Showing papers on "Precision Time Protocol published in 2011"

Method and apparatus for synchronizing measurements taken by multiple metrology devices

Abstract: Apparatus includes at least two devices that communicate with each other, wherein a first one of the at least two devices having an IEEE 1588 precision time protocol interface, the interface including one or more components configured for communications in both a wired manner and a wireless manner with a second one of the at least two devices. The second one of the at least two devices having an IEEE 1588 precision time protocol interface, the interface including one or more components configured for communications in both a wired manner and a wireless manner with the first one of the at least two devices. Wherein one of the at least two devices includes a master clock and the other one of the at least two devices includes a slave clock, wherein the master clock communicates a time to the slave clock and the slave clock is responsive to the communicated time from the master clock to adjust a time of the slave clock if necessary to substantially correspond to the time of the master clock, thereby time synchronizing the at least two devices together.

Performance Analysis of Kalman-Filter-Based Clock Synchronization in IEEE 1588 Networks

Abstract: Performances in network-based synchronization depend on several related factors, including the instability of local clocks, the rate at which timing information is exchanged, and the accuracy of the resulting correction estimates. This paper analyzes these effects and their relationships, showing how these may affect the design of an IEEE 1588 Precision Time Protocol synchronization scheme. This paper introduces a state-variable clock model for which realistic parameters can be obtained for different kinds of clocks from experimental measurements of Allan variance plots. A Kalman-filter-based clock servo employing this model is developed, and a simulation analysis of the behavior of clock regulation and the effect of parameter variations on its performances is presented.

A software-only PTP synchronization for power system state estimation with PMUs

Abstract: Synchronized Phasor Measurement Units (PMUs) are becoming a key element of monitoring, protection, control and state estimation applications in power systems and are the basis for the implementation of Wide Area Monitoring Systems (WAMSs). This paper investigates the possibility of using a software-only PTP (Precision Time Protocol) synchronization method to synchronize different Phasor Measurement Units (PMUs) and how this synchronization impacts the State Estimation. In this context, as a case study, the output data of the PMUs have been used to estimate the state of a power system of reduced size and complexity. A laboratory experimental setup has been built to evaluate the performance achievable with the proposed synchronization solution. The results thus obtained and the performance analysis are discussed in this paper.

Towards high accuracy in IEEE 802.11 based clock synchronization using PTP

Abstract: The introduction of the precision time protocol has brought forth the possibility to have a standardised synchronization mechanism in networks, independent from the actual communication technology. However, it can be observed, for example in the annexes of the standard, that many implementations focus only on Ethernet based communication. The logical next step is to investigate how this protocol will fare when used for synchronizing clocks in a distributed manner over IEEE 802.11 based devices. The availability of features like roaming, the broadcast nature of the wireless medium and different hardware platform architectures require an investigation on how clock synchronization can be realized in wireless environments. This paper proposes an approach to import the precision time protocol to IEEE 802.11. Furthermore, standard nodes are enhanced with software timestamping, leading to a synchronization accuracy of a few microseconds.

Method for realizing sub-microsecond synchronization accuracy based on PTP (Precision Time Protocol)

Abstract: The invention relates to a method for realizing sub-microsecond synchronization accuracy based on a PTP (Precision Time Protocol), belonging to the technical field of communication; in order to obtain high-accuracy synchronization efficiency and save hardware investment cost, the method comprises the following steps: before a master time sends synchronization messages, synchronizing a clock and a clock source of an Ethernet transceiver; obtaining average path delay of links by a delay request information packet delay measuring mechanism or measuring a waiting delay information packet delay measuring mechanism; and performing asynchronous correction on the links so as to realize sub-microsecond synchronization accuracy. In the method, the DP83640 Ethernet transceiver is adopted, network message time stamp can be exactly obtained, the PTP protocol on an AT91RM9200 platform is realized, and sub-microsecond synchronization accuracy can be realized. Via test, the synchronization accuracy can be up to 100ns; and the whole system is low in cost, excellent in openness and expandability, and easy to implement.

Sub-nanosecond timing system design and development for lhaaso project*

Abstract: The Large High Altitude Air Shower Observatory (LHAASO) project is designed to trace galactic cosmic ray sources by approximately 10,000 different types of ground air shower detectors. Reconstruction of cosmic ray arrival directions requires a precision of synchronization down to sub-nanosecond, a novel design of the LHAASO timing system by means of packet-based frequency distribution and time synchronization over Ethernet is proposed. The White Rabbit Protocol (WR) is applied as the infrastructure of the timing system, which implements a distributed adaptive phase tracking technology based on Synchronous Ethernet to lock all local clocks, and a real time delay calibration method based on the Precision Time Protocol to keep all local time synchronized within a nanosecond. We also demonstrate the development and test status on prototype WR switches and nodes.

Test and evaluation system for multi-protocol sampled value protection schemes

Abstract: Proposed transmission smart grids will use a digital platform for the automation of substations operating at voltage levels of 110 kV and above. The IEC 61850 series of standards, released in parts over the last ten years, provide a specification for substation communications networks and systems. These standards, along with IEEE Std 1588-2008 Precision Time Protocol version 2 (PTPv2) for precision timing, are recommended by the both IEC Smart Grid Strategy Group and the NIST Framework and Roadmap for Smart Grid Interoperability Standards for substation automation. IEC 61850-8-1 and IEC 61850-9-2 provide an inter-operable solution to support multi-vendor digital process bus solutions, allowing for the removal of potentially lethal voltages and damaging currents from substation control rooms, a reduction in the amount of cabling required in substations, and facilitates the adoption of non-conventional instrument transformers (NCITs). IEC 61850, PTPv2 and Ethernet are three complementary protocol families that together define the future of sampled value digital process connections for smart substation automation. This paper describes a specific test and evaluation system that uses real time simulation, protection relays, PTPv2 time clocks and artificial network impairment that is being used to investigate technical impediments to the adoption of SV process bus systems by transmission utilities. Knowing the limits of a digital process bus, especially when sampled values and NCITs are included, will enable utilities to make informed decisions regarding the adoption of this technology.

System and method for accounting for time that a packet spends in transit through a transparent clock

Abstract: Despite a recent revision, IEEE 1588™-2008 does not provide a complete implementation for PTP (precision time protocol) that accounts for variable delays introduced by network components. According to a broad aspect, the present disclosure provides implementations that account for variable delays introduced by network components. Therefore, the amount of time that a packet spends in transit through a transparent clock can be accounted for. According to another broad aspect, there is provided a master-slave mode that allows a transparent clock to function as a master or a slave to another clock.

Synchronizing the Linux system time to a PTP hardware clock

Abstract: As computer and embedded systems are becoming more complex and distributed, keeping accurate time throughout the whole system becomes a challenging task. The IEEE 1588 Precision Time Protocol was designed to achieve very accurate synchronization in distributed environments. Linux is becoming the leading operating system for embedded devices, but little attention has been paid to the issue of how to internally synchronize the Linux system clock with the PTP hardware clock. Our paper presents the current status in this area, highlights possible solutions for this problem, and describes our efforts to address this key issue.

Transparent Clocks vs. Enterprise Ethernet switches

Abstract: Precision Time Protocol (PTP) is a high-precision time synchronization protocol designed to operate over a local area network. PTP, typically referred to as 1588, is defined by the IEEE Standard 1588™-2008 and provides clock synchronization at the nanosecond level. Even though devices with support for 1588 are widely available, there have been few performance studies of such devices. This paper investigates the impact of latency and high bandwidth background traffic on 1588 clock synchronization in a network consisting of both 1588 and non-1588 aware switches. As expected, we found that 1588-aware switches provide higher precision time synchronization in smaller-scale networks. In larger networks with congestion, 1588-aware switches were unable to maintain high accuracy clock synchronization due to the lack of traffic prioritization. Our results also show that having cut-through Enterprise Ethernet switches with prioritization enabled is adequate for maintaining sub-microsecond synchronization.

A clock state estimator for PTP time synchronization in harsh environmental conditions

Abstract: In industrial automation networks based on the Precision Time Protocol (PTP) large temperature changes as well as mechanical shocks and vibrations may severely affect the performance of the local oscillators clocking the network nodes, thus making accurate time synchronization challenging. This problem is particularly critical in large industrial networks with long linear paths, as multiple uncertainty sources tend to accumulate while PTP event messages are forwarded towards the slave clocks. In this paper, the performance of a clock state estimator based on a special Kalman filter as well as on a detailed model of the PTP communication mechanism is described. The reported simulation results when the network nodes are subject to changeable environmental conditions provide interesting guidelines to keep synchronization accuracy in industrial networks within given boundaries.

Interworking agent adapted to interact between network and precision time protocol entities

Abstract: The embodiments of the present invention refer to an interworking agent aimed at being installed in a network node comprising a Precision Time Protocol “PTP” module, said agent comprising: a synchronization-side interface configured to measure Precision Time Protocol “PTP” metrics for detecting a Precision Time Protocol “PTP” signal failure, read and modify Precision Time Protocol “PTP” parameters of the Precision Time Protocol “PTP” module, at least one network-side interface configured to measure network metrics for selecting the optimal path for packet synchronization signals monitor network events for detecting a network path change, read and modify signals exchanged with a network planning entity and, signals exchanged between network nodes at the network level in order to communicate with remote interworking agents located in other network nodes.

Distributed IEC 61499 material handling control based on time synchronization with IEEE 1588

Abstract: This paper proposes a method of time-driven control with high-precision synchronous clocks in distributed control systems built following the IEC 61499 standard. It investigates the impact of applying time-driven control on performance of material handling systems. A time-driven control system for a multi-diverter conveyor line has been developed using IEC 61499 Function Blocks architecture with support of the IEEE 1588 Precision Time Protocol. Analytic performance model has been developed and comparisons between the time-driven and two other possible control designs have been conducted and elaborated in terms of costs, logic design, and system throughput.

Synchrophasors measurement in a GPS-IEEE 1588 hybrid system

Abstract: This paper presents a study on a hybrid architecture considering Global Positioning System (GPS) and Precision Time Protocol (PTP), defined in Standard IEEE 1588, for applications in electric power systems, with reference to one of the most challenging measurement problems, namely the measurement of synchrophasors. The proposed approach refers in particular to situations in which many measurement devices, connected to each other by suitable communication links, are located in a geographically limited subarea of the power system. A laboratory experimental setup has been built to evaluate the performance achievable with this solution. A detailed analysis of the obtained results is presented. Copyright © 2010 John Wiley & Sons, Ltd.

Time synchronization method and device

Abstract: The invention discloses a time synchronization method and device which are applied to a PTP (precision time protocol) time synchronization network so as to shorten the time spent in switching the communication port states of each device and guarantee the stability of the PTP time synchronization network. The method comprises the following steps: receiving announce messages with GM (game master) identification information by a BC (boundary clock) device; when the GM identification information in announce messages of the elder generation at the present moment is determined to be different from the GM identification information in announce messages of the elder generation at the previous moment, controlling communication ports in a non-Master state at the present moment to switch to a Master state directly; and when the GM identification information carried by the announce messages of the elder generation at the present moment is determined to be same as the GM identification information carried by the announce messages of the elder generation at the previous moment, controlling the ports in the non-Master state to enter into a Pre-master state.

Preventing the Collision of Requests From Slave Clocks in the Precision Time Protocol (PTP)

Abstract: The Precision Time Protocol (PTP) distributes a time reference across a network. It specifically addresses demanding environments, where it can reach sub microsecond precision using appropriate technologies. Its scalability is primarily limited by packet delay variations induced by packet collisions. While it is possible to avoid collisions with non-PTP packets using traffic management technologies, collision between PTP packets is an open problem in large systems with critical clock precision requirements. We propose a coordination algorithm that avoids the occurrence of such collisions. It assumes that the master clock, which is the timing reference source, can send a packet in multicast to the slaves: this is not a restrictive hypothesis, since PTP itself takes advantage of this kind of connectivity, and it is also compatible with typical wireless environments. The algorithm operates without introducing additional traffic, it ensures an upper bound to the time between two successive synchronizations of any given slave, it does not alter the structure of the standard PTP messages, it envisions a dynamic number of slaves, it tolerates the replacement of the master with a hot spare in case of failure, and does not rely on specialized hardware. The algorithm has a footprint that does not insist on activities that are already time sensitive, and its operation is mostly concentrated on the master. The algorithm inherits security and fault tolerance limits from PTP: in particular this refers to malicious nodes, and to broken devices that may jam the network.

Architecture of an embedded time gateway between PTP and SNTP

Abstract: This paper deals with time synchronization in mixed network infrastructures for automation of industrial and electric plants, where old devices, which retrieve time information with the well-known NTP, must coexist with new IEEE1588 PTP compliant devices. Since PTP and NTP use very different time representations and synchronization strategies, an easy integration is quite difficult and requires additional hardware. The paper describes a transparent Time Gateway that is able to interface SNTP devices with a PTP synchronization domain (PTP devices and PTP switches). The Time Gateway has been realized with an embedded system based on an FPGA with a soft processor and an open source operating system. Preliminary experimental results show the feasibility of the proposed architecture, even if some improvements may be needed to match the time synchronization accuracy required by the legacy SNTP devices.

Impact of PMU sychronization on wide area state estimation

Abstract: This paper investigates the impact of the PTP (Precision Time Protocol) synchronization method, used to synchronize different Phasor Measurement Units (PMUs), on a state estimation application. As a case of study, the output data of the PMUs, synchronized by means of a software-only implementation of the PTP, have been used to estimate the state of an IEEE 57-bus power system.

Model-Based evaluation and improvement of PTP syntonisation accuracy in packet-switched backhaul networks for mobile applications

Abstract: Base stations in mobile networks have very strict frequency synchronisation (also referred to as syntonisation) requirements. As backhaul networks are migrated to asynchronous packet-switching technology, timing over packet using the IEEE 1588 Precision Time Protocol (PTP) replaces current synchronisation methods that rely on the synchronous bit clock of the network. With PTP, base-station clocks derive their frequency from the inter-packet delays of Sync messages sent by a high-quality time source at regular time intervals. Packet-delay variation (PDV) thus has a major impact on the achievable synchronisation quality, and the amount of PDV of a backhaul network determines whether the network can support frequency synchronisation of base stations. We present a simulation and an analytical approach to assessing the suitability of backhaul networks for clock synchronisation using PTP and derive two methods for reducing PDV.

The human positioning system based on the WiFi Direct and Precision Time Protocol

Abstract: under the harsh environment and special geological condition, the technology in the home market at present when used in the coal mine can't fulfill the need of the accurate positioning and tracking of the miner appropriately. For example, the RFID technology, which is popular in the most of Chinese colliery industry monitoring and location systems, just acts as an attendance system. The system can't exactly pinpoint the miners trapped in the underground when the accident happens. And WiFi location applied in the underground location also has its limitation that was born with the low precise accuracy. The CDMA indoor GPS system can work well in the underground environment, but it is too expensive for the large-scale popularization in the major coal mines. For the reasons of all of the above, we suggest that the developers and engineers should develop a system with the characteristics of good stability, high locating accuracy and low cost in the large-scale extension and so on. This is the purpose of the paper; we propose to combine the IEEE1588 Precision Timing Protocol (PTP) with WiFi Direct system. With the use of the Time of Arrival (TOA) measurement of distance algorithm, we can achieve the goal of wireless real-time location and miner tracking.

Time-complemented event-driven control framework for distributed motion control systems based on IEC 61499 and IEEE 1588

Abstract: This paper presents a preliminary study towards the applications of IEC 61499 Function Block standard in distributed motion control systems, where synchronization is of crucial importance. In particular, an investigation on the possibilities of applying event-driven function blocks in the time-based motion control system has been performed on the SIDEL SL90 packaging machine's control system. To achieve the required high-precision time synchronization and to provide the reference time, the IEEE 1588 Precision Time Protocol has been implemented in this work as the essential part of the packaging control system. A time-complemented event-based control framework has also been proposed.

Application of IEEE1588 time synchronization protocol in digital substation

Abstract: According to the time synchronization requirements of IEC61850 at different levels of digital substation,three synchronization modes are compared:hard-wired,SNTP(Simple Network Time Protocol) and IEEE1588 PTP(Precision Time Protocol).The clock types of IEEE1588 and their relationships are introduced and the principle of IEEE1588 PTP synchronization is analyzed in detail.The feasibility of IEEE1588 PTP synchronization with current hardware supporting conditions of digital substation is described.Two schemes of IEEE1588 PTP application in IEC61850-based substation for future substation automation systems are proposed:one for single substation and the other for multiple substations.In the proposed schemes,the redundant configuration of grandmaster clock using Beidou navigation satellite system,GPS(Global Positioning System) and atomic clock is discussed.

Time synchronization method for stacking system, stacking system and member equipment

Abstract: The invention provides a time synchronization method for a stacking system, the stacking system and member equipment. The stacking system participates in the general member (GM) election and synchronous spanning tree establishment of an external precision time protocol (PTP) network as logic equipment; and in the stacking system, a GM in the stacking system is determined according to the elected role of the stacking system in the external PTP network, a synchronous spanning tree is established in the stacking system by an internal notification message, and an internal synchronization message is transmitted on the internally established synchronous spanning tree to realize time synchronization in the stacking system. The invention realizes the precise time synchronization of the stacking system without influencing the time synchronization of other network equipment.

Use of IEEE 1588–2008 for a sampled value process bus in transmission substations

Abstract: IEC Technical Committee 57 (TC57) published a series of standards and technical reports for “Communication networks and systems for power utility automation” as the IEC 61850 series. Sampled value (SV) process buses allow for the removal of potentially lethal voltages and damaging currents inside substation control rooms and marshalling kiosks, reduce the amount of cabling required in substations, and facilitate the adoption of non-conventional instrument transformers. IEC 61850–9–2 provides an inter-operable solution to support multi-vendor process bus solutions. A time synchronisation system is required for a SV process bus, however the details are not defined in IEC 61850–9–2. IEEE Std 1588–2008, Precision Time Protocol version 2 (PTPv2), provides the greatest accuracy of network based time transfer systems, with timing errors of less than 100 ns achievable. PTPv2 is proposed by the IEC Smart Grid Strategy Group to synchronise IEC 61850 based substation automation systems. IEC 61850–9–2, PTPv2 and Ethernet are three complementary protocols that together define the future of sampled value digital process connections in substations. The suitability of PTPv2 for use with SV is evaluated, with preliminary results indicating that steady state performance is acceptable (jitter < 300 ns), and that extremely stable grandmaster oscillators are required to ensure SV timing requirements are met when recovering from loss of external synchronisation (such as GPS).

IEEE1588 time testing analyzer

Abstract: The utility model discloses an IEEE1588 time testing analyzer, which comprises an absolute clock system receiving module, an external clock signal receiving module, a clock signal input-output module, a clock signal processing module, a measurement analysis module, a main processing module and a display screen The clock signal processing module is respectively connected with the absolute clock system receiving module, the external clock signal receiving module, the measurement analysis module and the main processing module, and the measurement analysis module used for analyzing point-to-point measurement and measurement of other clock signals is respectively connected with the clock signal input-output module, the main processing module and the clock signal processing module The IEEE1588 time testing analyzer can be used as a fundamental testing and debugging tool for deploying, analyzing and developing IEEE1588 precision time protocol technology

An Approach of Time Measurement for Intelligent Components in Smart Substations

Abstract: As a high-precision time synchronization technology for distributed network,IEEE 1588 is very important for the construction of smart substations.Firstly,the principle of time synchronization of IEEE 1588,which gives the time synchronization process and the synchronization compensation algorithms of two link delay measurement mechanisms,is presented;then the time-related measurable contents during the synchronization of intelligent components,including the time synchronization accuracy of precision time protocol(PTP) utilizing intelligent components as master clock or slave clock,the sampling uniformity and output time of sampled value(SV) message and the response time and output time of generic object oriented substation event(GOOSE) message,are proposed;finally,the time-related parameters for the main transformer protection and monitoring intelligence component of UDT-531 are tested and analyzed.The results show that the measured time parameters of UDT-531 could basically meet the needs of IEC 61850 standard,thus the feasibility of the proposed time measurement approach is verified.

Examination of time and frequency control across wide area networks using IEEE-1588v2 unicast transmissions

Abstract: The IEEE 1588–2008 Precision Time Protocol (PTP) version 2 (IEEE 1588v2) can be used to synchronize a slave clock to a grandmaster clock over a wide area network (WAN). However, many of the algorithms the slaves use to steer to the master are optimized for a scenario where both devices are on the same subnet or local area network (LAN). This paper is a study of existing PTP hardware from a number of different manufacturers in unicast mode. We characterize the performance of the equipment, beginning with the timing outputs of the masters that are locked to their built-in Global Positioning System (GPS) receivers. Next, we compare the results of steering unicast clients to their masters through a LAN versus several wider-area network configurations such as virtual-LANs and the public Internet. Analysis of the results will show how clients of different manufacture handle the various network paths. It is our hope that these comparisons will instigate changes to clock steering and synchronization algorithms, which may help improve the overall capabilities of PTP for telecom and other networking environments. As network synchronization techniques improve, the quality of the PTP masters will become more significant. Therefore, the performance and calibration of PTP masters with respect to UTC(NIST) is also discussed.

Method and apparatus for extracting clock, and network communication equipment

Abstract: The embodiment of the present invention discloses a clock extraction method, device and network communications equipment. Each transmission port of the network communication equipment can receive at least two types of data streams, the at least two types include: Pseudo-Wire Emulation Edge-to-Edge (PWE3) and Precision Time Protocol IEEE 1588 over Ethernet. The method includes receiving data stream come from a first transmission port, and identifying the types of the data streams; performing clock extraction to the data stream according to the identification result, wherein, if the data streamtype is PWE3, performing PWE3 clock extraction to the data stream, and the data stream type is IEEE1588, performing IEEE1588 clock extraction to the data stream. The embodiment of the present invention supports a plurality of clock extraction modes for extracting clocks, thereby simplifying system design and reducing costs.

Multidevice Time Measurement System via a PTPD Network

Abstract: The precision time synchronization protocol daemon (PTPd) is a software package that realizes a PTP. In this paper, a traceable PTPd measurement system is examined. The key component of the proposed time measurement system is the PTPd. It runs in a Linux kernel-based network. The PTPd operation mode is free running. A stable clock (i.e., an embedded system oscillator in our experiments) plays the role of a master clock. Measured clocks (i.e., desktop system time in our experiments) play the roles of slave clocks. From our results, we find that the system clock of an embedded system and desktop computers all accord with the demand of the PTPd, and the PTPd can be used as a software time measurement tool in the submicrosecond range.