Search

With the continuing spread of distributed measurement and control systems (e.g. Cyber-Physical Systems, Industry 4.0) there is an increased need to implement synchronized sampling and actuation over the components of a distributed system. To achieve this goal, the clocks of the system must be synchronized, including the ones doing sampling and actuation. In most cases local synchronization alone is not enough; It is also needed to keep in sync with a global reference time in order, for example, to be able to implement timestamps based on global time and simultaneous sampling across system components that are spatially distributed (operate on different sites). This global reference time mostly means one which is provided by a GNSS (Global Navigation Satellite System) service, such as GPS. In these systems, it is the master clock which is responsible for attaining (e.g. via a GNSS receiver) and keeping the global reference time. It can then pass it on in the local communication network, usually using IEEE 1588 (Precision Time Protocol). It follows, that thus, the characteristics of such systems are heavily limited by the precision, accuracy and reliability of the used GNSS receiver. Our paper thus is about the examination of potentially promising GNSS receivers for which we developed a custom measurement system. This includes the design of a test PCB, the writing of a PC data collecting program, the formulation of MATLAB scripts which process the collected data, and the validation of the data collecting system via GNSS receivers simulated by TI evaluation boards. We also conducted measurements with the system on the Quectel L86 GNSS receiver, the results of which are presented in the paper.

This document defines a YANG data model for the configuration of IEEE 1588-2008 devices and clocks, and also retrieval of the configuration information, data set and running states of IEEE 1588-2008 clocks. The YANG module in this document conforms to the Network Management Datastore Architecture (NMDA).

This paper proposes a novel design for distribution system monitoring using a Modified Smart Meter (MSM) to enable accurate, time-synchronised measurements. The detailed design and the operation of the MSM are explained in this paper. The Precision Time Protocol (PTP), IEEE 1588, provides the main feature of time synchronisation in the MSM. The MSM uses the existing smart meter sensor hardware for collecting data measurements. This technique is expected to reduce the overall cost of MSM based distribution network monitoring implementation compared to the system based on Phasor Measurement Unit (PMUs). Some applications of the proposed MSM are outlined, and the applicability of the MSM is tested by simulating three-phase state estimation using standard IEEE networks and comparing its performance to standard PMU devices. The results indicate that the MSM could represent a viable monitoring solution for MV and LV distribution networks, providing an acceptable trade-off between performance and cost.

Timing over fiber achieves an accuracy at the subns level. We describe here the distribution over fiber implemented for industrial and scientific users, using two of the most common techniques, related to the IEEE-1588 standard, over different links spanning from 140 to 1700 km, and their performance.

A trans-national optical fiber time transfer link, based on the White Rabbit Precision Time Protocol has between established between the UTC timescale realizations of the Belgian Metrology Service (SMD) in Brussels, Belgium and the ESTEC Radio Navigation Laboratory in Noordwijk, The Netherlands. The link consists of a single fiber covering a span of approximately 260 km. For verification, the optical fiber time transfer is compared with GPS-based common view time transfer. The results of the two techniques agree well within the combined uncertainties. The estimated uncertainty for the optical fiber time transfer is 0.2 ns.

With the increasing deployment of large-scale distributed sensors and associated networks in the industrial IoT systems, highly reliable and precise clock synchronization gains ever increasing importance to ensure timeliness of the exchanged datagrams. While GPS (Global Position System), PTP (Precision Time Protocol) and NTP (Network Time Protocol) are prominent synchronization schemes, there are disadvantages in terms of accuracy achieved, hardware required, scalability, cost and associated failure modes. There is a need of robust, cost effective, scalable, easy to deploy, maintain and yet accurate synchronization method especially for IoT systems. This work focuses on implementation and validation of synchronization scheme using Kalman filter for IoT applications. The algorithm was implemented on a industrial platform for validation. The performance was assessed for its suitability in IoT based robust synchronization systems. The results show that the proposed approach and implementation is a promising candidate for synchronization in current and future IoT applications. The proof of concept confirms the feasibility of software only synchronization systems for IoT.

IEEE International Conference on Industrial Cyber Physical Systems (ICPS) (2019. Taipei, Taiwan), The implementation of 5G networks has several technological challenges, which are mainly related to the UltraReliable and Low Latency Communications (URLLC). One of these challenges is precise time transfer. Precision Time Protocol (PTP) is the most widely used protocol for precise time transfer. However, PTP performance may not be sufficient in large 5G networks.In this paper, we propose the use of white rabbit as the main technology for frequency and time transfer in 5G transport networks. However, white rabbit can only be implemented in wired links, thus the time transfer performance in wireless links may not be enough for the most challenging URLLC use cases. Therefore, we propose in this paper a modification of the white rabbit protocol that can be used in wireless communications. The proposed wireless white rabbit protocol has been tested by simulations over a single carrier point to point communication system, and different channel models. The results show significant improvements of the time transfer accuracy in Line Of Sight channels compared to other common wireless time transfer approaches and a similar performance to white rabbit over wired links., This work has been partly supported by DETRED (ELKARTEK 2017) project of the Basque Government (Spain) and by ARTEINE (TEC2017-86619-R) project of the Spanish Ministry of Economy and Competitiveness.

Clock synchronization procedures are mandatory in most physical experiments where event fragments are readout by spatially dislocated sensors and must be glued together to reconstruct key parameters (e.g. energy, interaction vertex etc.) of the process under investigation. These distributed data readout topologies rely on an accurate time information available at the frontend, where raw data are acquired and tagged with a precise timestamp prior to data buffering and central data collecting. This makes the network complexity and latency, between frontend and backend electronics, negligible within upper bounds imposed by the frontend data buffer capability. The proposed research work describes an FPGA implementation of IEEE 1588 Precision Time Protocol (PTP) that exploits the CERN Timing, Trigger and Control (TTC) system as a multicast messaging physical and data link layer. The hardware implementation extends the clock synchronization to the nanoseconds range, overcoming the typical accuracy limitations inferred by computers Ethernet based Local Area Network (LAN). Establishing a reliable communication between master and timing receiver nodes is essential in a message-based synchronization system. In the backend electronics, the serial data streams synchronization with the global clock domain is guaranteed by an hardware-based finite state machine that scans the bit period using a variable delay chain and finds the optimal sampling point. The validity of the proposed timing system has been proved in point-to-point data links as well as in star topology configurations over standard CAT-5e cables. The results achieved together with weaknesses and possible improvements are hereby detailed., Comment: 8 pages, 14 figures, proceedings of 21st IEEE Real Time Conference Colonial Williamsburg 9-15 June 2018

In systems with multiple radiation detectors, time synchronization of the data collected from different detectors is essential to reconstruct multidetector events such as scattering and coincidences. In cases where the number of detectors exceeds the readout channels in a single data acquisition electronics module, multiple modules have to be synchronized, which is traditionally accomplished by distributing clocks and triggers via dedicated connections. To eliminate this added cabling complexity in the case of a new radioactive gas detection system prototype under development at the French Atomic Energy Commission, we implemented time synchronization between multiple XIA Pixie-Net detector readout modules through the existing Ethernet network, based on the IEEE 1588 precision time protocol. The detector system is dedicated to the measurement of radioactive gases at low activity and consists of eight large silicon pixels and two NaI(Tl) detectors, instrumented with a total of three 4-channel Pixie-Net modules. Detecting NaI(Tl)/silicon coincidences will make it possible to identify each radioisotope present in the sample. To allow these identifications at low activities, the Pixie-Net modules must be synchronized to a precision well below the targeted coincidence window of 500–1000 ns. Being equipped with an Ethernet physical layer compatible with IEEE 1588 and synchronous Ethernet that outputs a locally generated but system-wide synchronized clock, the Pixie-Net can operate its analog-to-digital converters and digital processing circuitry with that clock and match time stamps for captured data across the three modules. Depending on the network configuration and synchronization method, the implementation is capable to achieve timing precisions between 300 ns and 200 ps.

A uniform time system for different intelligent electronic devices (IEDs) has a great significance for power system operation, monitoring, control, and fault analysis in smart substations. In this chapter, different kinds of clock sources and common time synchronization principles are introduced, and IEEE 1588 precision time protocol (PTP), including time synchronization method considering transmission delay or not, is described in detail. Furthermore, IEEE 1588 synchronization application in circuit breaker management (CBM) IED and sampling value synchronization technology are illustrated with actual project cases. Finally, synchronization test technology used in different applications is discussed.

Clock synchronization protocols such as the precision time protocol (PTP), which are used to synchronize components of distributed systems, are fundamental to enable timed and coordinated activities, e.g., in real-time applications within the industrial Internet of things (IIoT). In theory, PTP is able to achieve a precision on the order of nanoseconds. However, its practical accuracy remains limited by packet delay variations. In this paper, we hence present a novel approach to increase the synchronization precision of PTP. Our approach (PTP-LP) relies on PTP to obtain precise hardware timestamps taken during multiple synchronization periods. These timestamps establish the constraints for a Linear Programming (LP) solver that is used to estimate the clock differences between devices. Moreover, we propose the heuristic PTP-H that achieves comparable accuracy but is less computationally complex. We evaluate PTP-LP and PTP-H in comparison with two state-of-the-art approaches under various conditions in terms of clock stabilities and packet delay distributions. PTP-LP and PTP-H are fully compatible with existing standards and show to be in particular robust to varying packet delays. Especially, PTP-LP outperforms previous approaches in presence of a stable hardware clock and unknown non-negligible network delay, which are both realistic working conditions.

In this paper, an extension of Precision Time Protocol (PTP) to enable energy-efficient clock synchronization between the nodes within Wireless Sensor Network (WSN) is proposed. PTP is nanosecond accuracy clock synchronization protocol in which nodes are organized in master-slave hierarchy on the basis of clock accuracy by means of Best Master Clock (BMC) algorithm. The algorithm considers clock accuracy to select best clock in the system. A novel modification of IEEE 1588 BMC algorithm for energy-constraint multi-hop WSN has been proposed to reduce clock convergence time and energy needed by considering out-degree of clocks without sacrificing synchronization accuracy. The new algorithm results in energy efficient clock synchronization that makes it most appropriate for low-power multi-hop wireless sensor networks. We present NS-3 simulation data that confirms the effectiveness of work.

IEEE 1588 is a recently developed protocol for clock synchronization in a wired network with micro-second precision. Clock synchronization is usually a challenge in industrial real time applications such as robotics, industrial controls, smart power grids and Telecommunications. In this paper, we have implemented the IEEE 1588 Precision Time Protocol on a compact Raspberry Pi based Embedded System. We have analyzed the performance of the Precision Time Protocol over both wireless local area network and wired networks under real time conditions. Also, we have made a comparison of the synchronization performance over two communication media, guided and unguided with variable path losses. Through this study, we can evaluate the performance of Precision Time Protocol for different applications and determine the best possible operating parameters for different deployment scenario.

Accurate timestamping with 1 µs precision is required by power system monitoring and control equipment, including: Phase Measurement Units (PMUs) for real-time measurement and control; travelling wave detectors for fault location, protection and control; and sample value measurement techniques associated with the IEC 61850 process bus. The conventional way of achieving this is to transmit 1-PPS or IRIG-B timing signals using dedicated cables but such an approach is expensive and difficult to update as secondary control systems evolve. IEEE 1588 precision time protocol (PTP) allows the transmission of time information with sub-microsecond accuracy in an Ethernet network. However, a comprehensive study is required to enhance the confidence of the power industry in using PTP in present and future IEC 61850 based substations. This paper delivers a design and experimental validation of the real-time time synchronisation characteristics achievable with IEEE 1588. Several factors which can potentially affect the synchronisation accuracy in delivering a time reference from the master clocks to the end devices during both steady-state and transient changes were investigated. The objective is to increase the understanding of the real-time performance of a complete IEEE 1588 timing system applied in transmission substations, and identify the limitations of commercially-available devices.

Fine-grain time synchronization is important to address several challenges in today and future High Performance Computing (HPC) centers. Among the many, (i) co-scheduling techniques in parallel applications with sensitive bulk synchronous workloads, (ii) performance analysis tools and (iii) autotuning strategies that want to exploit State-of-the-Art (SoA) high resolution monitoring systems, are three examples where synchronization of few microseconds is required. Previous works report custom solutions to reach this performance without incurring in extra cost of dedicated hardware. On the other hand, the benefits to use robust standards which are widely supported by the community, such as Network Time Protocol (NTP) and Precision Time Protocol (PTP), are evident. With today's software and hardware improvements of these two protocols and off-the-shelf integration in SoA HPC servers no expensive extra hardware is required anymore, but an evaluation of their performance in supercomputing clusters is needed. Our results show NTP can reach on computing nodes an accuracy of 2.6us and a precision below 2.7us, with negligible overhead. These values can be bounded below microseconds, with PTP and low-cost switches (no needs of GPS antenna). Both protocols are also suitable for data time-stamping in SoA HPC monitoring infrastructures. We validate their performance with two real use-cases, and quantify scalability and CPU overhead. Finally, we report software settings and low-cost network configuration to reach these high precision synchronization results., ACM International Conference Proceeding Series, ANDARE '18 Proceedings of the 2nd Workshop on AutotuniNg and aDaptivity AppRoaches for Energy efficient HPC Systems

In this paper, a proposed hardware architecture implementation of more accuracy Precision Time Protocol (PTP) is presented. This approached design can be integrated into the wireless communication system for factory automation (FA) devices. In order to increase the closeness of the PTP harmony, we propose two approaches to improve the accurate synchronization to the nanosecond level by reducing the effects of asymmetric path delays of transmissions between master (MS) and slave (SL). The first one is the PTP protocol implementation at PHY layer to remove the random transmission jitters caused by higher layers. The second one is the full hardware implementation to remove the imbalanced timing made by the uneven hardware designs between MS and SL. Besides, a low overhead 3-frames exchange PTP approach to increase throughput of the transmission system is presented. We also implement successfully the PTP hardware design architecture and the SoPC of PHY-MAC and PTP integration system.

In the context of the IEEE 1588 Precision Time Protocol (PTP), estimating the delay's bias is a problem that appears in both one-way (using transparent devices) or two-way message exchange mechanisms. For estimating the offset via the two-way message exchange mechanism, it is usually assumed that the expected value of delays in forward and reverse directions are equal. However, this is not a realistic assumption for packet-based wide area networks, where delays in down-link and up-link directions may have a significant difference. In this work, we propose a solution to estimate the random delay's bias and improve the synchronization accuracy of IEEE 1588. Our method is easy to implement and is compatible with the current version of the protocol. We compared our results to no bias correction and the Boot-strap method. In addition to the improvement in synchronization accuracy, our method allows us to update the slave clock recursively. The proposed method works well even in the presence of large frequency offsets and can also be implemented by using different filters.

We introduce REVERSEPTP, a clock synchronization scheme for software-defined networks SDNs. REVERSEPTPi¾?is based on the Precision Time Protocol PTP, but is conceptually reversed; in REVERSEPTP, all nodes switches in the network distribute timing information to a single software-based central node the SDN controller, which tracks the state of all the clocks in the network. Hence, all computations and bookkeeping are performed by the central node, whereas the 'dumb' switches are only required to periodically send it their current time. In accordance with the SDN paradigm, the 'brain' is implemented in software, making REVERSEPTP flexible and programmable from an SDN programmer's perspective. We present the REVERSEPTPi¾?architecture and discuss how it can be used in typical SDN architectures. Our experimental evaluation of a network with 34 REVERSEPTP-enabled nodes demonstrates the effectiveness and scalability of using REVERSEPTP. Copyright © 2016 John Wiley & Sons, Ltd.

Channel based clock synchronization in packet switched networks (PSNs) is considered for, but not limited to, the time and safety/security critical application of power system protection. The synchronization accuracy requirement of power system protection devices used for line current differential protection is $$10\,\upmu $$10μs, which could be achieved in time division multiplexing networks that were traditionally used in that domain. In PSN, highly accurate synchronization can be achieved with the standard synchronization method IEEE 1588-2008 Precision Time Protocol (PTP) when devices in the communication network are equipped with so called boundary clocks (BCs) or transparent clocks (TCs). However, when BCs or TCs are not available, the required accuracy can hardly be achieved. In this work, a modification of the PTP is proposed that replaces the clock parameter estimation and the computation of the clock control signal. Thereby, the statistics of measured packet delays are considered to select optimum estimation schemes. It is shown that the here proposed method outperforms the Linux PTP in terms of timing accuracy by a factor of 2 in enterprise local area networks and by a factor of 10 in Carrier Ethernet wide area networks.

The application of White Rabbit precision time protocol (WR-PTP) in long-distance optical fiber links has been investigated. WR-PTP is an implementation of PTP in synchronous Ethernet optical fiber networks, originally intended for synchronization of equipment within a range of 10 km. This paper discusses the results and limitations of two implementations of WR-PTP in the existing communication fiber networks. A 950-km WR-PTP link was realized using unidirectional paths in a fiber pair between Espoo and Kajaani, Finland. The time transfer on this link was compared (after initial calibration) against a clock comparison by GPS precise point positioning (PPP). The agreement between the two methods remained within ${\pm }{2}\; \text{ns}$ over three months of measurements. Another WR-PTP implementation was realized between Delft and Amsterdam, the Netherlands, by cascading two links of 137 km each. In this case, the WR links were realized as bidirectional paths in single fibers. The measured time offset between the starting and end points of the link was within 5 ns with an uncertainty of 8 ns, mainly due to the estimated delay asymmetry caused by chromatic dispersion.

This paper proposes a distributed nodes-based clock synchronization method to sustain sub-microsecond precision synchronization of slave clocks upon master clock failure in IEEE 1588 PTP (precision time protocol) system. The sustaining is achieved by synchronizing the slave clocks to the estimated reference clock which is obtained from the analysis of distributed slave clocks. The proposed method consists of two clock correction functions (i.e., a self-correction and a collaborative correction, respectively). Upon master failure, the self-correction estimates a clock correction value based on the clock model which is constructed during normal PTP operation. The collaborative correction is performed in the preselected management node. The management node estimates a reference clock by collecting and analyzing clock information gathered from the other slave clocks. The performance of the proposed method is simulated by computer to show its usefulness. It is confirmed that the fifty (50) clock model-based collaborative correction maintains 10−6 second PTP accuracy for 10 min prolonged period after the master failure when tested with clock offset variations less than 50 ppm.

The local controller of an AC/DC converter for ITER coil power supply comprises a conventional system, an interlock system, and a safety system, which exhibit high reliability and availability through optimized designs for each system feature. The conventional system is made of three controllers according to each function, such as an interface controller (INTFC), an alpha controller (ALPC), and an analog-to-digital converting controller (ADC). They are configured with a 1 kHz UDP for real-time communication and 10 Hz TCP for transient recorder and with the digital fault recorder function to help facilitate data analysis and to easily troubleshoot problems in the fault event to improve the availability. Further, it is designed for accurate diagnosis by delivering time-stamped data to the parent system using the precision time protocol following the specification of IEEE 1588-2008 v2. The interlock system comprises a slow/fast local interlock controller (S-LIC/F-LIC). The S-LIC is configured with a redundant power supply and redundant Profinet communications for system availability, as well as a highly reliable programmable logic controller (PLC) for system reliability. The F-LIC is designed with an analog circuit board for protection and is evaluated for reliability. The safety system comprises highly reliable PLCs with a redundant power supply to monitor the safety-relevant signals and to transmit them to the parent system for occupational safety. In this study, the local controller of an AC/DC converter is introduced with designs applied to each system to satisfy the requirement and improve its reliability and availability.

Emerging technologies such as Fog Computing and Industrial Internet-of-Things have identified the IEEE 802.1Q amendment for Time-Sensitive Networking (TSN) as the standard for time-predictable networking. TSN is based on the IEEE 1588-2008 Precision Time Protocol (PTP) to provide a global notion of time over the local area network. Commonly, off-the-shelf systems implement the PTP in software where it has been shown to achieve microsecond accuracy. In the context of Fog Computing, it is hypothesized that future industrial systems will be equipped with FPGAs. Leveraging their inherent flexibility, the required PTP mechanisms can be implemented with minimal hardware usage and can achieve comparable synchronization results without the need for a PTP-capable transceiver. This paper investigates the practical challenges of implementing the PTP and proposes a hardware architecture that combines hardware-based time-stamping with a rate adjustable clock design. The proposed architecture is integrated with the Patmos processor and evaluated on an experimental setup composed of two FPGA boards communicating through a commercial-off-the-shelf switch. The proposed implementation achieves sub-microsecond clock synchronization with a worst-case offset of 138 ns.

Wide Area Monitoring Protection and Control (WAMPAC) systems play an increasingly important role in electric power system. They allow the measurement and the analysis of real time data to improve power system‘s reliability and efficiency. To work properly, every element of a WAMPAC system must be synchronized to a common reference time. Currently, the most common synchronization source is GPS, a system greatly vulnerable to cyber-attacks. To fully exploit WAMPAC systems‘ potential, cyber security issues must be taken into account. One possible solution could be the utilization of Precision Time Protocol (PTP) over Ethernet, as an alternative synchronization source.

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 (WR) is a widely used implementation to create high accuracy time dissemination networks. On-site network calibration can be avoided when using absolute calibrated components, which can be freely exchanged without recalibration. Absolute calibration of high accuracy time dissemination network components enables independent developers and/or vendors to exchange their calibrated components while achieving absolute sub ns timing. Absolute calibration enforces standardization.This paper presents procedures and methods for absolute calibration of time dissemination networks, in particular WR.

In this paper, we analyze the estimation capabilities of IEEE 1588-2008 Precision Time Protocol (PTP) and propose a super-imposed clock timing aware signal exchange protocol over PTP. The proposed protocol, without impacting any existing PTP infrastructure, provides independent clock parameter estimates. In addition, it also provides relative clock phase offset which is not detectable through standard PTP. We demonstrate how the supplementary estimates from the proposed method can be used to improve overall clock synchronization accuracy and also discuss the use of clock phase information in improving PTP event timestamp resolution.

A new revision of IEEE 1588 Precision Time Protocol is currently being developed, which will include revised specifications regarding security. The security mechanism consists of two verification approaches, immediate and delayed; we implemented both approaches on top of PTPd, an existing open source implementation of PTP. We support the immediate verification security approach using manual key management at startup, and we support the delayed verification security approach emulating automated key management for a set of security parameters corresponding to one manually configured time period. In our experiments, we found that added performance cost for both verification approaches was within 25 µs, and PTP synchronization quality remained intact when security was enabled.

Security on Internet communications has become an essential value in most of the modern IT infrastructures. An increasing number of organizations are improving their security mechanisms, looking for better protection against cyber attacks. Particularly, security has a principal role on the deployment and design of embedded and distributed systems as Cyber-Physical Systems (CPS) for the Industrial Internet of Things (IIoT).In this paper we present a simple solution to improve the security in Ethernet communications based on time transfer capabilities available in CPS. A hardware assisted implementation of a Time Varying Encryption System (TVES) has been developed, in which the current time is used as an input for a periodic time dependant key generation, making more difficult to access the transmitted or received data. Using the currently widely adopted Precision Time Protocol (PTP) for time distribution with hardware assisted timestamping, a sub-microsecond synchronization level has been achieved. This accuracy level allows a time varying encrypted communication scheme between master and slave based on a shared time reference.In our experiments, a symmetric-key scheme is used, but the method is fully compatible with asymmetric-keys scenarios. Due to the time dependancy of the keys, in case of a malicious access to the retrieved data, a brute-force decryption will not be useful because of the wide range of generated keys and their refresh rate. This range will result on an external perception of a random encryption.

Modern automotive control applications require a holistic time-sensitive development. Nowadays, this is achieved by technologies specifically designed for the automotive domain, like FlexRay, which offer a fault-tolerant time synchronization mechanism built into the protocol. Currently, the automotive industry adopts the Ethernet within the car, not only for embedding consumer electronics, but also as a fast and reliable backbone for control applications. Still, low-cost but highly reliable sensors connected over the traditional Controller Area Network (CAN) deliver data needed for autonomous driving. To fusion the data efficiently among all, a common timebase is required. The alternative would be oversampling, which uses more time and energy, e.g., at least double the perception rates of sensors. Ethernet and CAN do require the latter by default. Hence, a global synchronization mechanism eases tremendously the design of a low power automotive network and is the foundation of a transparent global clock. In this article, we present the first step: Synchronizing legacy FlexRay networks to the upcoming Ethernet backbone, which will contain a precise clock over the generalized Precision Time Protocol (gPTP) defined in IEEE 802.1AS. FlexRay then could still drive its strengths with deterministic transmission behavior and possibly also serve as a redundant technology for fail-operational system design.

This paper addresses the problem of robust clock phase offset estimation for the IEEE 1588 precision time protocol in the presence of unknown asymmetric path delays in electrical grid networks. Assuming the availability of multiple master-slave communication paths, new lower bounds on the mean square estimation error for this problem were recently derived by the authors. In this paper, we present a novel phase offset estimation scheme that uses robust M-estimators for identifying the asymmetric master-slave communication paths. After discarding observations from the paths identified as asymmetric, we employ the computationally efficient L-estimators, which are linear combinations of order statistics, to estimate the phase offset from the symmetric master-slave communication paths. Simulation results show that the proposed phase offset estimation scheme exhibits performance close to the lower bounds in different network scenarios.

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 our previous work, we used the Precision Time Protocol (PTP) to measure one-way delay and to quantify packet loss ratios, and we proposed PTPmesh as a cloud network monitoring tool. In this work, we provide a better understanding on how to exploit the measurement data offered by PTPmesh and present a detailed analysis of PTPmesh measurements collected in ten data centers from three cloud providers. Our findings reveal different latency, latency variance and packet loss characteristics across data centers. Through our analysis, we showcase the strengths and limitations of PTPmesh as a cloud network monitoring tool. To foster further research in this area, we make our dataset available.

In this paper we present a fundamentally redesigned Global Navigational Satellite System (GNSS) receiver to master clock interface based on our previous design for IEEE 1588 Precision Time Protocol (PTP) master clocks. The new design is optimized for modern timing GNSS receivers; including GPS, Galileo, and GLONASS GNSS; which provide better timing accuracy and precision than previous generic navigational or even older timing GPS receivers. The new design is required because new timing GNSS receivers have lower than 10 ns error while the errors introduced by the previous interface solution is one or two magnitudes bigger than that, causing degraded system wide timing performance for new systems. Better performance is achieved by an error source analysis and a delicate component selection based on the results of the analysis, and in addition, timing oriented PCB routing. Furthermore, the new design is more compact, integrated with a CPU board, and therefore, ready to be deployed in prototype applications. The paper also provides an initial performance evaluation of the improved reference clock interface.

IEEE 1588 defines a precision time protocol, which is widely used in distributed test and measurement systems. It is very important to capture the timestamps of the location that can affect the synchronization accuracy seriously in the synchronization process. In this paper, we proposed a method to capture the timestamps based on specialized hardware Field Programmable Gate Array (FPGA) between the physical layer and MAC layer. We designed IEEE 1588 message detection module and frequency compensation clock to detect IEEE 1588 message and record the timestamps, respectively. This method can eliminate the delay jitter which is caused by the network protocol stack to improve the synchronization accuracy. The test experiments results show that 97.76% of the synchronization deviation is located within ±40nS.

IEEE 1588 specifically describes the Precision Time Protocol (PTP) for clock synchronization across multiple domains. The PTP implementations have a large design space because of the range of possibilities in the delay mechanism, types of clocks and topological variations. Time synchronization is considered as a challenge for real time applications such as smart grids, Internet of Things and Telecommunications etc. Multiple algorithms have been proposed to perform synchronization in which the IEEE 1588 standard defines the most reliable synchronization protocol while providing up to sub-microsecond time precision. In this paper, we have made a comparison of IEEE 1588 and IEEE 802.15.4 standards to get a sensible decision of the synchronization protocol for real time applications. Also, we have modified the existing LibPTP library to analyze the real time network traffic that can influence the synchronization process. Through simulation based studies, we have been able to analyze the performance of IEEE 1588 protocol in a constrained network.

In this paper, an enhanced precision time protocol (PTP) to enable precise clock synchronization between the nodes within an industrial wireless sensor network deployed for critical control and automation applications is proposed. As it will be shown, by incorporating clock drift factor, the accuracy of clock offset estimation of conventional PTP scheme can be significantly improved. Furthermore, in order to enhance the application of proposed clock synchronization scheme, typically in non-line-of-sight industrial communication environment, the problem of efficient symbol timing synchronization is also studied, and a simplified, yet efficient, start of the frame detector that enables robust timestamp message decoding during clock synchronization period is also proposed.

The synchronization accuracy achieved via the IEEE 1588 Precision Time Protocol (PTP) in packet-based fronthaul networks is substantially impaired by packet delay variation (PDV). Nevertheless, in the particular case of deployment over tree topologies, it is known that PDV can be avoided by controlling the departure of PTP packets such that they experience close to constant delays over the fronthaul. This paper analyzes controlled PTP departure under constraints that are peculiar to a fronthaul scenario of interest and considering that radio traffic itself behaves as background traffic relative to PTP. Since the method involves buffering of radio traffic prior to controlled PTP transmissions, its impact on buffer sizes at the baseband and radio units, and the corresponding increase in fronthaul latency are also analyzed. In the end, results collected through a self-developed FPGA-based testbed are presented. This work was supported in part by the Innovation Center, Ericsson Telecomunicac¸ ˜oes S.A., Brazil, CNPq/Capes, Brazil, and by the European Union through the H2020 collaborative Europe/Taiwan research project 5G-CORAL (grant agreement no. 761586).

Large experiments for studying high energy physics phenomena are requiring accurate time synchronization. The wide area occupied by such kind of facilities challenges the achievable accuracy using traditional time distribution systems. At CERN, the White Rabbit (WR) project extended the Precision Time Protocol (PTP) in order to provide sub-nanosecond accuracy with standard deviation less than 50 ps. As a matter of fact, the WR systems relies also on the frequency syntonization of the L1 frontend to limit the local clock synchronization uncertainty. In particular, this work is focused only on the contribution related to the jitter of the Network Layer 1 (L1) (1 Gbps fiber optic transceiver) to the overall uncertainty. An experimental setup is proposed and the real implementation of the WR system is tested. The results show that under steady conditions the impact of the fiber optic transceiver on the overall jitter transfer is restricted to less than 0.3 ps RMS, practically negligible with respect to other uncertainty contributions of the whole system.

Synchronization is an essential prerequisite for all wired and wireless networks to operate. It is fundamental requirement for data integrity, and without it data will be affected by errors and networks will have outages. The IEEE 1588 Precision Time Protocol (PTP) enables precise synchronization of clocks via packet networks with accuracy down to the nanoseconds range. PTP-based solution can be used in various heterogeneous systems like industrial automation, RADAR, Telecom networks. FPGA-based implementation of PTP eliminates Ethernet latency and jitter issues through hardware Timestamping. It gives precise and accurate synchronization in comparison with Operating System-based Timestamping solutions. Accuracy in the range of 10–100 ns is achievable using FPGA-based platform. This paper explains basic mechanism of PTP protocol and advantages of FPGA-based platform for its implementation. It provides detail implementation of PTP on FPGA platform, design flow, testing methodology and its results.

An Opnet model of a time-aware shaper (TAS) based on the IEEE 802.1Qbv standard is presented. The TAS model is assumed to be the scheduling entity in an Ethernet-based fronthaul network, comprising of Ethernet switches. The fronthaul transports different traffic flow types as envisioned in next generation Radio Access Networks (RANs), including those for a timing protocol (based on the precision time protocol) and those from the implementation of different RAN functional subdivisions. The performance of the TAS is compared to that of a strict priority regime and is quantified through the frame delay variation of the high priority traffic when this contends with lower priority traffic. The results show that with the TAS implementation, contention effects can be overcome and frame delay variation (frame jitter) can be removed. Timing instability in the significant events of the scheduler is considered and a solution to overcome this issue is proposed.

A Dante network card and development template developed by Audinate were used as a platform for realizing an Ethernet synchronous audio playback system. A personal computer (PC) was connected to each Dante device through a switch hub and Ethernet cable PC to transmit sound before TAS3204EVM was applied in digital signal processing and EQ adjustment for application in a live music concert. The expensive wire and cable currently used in live music concerts can be replaced with an Ethernet cable, substantially reducing costs. To ensure that the Dante devices deliver sound simultaneously, an artificial delay was introduced to enable devices closer to the sound source to delay the playback time while devices farther from the sound source play back sound with the other devices. This study examined how the IEEE 1588 Precision Time Protocol can be used for clock correction to synchronize the sound of all devices. Zero Configuration Networking (ZCN) was used to enable the devices to obtain an Internet Protocol address, and the Multicast Domain Name System was employed to obtain the device names, thus ensuring that User Datagram Protocol control instructions can be correctly delivered to control interdevice channel connections.

This paper examines synchronization of computer clocks connected via a data network and proposes a skewless algorithm to synchronize them. Unlike existing solutions, which either estimate and compensate the frequency difference (skew) among clocks or introduce offset corrections that can generate jitter and possibly even backward jumps, our solution achieves synchronization without these problems. We first analyze the convergence property of the algorithm and provide explicit necessary and sufficient conditions on the parameters to guarantee synchronization. We then study the effect of noisy measurements (jitter) and frequency drift (wander) on the offsets and synchronization frequency, and further optimize the parameter values to minimize their variance. Our study reveals a few insights, for example, we show that our algorithm can converge even in the presence of timing loops and noise, provided that there is a well defined leader. This marks a clear contrast with current standards such as NTP and PTP, where timing loops are specifically avoided. Furthermore, timing loops can even be beneficial in our scheme as it is demonstrated that highly connected subnetworks can collectively outperform individual clients when the time source has large jitter. The results are supported by experiments running on a cluster of IBM BladeCenter servers with Linux., Comment: to appear in ToN. arXiv admin note: substantial text overlap with arXiv:1208.5703

The Schenberg gravitational wave (GW) detector has been under development for the past few years. A scientific run is planned for the near future. The main technique used to confirm a GW is the search for time coincident events between multiple detectors. Therefore, a reliable timestamp is essential for events found in data from each detector. In the particular case of the Schenberg detector, we are planning a low latency analysis, which requires that no data sample be lost during either data acquisition (DAQ) or transmission, and that time correction be done online. The aim is to provide reliable data where each sample carries its own timestamp information. GW event candidates are pointed out after a dedicated analysis and their time of occurrence are determined by these samples. We present here the DAQ solution developed for the Schenberg detector. It is easy to implement this solution using equipment commonly found in most laboratories. No specific equipment using precision time protocol or other protocol was needed to synchronize the sampling. In addition, no transmission time is needed to be explicitly known. The timing precision is limited only by the chosen sampling frequency, which fulfills the data analysis needs.