all real-time monitoring and control systems. Instantaneous response to critical situations is essential for the integration of renewable energies. The most widely used standards for clock synchronisation, such as Network Time Protocol (NTP) and Precision Time Protocol (PTP), do not allow for achieving synchronised simultaneous sampling in distributed systems. In this work, a novel distributed synchronism system based on the Time-Sensitive Networking (TSN) standard has been validated for its integration in an architecture oriented towards the high-resolution digitisation of photovoltaic (PV) generation systems. This method guarantees a time stamping with an optimal resolution that allows for the analysis of the influence of fast-evolving atmospheric fluctuations in several plants located in the same geographical area. This paper proposes an enhanced micro-phasor measurement unit (µPMU) that acts as a phasor meter and TSN master controlling the monitoring system synchronism. With this technique, the synchronism would be extended to the remaining measurement systems that would be involved in the installation at distances greater than 100 m. Several analyses were carried out with an on-line topology of four acquisition systems capturing simultaneously. The influence of the Ethernet network and the transducers involved in the acquisition process were studied. Tests were performed with Ethernet cable lengths of 2, 10, 50, and 75 m. The results were validated with 24-bit Sigma-Delta converters and high-precision resistor networks specialised in high-voltage monitoring. It was observed that with an appropriate choice of sensors and TSN synchronism, phase errors of less than ±1 µs can be guaranteed by performing distributed captures up to 50 kS/s. Statistical analysis showed that uncertainties of less than ±100 ns were achieved with 16-bit Successive Approximation Register (SAR) converters at a moderate cost. Finally, the requirements of the IEEE C37.118.1-2011 standard for phasor measurement units (PMU) were also satisfied. This standard establishes an uncertainty of ±3.1 μs for 50 Hz systems. These results demonstrate the feasibility of implementing a simultaneous sampling system for distributed acquisition systems coordinated by a µPMU.

Trusted GNSS-Based Time Synchronization for Industry 4.0 Applications

The protection of satellite-derived timing information is becoming a fundamental requirement in Industry 4.0 applications, as well as in a growing number of critical infrastructures. All the industrial systems where several nodes or devices communicate and/or coordinate their functionalities by means of a communication network need accurate, reliable and trusted time synchronization. For instance, the correct operation of automation and control systems, measurement and automatic test systems, power generation, transmission, and distribution typically require a sub-microsecond time accuracy. This paper analyses the main attack vectors and stresses the need for software integrity control at network nodes of Industry 4.0 applications to complement existing security solutions that focus on Global Navigation Satellite System (GNSS) radio-frequency spectrum and Precision Time Protocol (PTP), also known as IEEE-1588. A real implementation of a Software Integrity Architecture in accordance with Trusted Computing principles concludes the work, together with the presentation of promising results obtained with a flexible and reconfigurable testbed for hands-on activities.

Measuring Network Conditions in Data Centers Using the Precision Time Protocol

Increased network latency and packets losses can affect substantially application performance. Due to the scale of data centers, custom network monitoring tools have been developed to measure network latency and packet loss. In this paper, we use the Precision Time Protocol (PTP) to estimate one-way delay and to quantify packet loss ratios. We propose PTPmesh as a cloud network monitoring tool which uses PTPd as a building block. We present an analysis of PTPmesh latency and packet loss measurements collected in ten data centers from three cloud providers. Our findings reveal different latency, latency variance, packet loss and path symmetry characteristics across data centers. To foster further research in this area, we make our dataset available at Popescu and Moore (2018).

Recent Advances in Precision Clock Synchronization Protocols for Power Grid Control Systems

With the advent of a new Precision Time Protocol specification, new opportunities abound for clock synchronization possibilities within power grid control systems. The third iteration of the Institute of Electrical and Electronics Engineers Standard 1588 specification provides several new features specifically aimed at complex, wide-area deployments in which situational awareness and control require precise time agreement. This paper describes the challenges faced by existing technology, introduces the new time distribution specification, and provides examples to explain how it represents a game-changing innovation.

Chained Data Acquisition and Transmission System Protype for Cabled Seafloor Earthquake Observatory

Seafloor observatories can provide long-term, real-time submarine monitoring data, which has great significance for the study of major scientific technology in marine science, especially in the seafloor earthquake observation. The chained submarine data sampling and transmission system is the prototype and foundation of cabled seafloor earthquake observatories. This paper designs and builds a chained data sampling and transmission system (SQSTS) based on Zynq-7000 Soc (System on chip) and clock synchronization. At the beginning, we realized high-precision submarine data (24 bit) sampling based on Zynq-7000 Soc and ADS 1256. Using the PPS (Pulse per second) signal provided by the P88 1588 PTP (Precise time protocol) clock synchronization board and the inner crystal oscillator of the Zynq-7000 Soc, the time stamp up to the microsecond level, for the seismic data sampled in each seismometer node can support subsequent inversion of seismic data. In addition, a high-speed data transmission link connecting nodes in SQSTS, which is based on the Gigabit transceiver and optical cable, has been investigated. The transmission link has been realized by using the Aurora IP core. The theoretical calculations indicate that the data transmission bus bandwidth can reach 4 Gbps, while in the meantime its reliability has been proved by experiments. The experimental results show that the system owns the characteristics of high data sampling accuracy, stable and reliable high-speed transmission, and has promising application prospects.

White Rabbit Time Synchronization for Radiation Detector Readout Electronics

As radiation detector arrays in nuclear physics applications become larger and physically more separated, the time synchronization and trigger distribution between many channels of detector readout electronics become more challenging. Clocks and triggers are traditionally distributed through dedicated cabling, but newer methods such as the IEEE 1588 Precision Time Protocol and White Rabbit allow clock synchronization through the exchange of timing messages over Ethernet. Consequently, we report here the use of White Rabbit in a new detector readout module, the Pixie-Net XL. The White Rabbit core, data capture from multiple digitizing channels, and subsequent pulse processing for pulse height and constant fraction timing are implemented in a Kintex 7 FPGA. The detector data records include White Rabbit time stamps and are transmitted to storage through the White Rabbit core's gigabit Ethernet data path or a slower diagnostic/control link using an embedded Zynq processor. The performance is characterized by time-of-flight style measurements and by time correlation of high energy background events from cosmic showers in detectors separated by longer distances. Software for the Zynq processor can implement "software triggering", for example to limit recording of data to events where a minimum number of channels from multiple modules detect radiation at the same time.

A Multipronged Approach to Effectively Secure SMPTE ST 2059 Time Transfer

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">The transition from serial digital interface (SDI) to the All-IP studio has been happening more frequently, with numerous broadcasting facilities partly, or even exclusively, relying on this new technology. Accurate and reliable synchronization is a mandatory requirement for every broadcasting studio. Consequently, packet-based time transfer over Ethernet evolved into a crucial building block. The Precision Time Protocol (PTP) has proved time and again that it can deliver the required accuracy of less than</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\mu \text{s}$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">regardless of the size and topology of the underlying network. Its inherent fault tolerance is limited and thus insufficient to fulfill the stringent requirements of the broadcasting industry in that respect. Thus, it has to be extended to a highly robust and resilient time transfer technology by applying a series of enhancements. This paper presents various ways of significantly improving the resilience of PTP including an in-depth analysis of failures caused by malfunctioning or misconfigured devices as well as malicious attacks. The latter should be investigated independently because PTP itself is vulnerable to such attacks. Countermeasures for all major fault conditions are presented together with their potential impacts on time transfer. Realworld examples with typical failure conditions and their effects on accuracy, both locally and systemwide, are given. Methods on how to prevent these failures altogether or at least detect them reliably thus being able to issue adequate countermeasures without delay are discussed as well. The paper concludes by presenting ways the broadcasting industry can benefit from these new features efficiently and quickly</i> .

Monitoring and Analysis of SMPTE ST 2059-2 PTP Networks and Media Devices

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">As All-IP studios leveraging the SMPTE ST 2110 document suite gain traction, one of the fundamental pillars upon which such systems rely is an accurate and reliable time transfer protocol. SMPTE ST 2059 standardized such a model based on the IEEE 1588 Precision Time Protocol (PTP). Every element, whether it be network or media devices, impacts the overall time transfer accuracy. This impacts the timing of the ST 2110 media streams that are generated or received by the media nodes. While PTP does provide fault tolerance capabilities, performance degradation of time transfer is not always well understood. This can significantly impact operations in live networks, it being due to a sudden event or a degradation over time. Therefore, an overarching view of the end-to-end timing system including backup, standby, and network devices is required. Monitoring of such capabilities should be common to all devices, whenever possible, including different means to verify in-band and out-of-band measurements as to how devices are performing, with respect to time transfer. Combined with historical archiving of the monitored data, this provides the framework for tracking and correlating possible events. This paper describes the different monitoring capabilities, their advantages and weaknesses, and the value they provide to the monitored datasets. It further focuses on the means to make the process uniform across all monitored devices to ensure consistency in the collected data. Finally, we discuss the ongoing efforts in SMPTE and other standardization bodies around PTP monitoring, the common trends, expected outcomes, and how these will contribute to streamlining time transfer monitoring, supervision, and analysis</i> .

A new delay attack detection algorithm for PTP network in power substation

Time synchronization is one of the main issues for guaranteeing the correctness of actions depending on the time of measured data or detected events by electronic devices across industrial networks. According to the accuracy needed in different applications and networks, several synchronization protocols or algorithms have been proposed so far. The Precision Time Protocol, PTP, is one of the most accurate synchronization protocols introduced for automation applications. It has also been used in power grids and digital substations. However, due to the variety of cyber-attacks in electrical power systems in recent years, its security should be considered and evaluated as other substation components. This paper introduces a new PTP attack detection algorithm. The proposed algorithm can detect delay attacks on Sync messages as well as attacks on transparent clocks and simultaneous attacks on the network. The efficiency and advantages of the proposed algorithm over other methods are verified through mathematical analysis as well as several simulations.