Showing papers on "Precision Time Protocol published in 2009"

The white rabbit project

Abstract: Reliable, fast and deterministic transmission of control information in a network is a need for many distributed systems. One example is timing systems, where a reference frequency is used to accurately schedule time-critical messages. The White Rabbit (WR) project is a multi-laboratory and multi-company effort to bring together the best of the data transfer and timing worlds in a completely open design. It takes advantage of the latest developments for improving timing over Ethernet, such as IEEE 1588 (Precision Time Protocol) and Synchronous Ethernet. The presented approach aims for a general purpose, fieldbus-like transmission system, which provides deterministic data and timing (sub-ns accuracy and ps jitter) to around 1000 stations. It automatically compensates for fiber lengths in the order of 10 km. This paper describes the WR design goals and the specification used for the project. It goes on to describe the central component of the WR system structure the WR switch - with theoretical considerations about the requirements. Finally, it presents real timing measurements for the first prototypes of WR hardware.

Synchronization Performance of the Precision Time Protocol in Industrial Automation Networks

Abstract: This paper analyzes the factors that affect the synchronization performance in peer-to-peer precision time protocol (PTP). We first study the influence of frequency drift in the absence of jitter and compare the gravity of the master drift with that of the slave drift. Then, we study the influence of jitter under the assumption of constant frequencies and the effect of averaging. The analytic formulas provide a theoretical ground for understanding the simulation results, some of which are presented, as well as the guidelines for choosing both system and control parameters.

Optimal Synchronization of Local Clocks by GPS 1PPS Signals Using Predictive FIR Filters

Abstract: In this paper, we discuss optimal synchronization of local clocks using Global Positioning System (GPS) one-pulse-per-second (1PPS) timing signals. To eliminate sawtooth errors that are peculiar to the 1PPS signals and optimally steer the clock errors each M seconds, we propose the use of a ramp-predictive finite-impulse-response (FIR) filter that is known to be optimal for clock models on large averaging horizons. A low-pass filter is used to smooth the hold filter output between the optimally predicted points. A GPS-locked crystal clock has been investigated in detail in terms of the time interval error, Allan deviation, and precision time protocol (PTP) variance. A high-efficiency implementation of the proposed synchronization algorithm is experimentally demonstrated.

Precision Time Synchronization Using IEEE 1588 for Wireless Sensor Networks

Abstract: Wireless sensor networks are evolving from relatively undemanding applications to applications which have stronger requirements. The coordination of distributed entities and events requires time synchronization. Although a number of methods have been studied for WSNs, some applications require high precision time synchronization. Precision time synchronization enables a variety of extensions of applications. The IEEE 1588 precision time protocol (PTP) provides a standard method to synchronize devices in a network with sub-microsecond precision. This paper deals with precision time synchronization using IEEE 1588 over wireless sensor networks. Precision time synchronization using IEEE 1588 provides compatibility between heterogeneous systems in WSNs. This paper also presents experiments and performance evaluation of precision time synchronization in WSNs. Our result established a method for nodes in a network to maintain their clocks to within a 200 nanosecond offset from the reference clock of a master node.

Performance analysis of Kalman filter-based clock synchronization in IEEE 1588 networks

Abstract: This paper analyzes the effects on synchronization performances of the accuracy of skew and offset estimates, the short and long-term stability of the unregulated clock, the rate at which timing information is exchanged within the network The work makes use of a simulated clock based on the state-variable model, for which realistic parameters are obtained from experimental measurements of Allan variance plots for different kinds of clocks

Ten Microseconds Over LAN, for Free (Extended)

Abstract: The status quo for time stamping in personal computers (PCs) is ntpd, which, under general conditions, is accurate to 1 ms at best. For precision applications, it is inadequate, but it is a low-cost solution that suits many generic applications. IEEE-1588 provides mechanisms for submicrosecond accuracy, but to achieve this, more hardware is needed. We have developed the TSCclock, which gives the performance between these two solutions [about 10 mus on a local area network (LAN)] beyond submilliseconds using commodity hardware. We benchmark the TSCclock to show its potential as an inexpensive yet accurate software clock, which can be used with IEEE-1588 for LANs but has wider applicability as a replacement to ntpd.

Packet delay variation management for a better IEEE1588V2 performance

Abstract: Designed for the distribution of time, IEEE 1588V2 also called as Precision Time Protocol V2 (PTPV2) is often referred to as a key candidate for synchronization over Packet Switched Networks (PSNs). Unfortunately, as the IETF's Network Time Protocol and unlike the ITU-T's Synchronous Ethernet, the performance of this protocol strongly depends on Packet Delay Variations (PDVs) produced by the telecom network environment. Such behavior represents a strong issue, particularly considering the severe synchronization requirements of the mobile backhaul segment. This article focuses on different manners to control and to fight out PDVs. After discussing PDV-management principles, via the illustration of some existing mechanisms, we propose a new distributed ranging scheme which allows for optimizing the overall PTPV2 synchronization performance. Finally, considered as a critical mobile backhaul use case, IEEE 1588V2 over Digital Subscriber Line (DSL) is investigated regarding PDV concerns.

Application of IEEE 1588 to the measurement of synchrophasors in electric power systems

Abstract: This paper investigates the possibility of using the PTP (Precision Time Protocol) defined in the Standard IEEE 1588 for applications in electric power system, with reference to one of the most challenging measurement problems, i.e. the measurement of synchrophasors. The proposed approach refers to situations in which many measurement devices, connected to each other by suitable communication links, are located in a geographically limited sub-area of the power system. A laboratory experimental setup has been built to evaluate the performance achievable with this solution in terms of both accuracy and robustness. A detailed analysis of the obtained results is presented.

Strategies to secure the IEEE 1588 protocol in digital substation automation

Abstract: The IEEE 1588 Precision Time Protocol seems to be a promising way to handle the synchronization requirements of tomorrow's substation automation based on IEC 61850. While a specific working group is tackling the security aspects of the protocols defined by IEC 61850, a secure IEEE 1588 protocol remains mostly uncovered in the specific context of substation automation. In this paper, we are focusing on securing IEEE 1588 for substation automation. We are analyzing and classifying the different attacks relevant for a substation and proposing a way to handle the logical disconnection of the time server and its clients that appears whenever an attack occurs. The method based on clock drift correction allows to keep a node synchronized for different period of time depending on the correction mechanism used. The implementation and experiments of the different drift correction mechanisms shows the tradeoff between the accuracy of the correction and the required computational time. By analyzing the different experiments, we can then match the computational power of a class of devices present in a substation and a correction technique.

Wireless network synchronization for multichannel multimedia services

Abstract: When a single source of multimedia contents is distributed to multiple reproduction devices, the audio and video contents require synchronous play for multi-channel stereo sound and lip-synchronization. This paper investigates capability of IEEE 802.11n wireless LANs for providing synchronized services of real-time multimedia traffic. We implement IEEE 1588 Precision Time Protocol in wireless LAN devices to characterize delay jitter and clock synchronization accuracy. The results indicate a strong potential to provide a high fidelity real-time multi-channel multimedia networking service within 430-microsecond synchronization accuracy at an approximately 80 Mbps streaming rate.

A master-slave synchronization model for enhanced servo clock design

Abstract: Slave servo clocks have an essential role in hardware and software synchronization techniques based on Precision Time Protocol (PTP). The objective of servo clocks is to remove the drift between slave and master nodes, while keeping the output timing jitter within given uncertainty boundaries. Up to now, no univocal criteria exist for servo clock design. In fact, the relationship between controller design, performances and uncertainty sources is quite evanescent. In this paper, we propose a quite simple, but exhaustive linear model, which is expected to be used in the design of enhanced servo clock architectures.

Precision timing in the NEPTUNE Canada network

Abstract: Delivery of accurate timing to subsea instruments is one of the essential functions of the NEPTUNE Canada ocean observatory. In the context of an ocean observing system, “timing” is understood to mean the ability to timestamp data using a clock which is traceable to Universal Time Coordinates (UTC) within some desired level of precision. Transmission or delivery of timing means transporting the necessary timing signals and data to subsea instruments or data collection processors. Timing signals are conventionally delivered in the form of a logic state transition on a dedicated communications line followed by a data string indicating the time at which the transition occurred. NEPTUNE Canada employs Ethernet communications channels to deliver timing. This avoids the need to provision additional communications channels and ensure that timing signals are available at all points within the network. The disadvantage of this approach is that timing signals must share the communications channels on which data is transmitted and may suffer delays or packet loss. Three timing protocols are employed: Network Time Protocol (NTP) described in IETF RFC 1305, Simple Network Time Protocol (SNTP) as described in RFC 2030 and IEEE 1588 Precision Time Protocol (PTP) per IEEE 1588. NTP/SNTP are generally accepted to be accurate to within a few milliseconds and are suitable for a wide variety of applications. PTP provides significantly better accuracy which is required for applications such as seismology and acoustic thermography. Master clocks located in the shore station acquire time from the Global Positioning System for transmission to subsea instruments. Alcatel-Lucent Submarine Networks and NEPTUNE Canada have successfully demonstrated PTP operation on a test bed which is representative of the NEPTUNE Canada network under simulated data traffic conditions, achieving a precision of ±10 microseconds or better. Ongoing development of IEEE 1588 will allow precision to within 100s of nanoseconds in future observatories. Science instruments which can take advantage of PTP timing delivery are currently under development.

The Research of Precision Time Protocol IEEE 1588

Abstract: The IEEE standard precision time protocol(PTP) IEEE 1588 is at present a very comprehensive solution for highly precise time synchronization in an Ethernet network for its many advantages over the traditional power station time synchronization protocol,such as the network time protocol(NTP).The core algorithms of the IEEE 1588,the best master clock(BMC) algorithm and the local clock synchronization(LCS) algorithm,are analyzed.A solution is proposed for the situation in which the protocol is incapable of meeting its assumptions in actual application.The protocol is finally realized and tested based on an ARM9200 platform in laboratory surroundings,with evidently better accuracy than NTP.The research is of great significance for actual power system application.

Olm: A Hands-on Approach

Abstract: With increasing costs and shrinking budgets, there is considerable economic pressure to get the most out of existing aircraft extending their in-service life if possible and to do so in a manner that does not compromise flight safety. One of the methods to achieve this is Operational Loads Monitoring (OLM). This paper presents an overview of military aircraft OLM programs, the typical parameters they measure and how they store and analyse the data. The research utilizes case studies of four aircraft for which ACRA CONTROL provided the data acquisition systems. The paper focuses on the data acquisition technology used to measure the flight parameters, the data processing and storage and how this data is processed on the ground. Finally, some of the technology and other improvements that have allowed newer OLM systems to provide a better fatigue profile of the aircraft are described.

A delay control method in the passive optical network, an optical line terminal and a passive optical network

Abstract: A delay control method in the passive optical network, an optical line terminal and a passive optical network are provided. The delay control method in the passive optical network transmits the precision time protocol message in the direction of downlink, and the method includes: obtaining the buffer time of the precision time protocol message sent to the optical network unit (21); storing the precision time protocol message sent to the optical network unit, when the storing time being equal to the buffer time, sending the precision time protocol message to the optical network unit (22).

Distributed Ethernet Network of Advanced Pedestrian Signals

Abstract: For more than 60 years, traffic signals have used direct wire connections between the traffic controller cabinet and the signals and detectors dispersed throughout the intersection. A network-based approach is reported for distributed control and sensing of traffic signal devices. The motivation of this research has been to improve safety and performance while reducing the cost of a signalized intersection installation. An Ethernet-based network architecture is presented that uses the National Transportation Communications for Intelligent Transportation Systems Protocol (NTCIP) for real-time signal control combined with the IEEE 1588 precision time protocol for robust operation of safety-critical applications synthesized into the term "smart signals." The investigation focuses on improving accessibility and safety for pedestrians through the use of smart signals. The smart signal paradigm is the basis of an enabling technology that permits complex functioning signals and detectors with self-test capabilit...

Clock synchronization based on distributed hidden state estimation

Abstract: This paper presents a novel clock synchronization algorithm based on the Transparent Clock mechanism of peer-to-peer Precision Time Protocol. To model the dynamics of the oscillator and the influence of the uncertainties, e.g., random stamping and quantization errors, on the synchronization performance, clock synchronization is formulated as a probabilistic inference problem which can be solved by a distributed hidden state estimation method such as the sum-product algorithm. The performance of this approach is verified by numerical results.

Efficient predictive steering of local clocks in GPS-based timekeeping

Abstract: We discuss optimal synchronization of local clocks by the Global Positioning System (GPS) one pulse per second (1PPS) timing signals. To eliminate sawtooth errors peculiar to the 1PPS signals and optimally steer the clock errors each M seconds, we propose using a ramp predictive finite impulse response (FIR) filter that is known to be optimal for clock models on large averaging horizons. A low-pass filter is used to smooth the hold filter output between the optimally predicted points. A GPS locked crystal clock has been investigated in detail in terms of the time interval error, Allan deviation, and precision time protocol (PTP) variance. A high efficiency implementation of the proposed synchronization algorithm is demonstrated experimentally.

Swarm synchronization for multi-recipient multimedia streaming

Abstract: IP networks allow constructing versatile device configurations for multimedia streaming. However, the stochastic nature of the packet-switched data transmission may complicate IP-based implementations of some conventional applications such as analog wired transmission of synchronized multi-channel audio. This paper introduces a multimedia streaming system based on the synchronization of multiple playback clients as a ‘swarm’. The proposed ‘swarm synchronization’ mechanism is based on precise clock synchronization with the PTP protocol and adjusting the client-specific sampling rates according to the true playback rates of other clients. A streamlined version of the RTP protocol is employed to minimize playout delay. The proposed system is empirically evaluated in wired Ethernet LAN and in wireless IEEE 802.11g LAN. The experimental results show that in the Ethernet network the proposed streaming system is able to achieve very precise synchronization.

A probabilistic approach to clock synchronization of cascaded network elements

Abstract: Precision Time Protocol (PTP) synchronizes clocks of networked elements by exchanging messages containing precise time-stamps. Based on the available timing information, different algorithms can be developed for the clock synchronization. This paper introduces a novel PTP-based method in which clock synchronization is formulated as a probabilistic inference problem and is solved by Kalman filtering. The performance of this approach is verified by numerical results.

Research and application of IEEE1588 precision time protocol

Abstract: To develop the technology of time synchronize between NodeB and radio network controller(RNC) in TD-SCDMA,and change the status of global position system(GPS) as the only way to synchronize time,IEEE1588 V1 and IEEE1588 V2 are studied.Network time protocol(NTP) and simple network time protocol(SNTP) are also studied and compared with IEEE1588.IEEE1588 has higher time precision and accord with the TD-SCDMA system time precision requirement is proved.A solution base on the existing telecom network using IEEE1588 is proposed.

PTP interworking 802.15.4 using 6LoWPAN

Abstract: Network Time Protocol (NTP) and Precision Time Protocol (PTP) have been used for time synchronization in many year. These protocols are not appropriated for IP over 802.15.4 like heterogeneous network because these are using Ethernet. To cope with this difficulty, we proposed IP over 802.15.4 time synchronization using 6LoWPAN (IPv6 over Low power Wireless Personal Area Networks) we could get accurate and precision time synchronization due to sending single packet. We implement IP over 802.15.4 FPGA board.

Study on time-synchronization networking of power system

Abstract: The article introduces the present situation of time-synchronization networking in substations of power system, analyses the risk of GPS dependence, compares the time precision of different application systems in substations and the results of using NTP/DCLS/PTP networking. It suggests that the flat structure could be used as the main choice in timesynchronization networking and DCLS mode is used as the standby for emergency situation.

Ethernet backhaul architecture

Abstract: A communication system for providing an accurate timing signal and synchronization information is described herein. The communication system comprises a Precision Time Protocol (PTP) server, a Global Positioning System (GPS), a pseudowire device, and a PTP client. The PTP client receives a time of day data and frequency information from the PTP server, receives a timing signal from the GPS, synchronizes the time of day data and timing signal to create synchronized a time of day signal, and provides the synchronized time of day signal to the pseudowire device. The pseudowire device processes the synchronized time of day signal and the frequency information to perform a time-division multiplexing signal to Ethernet signal synchronized conversion.

Collision avoidance for Delay_req messages in broadcast media

Abstract: The time accuracy of the Precision Time Protocol deteriorates in consequence to Delayreq/Delayresp session collisions common for applications using shared broadcast media. In this paper we propose a protocol that coordinates Delay_req/Delay_resp sessions with minimum changes to the original PTP protocol. Simulations illustrate protocol's operation and demonstrate significant reduction of session collisions.

Clock Synchronization and Its Implementation in CE/PTN

Abstract: IEEE1588 can be used to implement clock synchronizing in Carrier Ethernet network.This paper firstly introduce the protocol of IEEE1588,then derive the formula to how to calculate the clock synchronizing,and at last use FPGA to implement it.

Progress in portable instrumentation for time source verification and analysis

Abstract: The calibration of the internal GPS-slaved reference clock of a portable time measuring instrument has been carried out using GPS Common View and we report on the subsequent direct measurement of the reference accuracy and stability over different time periods. The measurement architecture has been extended to include Grand Master time sources that conform to IEEE Std 1588 PTP (Precision Time Protocol). Time-code interpretation, network packet capture and time-stamping are performed by a programmable logic array (FPGA) and network transceiver (PHY) combination. This approach eliminates sources of imprecision which are found in traditional software based network package capture systems. Once captured, packets are interpreted by a specialized PTP protocol stack capable of automatically classifying PTPv1 and PTPv2 without the involvement of the operator.

Analyze and Improve the Time Synchronization in EPA

Abstract: In order to improve the time synchronization precision to insure the communication timely, several types of clock synchronization methods were compared, analyzed the IEEE1588 clock synchronization system, discussed the PTP system software programming, introduced some source code transplanting methods, got the root cause of the low precision, provided three major improving methods, tested the improved system, the results indicate the high precision time synchronization has been attained.

Design and Implementation of PTP Gateway to Extend IEEE 1588 to Zigbee networks

Abstract: The coordination of distributed entities and events requires time synchronization. Precision time synchronization enables a variety of extensions of applications and provides much accurate information. The IEEE 1588 precision time protocol (PTP) provides a standard method to synchronize devices in a network. This paper deals with the design and implementation of a PTP gateway to extend IEEE 1588 to Zigbee networks. The PTP gateway can not only extend IEEE 1588 to Zigbee networks but also share the same time reference using IEEE 1588 between two or more Zigbee networks. This paper also presents experiments and performance evaluation of time synchronization using the PTP gateway. Our result established a method for nodes in a network to maintain their clocks to within a 300 nanosecond offset from the reference clock of a master node via Ethernet.