Showing papers on "Precision Time Protocol published in 2015"

Understanding and applying precision time protocol

Abstract: Precise time synchronization has become a critical component of modern power systems. There are several available methods for synchronizing the intelligent electronic devices (IEDs) in a power system. In recent years, there has been great interest in providing time to the IEDs using the same infrastructure through which the data are communicated. Precision Time Protocol (PTP) is a promising technology for achieving submicrosecond synchronization accuracy between IEDs over Ethernet. This paper presents the protocol fundamentals and discusses considerations for designing power system networks to achieve submicrosecond accuracies. Specific provisions made in the profile for power system applications to support IEC 61850 substation automation systems are also discussed.

A method for robust ptp synchronization with default 1588v2 profile

Abstract: Exemplary methods for reducing sync time in a precision time protocol (PTP) network include receiving, by a first PTP slave port of a first network device, timing messages from a second PTP master port of a second network device. The methods include maintaining a PTP master clock based on timing information included in the timing messages received from the second network device via the first PTP port. The methods further include receiving, by a third PTP passive port of the first network device, timing messages from a fourth PTP master port of a third network device. The methods include determining the third PTP passive port is a protective passive port based on a stepsRemoved value of the third network device, and maintaining an auxiliary clock based on the timing information included in the timing messages received from the third network device via the third PTP port.

Skewless network clock synchronization without discontinuity: convergence and performance

Abstract: 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.

Improving the PTP synchronization accuracy under asymmetric delay conditions

Abstract: Tight synchronization timing is expected to play a crucial role for the realization of emerging Internet of Things (IoT) high value real-time applications such as smart transportation and smart grid. Most packet-based synchronization protocols require two-way communications delay symmetry for precise accuracy. The Precision Time Protocol (PTP) provides mechanisms to measure and take into account the delay asymmetry problem, such as the residence time measurements, but recommend PTP support at all nodes. In this paper, we consider partial on-path PTP support, where a subset of the nodes are PTP unaware. We propose probing-based mechanisms in order to estimate asymmetry and improve the synchronization performance. The extensive simulation results show that the proposed lightweight per-packet asymmetry mitigation (PPAM) mechanism, aiming at estimating the per-packet delay components, outperforms the other considered protocols mainly at low to mid network loads, while under certain conditions the regular PTP with QoS support provides more stable synchronization accuracy.

Time-Complemented Event-Driven Architecture for Distributed Automation Systems

Abstract: Time-driven and event-driven control models are two fundamental design paradigms applied in distributed control systems for synchronizing decentralized activities This paper proposes a unified architecture for combining both approaches The combination offers the best of both worlds’ properties, such as the expressiveness of event-driven programming and the determinism of time-driven logic The foundations of this symbiosis are the IEC 61499 Function Block standard providing event-driven distributed control architecture and the IEEE 1588 Precision Time Protocol establishing the basis for highly-accurate time synchronization The proposed time-complemented event-driven distributed control model aims at improving the modularity and flexibility of automation software with satisfactory control performance The new control model has been compared with conventional centralized and distributed control approaches analytically and by simulation The comparison results reveal that the proposed control model is efficient and flexible Finally, a reference example has been used to demonstrate merits of the new approach

Apparatus and Method to Use PTP Timestamps for One-Way Delay and Delay Variation Measurement in IP Networks

Abstract: A method is implemented by a network device to establish a one-way active measurement protocol (OWAMP) test session that supports use of a Network Time Protocol (NTP) timestamp format and a Precision Time Protocol Version 2 (PTPv2) timestamp format. The network device acts as a control-client that communicates with a server to establish an OWAMP test session between a sender and a receiver. The method includes receiving a server greeting message from the server indicating timestamp formats that the receiver can interpret, checking whether the receiver supports the multiple timestamp format extensions to OWAMP, configuring the sender to set timestamps in a format that the sender can set and the receiver can interpret if the receiver supports multiple timestamp format extensions to OWAMP, sending an extended set-up-response message to the server indicating a timestamp format that the sender can set and the receiver can interpret, and receiving a server-start message from the server.

An implementation of IEEE 1588 protocol for IEEE 802.11 WLAN

Abstract: Clock synchronization is one of the enabling technologies for Wireless Local Area Networks (WLAN). It is crucial to perform applications such as data fusion, location detection and energy conservation. IEEE 1588 Precision Time Protocol (PTP) is a widely used clock synchronization protocol, but its accuracy is affected by bidirectional asymmetric delays in WLAN. A detailed analysis of the generation mechanism and statistical properties of the bidirectional asymmetric delays in IEEE 802.11 WLAN is conducted firstly. Then, a Kalman filter is designed for delay filtering. And based on the Kalman filter, a clock servo system is proposed using pure software-based implementation of PTP for IEEE 802.11 WLAN. Finally, the effectiveness of the implementation is verified by experiments. Experimental results show that the implementation has the virtues of high synchronization accuracy, short convergence time and small deviation error.

Enhanced synchronization accuracy in IEEE1588

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

A detection and mitigation model for PTP delay attack in a smart grid substation

Abstract: Smart grid applications demand the availability of a reliable and accurate time signal. Measurements and events need to be correctly aligned to enable proper actions and decisions. Precision Time Protocol (PTP) is the favored protocol for time distribution across smart grid domains. The correct functionality of PTP is of paramount importance and its security is of high priority. To harden its security, detection and prevention mechanisms against attacks targeting PTP are needed. In this paper, we propose detection and mitigation mechanisms against the known PTP delay attack. We apply model checking to quantify the effect of the delay attack. Moreover, the validity of the proposed mechanism is formally proven. The collected results support the usefulness of the mechanism in detecting the delay attacks targeting PTP, and preserving the system functionality.

Synchronizing Clocks in a Communications Network

Abstract: A User Equipment comprises a master clock, for example a Precision Time Protocol, PTP, or Precision Time Control Protocol, PTCP, network clock. The User Equipment further comprises circuitry configured to set the master clock based on signals from a wireless communications network node and a time offset, wherein the time offset is based on the propagation delay between the wireless network node and the User Equipment. The circuitry is further configured to send timing information to a network device in a communications network having a slave clock, whereby the network device can synchronize its slave clock with respect to the master clock comprised within the User Equipment.

Investigation of white rabbit for synchronization and timing of netted radar

Abstract: White Rabbit (WR) emerged as an OpenSource and OpenHardware project from CERN, due to stringent timing requirements for data recording in the Large Hadron Collider project. It provides picosecond accuracy timing based on a 1 Gigabit Ethernet (1GE) fibre data network, where all routers are specialised White Rabbit hardware. WR is built over the IEEE Precision Time Protocol (PTP IEEE 1588-2008). The operation of networks of radar sensors requires precision time distribution for collaborative target location, as well as excellent, low phase noise to enable precision Doppler measurements. This paper investigates the potential of the WR for network radar, and compares it to other possible solutions. The radar requirements are defined, followed by WR architectures that could meet these needs. The need of WR for a fibre link is clearly an issue for some applications. A series of experiments in progress are described.

System and method for clock synchronization in a wireless backhaul network using IEEE 1588 precision time protocol

Abstract: A method and system is disclosed for clock synchronization in a wireless backhaul network, based on the IEEE1588 Precision Time Protocol (PTP) The network comprises a plurality of hubs, each hub serving one or more remote backhaul modules Each hub comprises a slave clock, which communicates with a master clock through forward and reverse links The method comprises, for each hub, estimating the frequency drift {circumflex over (α)} and offset {circumflex over (β)} from the forward and reverse links between the master and slave clock, estimating the accuracy of {circumflex over (α)} and {circumflex over (β)}, determining the least congested link, and adjusting the frequency of the slave clock based on {circumflex over (α)} and {circumflex over (β)} from the least congested link A fixed or variable time window size is selected to achieve a desired accuracy of {circumflex over (α)} and {circumflex over (β)} The method may comprise estimating a maximum holdover time for maintaining synchronization with a desired confidence level

Ns-level time transfer over a microwave link using the PTP-WR protocol

Abstract: Today it is possible to achieve sub-ns level time synchronization on a wireline network while only us-level synchronization can be achieved on a wireless (microwave) link. In this paper we will, first, study the performances of different time synchronization wireline based protocols, such as Precision Time Protocol (PTP), Synchronous Ethernet (SyncE) and PTP White Rabbit (PTP-WR). And then, we will present our results using a wireless link, and determine which radio technology can achieve ns range time synchronization. Our motivation is to qualify a time transfer process operating over microwave link and offering secured GNSS-like time performance.

ptp++: A Precision Time Protocol Simulation Model for OMNeT++ / INET

Abstract: Precise time synchronization is expected to play a key role in emerging distributed and real-time applications such as the smart grid and Internet of Things (IoT) based applications. The Precision Time Protocol (PTP) is currently viewed as one of the main synchronization solutions over a packet-switched network, which supports microsecond synchronization accuracy. In this paper, we present a PTP simulation model for OMNeT++ INET, which allows to investigate the synchronization accuracy under different network configurations and conditions. To show some illustrative simulation results using the developed module, we investigate on the network load fluctuations and their impacts on the PTP performance by considering a network with class- based quality-of-service (QoS) support. The simulation results show that the network load significantly affects the network delay symmetry, and investigate a new technique called class probing to improve the PTP accuracy and mitigate the load fluctuation effects. I. INTRODUCTION

Online Incremental Clock Synchronization

Abstract: Time synchronization is a fundamental requirement for many services provided by distributed systems. For this purpose, several time synchronization protocols have been proposed. However, they either achieve high accuracy by adding further network traffic, even more than common protocols such as network time protocol and precision time protocol, or consume a lot of time in additional computations. An online distributed tracing and monitoring system, used to identify functional and performance problems in distributed systems, must offer high precision with minimum time overhead and system resource consumption. The aim of this paper is to propose an efficient algorithm for time synchronization in online mode, applicable for all distributed services. The proposed method in this paper addresses five key requirements for a practical solution in distributed systems. First, it provides microseconds scale accuracy, which is applicable for trace events with nanosecond timestamp granularity. Secondly, it does not require adding new network traffic, using the send and receive time of existing traffic. Thirdly, it synchronizes the distributed traces in average time complexity of O(1) per synchronization update. Fourthly, it updates online synchronization parameters immediately without latency. Finally, it iteratively refines the early estimates without requiring significant buffering of earlier data. Although we used this work for distributed trace synchronization, it is a general, fully incremental, continuous synchronization approach applicable to most synchronization purposes.

Approximate Synchrony: An Abstraction for Distributed Almost-Synchronous Systems

Abstract: Forms of synchrony can greatly simplify modeling, design, and verification of distributed systems. Thus, recent advances in clock synchronization protocols and their adoption hold promise for system design. However, these protocols synchronize the distributed clocks only within a certain tolerance, and there are transient phases while synchronization is still being achieved. Abstractions used for modeling and verification of such systems should accurately capture these imperfections that cause the system to only be “almost synchronized.” In this paper, we present approximate synchrony, a sound and tunable abstraction for verification of almost-synchronous systems. We show how approximate synchrony can be used for verification of both time synchronization protocols and applications running on top of them. We provide an algorithmic approach for constructing this abstraction for symmetric, almost-synchronous systems, a subclass of almost-synchronous systems. Moreover, we show how approximate synchrony also provides a useful strategy to guide state-space exploration. We have implemented approximate synchrony as a part of a model checker and used it to verify models of the Best Master Clock (BMC) algorithm, the core component of the IEEE 1588 precision time protocol, as well as the time-synchronized channel hopping protocol that is part of the IEEE 802.15.4e standard.

Synchronization precision monitoring system of time synchronization device of power equipment

Abstract: The invention discloses a synchronization precision monitoring system of a time synchronization device of power equipment. The synchronization precision monitoring system comprises a center monitoring system, a network management system and a measurement device. The measurement device is arranged in a transformer substation and is connected with master clock equipment, expanded clock equipment and equipment with time service which are in the transformer substation. The measurement device acquires a time signal of the master clock equipment in the transformer substation, converts the time signal into a precision time protocol (PTP) message packaged by E1, and then transmits to the center monitoring system through an E1 channel of an interstation synchronous digital hierarchy (SDH); the center monitoring system restores according to the PTP message so as to acquire the time signal of a master clock of the transformer substation, compares the time of the master clock of the transformer substation with current time so as to acquire a first time difference, and transmits the first time difference to the network management system; and the measurement device confirms a second time difference between the time of the master clock equipment and the time of the expanded clock equipment and the equipment with time service in the transformer substation, and transmits the second time difference to the network management system. The synchronization precision monitoring system can acquire the output accuracy of the time synchronization device in time.

A synchronous Gigabit Ethernet protocol stack for high-throughput UDP/IP applications

Abstract: State of the art detector readout electronics require high-throughput data acquisition (DAQ) systems. In many applications, e. g. for medical imaging, the front-end electronics are set up as separate modules in a distributed DAQ. A standardized interface between the modules and a central data unit is essential. The requirements on such an interface are varied, but demand almost always a high throughput of data. Beyond this challenge, a Gigabit Ethernet interface is predestined for the broad requirements of Systems-on-a-Chip (SoC) up to large-scale DAQ systems. We have implemented an embedded protocol stack for a Field Programmable Gate Array (FPGA) capable of high-throughput data transmission and clock synchronization. A versatile stack architecture for the User Datagram Protocol (UDP) and Internet Control Message Protocol (ICMP) over Internet Protocol (IP) such as Address Resolution Protocol (ARP) as well as Precision Time Protocol (PTP) is presented. With a point-to-point connection to a host in a MicroTCA system we achieved the theoretical maximum data throughput limited by UDP both for 1000BASE-T and 1000BASE-KX links. Furthermore, we show that the random jitter of a synchronous clock over a 1000BASE-T link for a PTP application is below 60 ps.

Synchronization of phasor measurement units and its error propagation to state estimators

Abstract: The recent breakthrough on power grid technologies was promoted by the emergence of phasor measurement units (PMUs), as they provide direct and high-rate data for analyzing and controlling the network. Time becomes critical however, since offsets in the internal clocks of PMUs render their data unreliable. In this context, the present work describes grid-wide implementation of a Precision Time Protocol system to deliver an accurate time reference to PMUs at different power stations. Residual time offsets are modeled as PMU noise, propagating to linear state estimators, and their non-linear counterparts that result from combining PMU and power flow data.

Video event recording system

Abstract: An Ethernet/IP process or network based video event recording system is provided, which is to be embedded into any production line (conveyor belt), providing a continuous high speed loop recording with a specially designed video recording and viewing software, synchronized with the factory precision time protocol server (IEEE 1588 server), and able to store and retrieve files on or from a remote server. A web based management interface is provided for remote control, as well as to retrieve and view the recorded images and videos. The video recording system is designed to be connected to the factory network and to work seamlessly with the standard factory timing protocols and standards, as well as the standard factory programmable logic controllers.

Timestamp Reliability of the Schenberg Gravitational Wave Detector Data Acquisition System

Abstract: 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.

Performance analysis of time synchronization precision of PTP in smart substations

Abstract: The precision time protocol (PTP) is fundamentally recommended in smart substations, which could potentially result in further weakening the power system. However, defects of domestic PTP devices restrict the spread of the application of PTP in smart substations. In this paper, the computation of the PTP offset in different clock modes from the two editions of 1588 standards is analyzed theoretically. Test platforms are built to study the timing accuracy of PTP performance under certain circumstances. Especially, a time synchronizing precision test is conducted under the network dataflow including certain messages like PTP, Generic Object Oriented Substation Event (GOOSE) and Sampled Value (SV). In terms of synchronizing precision and stability, the “PTP straight link” test shows that P2P is better than E2E, and that ETH is better than UDP. And the effect of boundary and transparent clock shows that the one-step “P2P-ETH” transparent clock will fulfill the application requirement in smart substation. The last test indicates that the network traffic which consists of such messages enlarge the jitter of PTP synchronization. And comprehensively, the one-step “P2P-ETH” transparent clock is suitable in smart substation.

Apparatus and method to efficiently use the ptp timestamp for one-way delay and delay variation measurement in ip networks

Abstract: A method is implemented by a network device to establish a one-way active measurement protocol (OWAMP) test session to verify that a session-sender and session-reflector support a timestamp format extension including a Precision Time Protocol Version 2 (PTPv2) timestamp format. The PTPv2 timestamp format is to be utilized in place of a Network Time Protocol (NTP) timestamp format. The network device acts as a control-client that communicates with a server to establish an OWAMP test session between the session-sender and the session-receiver.

Method for precision time protocol synchronization network and apparatus

Abstract: Embodiments relate to the field of communications, and provide a method for a PTP synchronization network and an apparatus, which help to reduce costs of obtaining performance of a Precision Time Protocol synchronization network The method includes: executing, by a slave clock apparatus, an operation of time synchronization with a first apparatus according to the PTP through a first port; setting a state of a second port of the slave clock apparatus to slave; obtaining information required for determining a time offset between the slave clock apparatus and a second apparatus; determining an offset according to the information; if an absolute value of the offset is greater than a threshold, determining that time synchronization performance of a first link is faulty or time synchronization performance of a second link is faulty; and sending a message to a third apparatus

Transporting Timing messages over MPLS Networks

Abstract: This document defines a method for transporting timing messages, such as Precision Time Protocol (PTP) or Network Time Protocol (NTP), over a Multiprotocol Label Switched (MPLS) network. The method facilitates efficient recognition of timing packets to enable their port level processing in both Label Edge Routers (LERs) and Label Switched Routers (LSRs). The basic mechanism is to transport timing messages inside "Timing LSPs", which are dedicated MPLS Label Switched Paths (LSPs) that carry only timing, and possibly related Operations, Administration and Maintenance (OAM) or management packets, but do not carry customer traffic. Two encapsulations methods are defined. The first transports UDP/IP encapsulated timing messages directly over the dedicated LSP. The second transports Ethernet encapsuled timing messages inside an Ethernet pseudowire.

Method, system and device for providing time-stamps in a network measurement test

Abstract: A method, system and device are presented to improve the accuracy for time-stamps provide to a network measurement tools like Bandwidth Available Real-time (BART), or Two-Way Active Measurement Protocol (TWAMP). Time-stamps for these tools are based on a Precision Time Protocol (PTP) received by a PTP slave node, initializing the network measurement test. By introducing a local clock in a first embodiment, system calls, involving delays in scheduling and interrupts are prevented, thereby obtaining more accurate PTP and TWAMP measurements. In a second embodiment a timing information of a PTP message received is applied in an already prepared message in a network measurement test, such that processing of the message is minimised, resulting in an accurate timing information in e.g. a TWAMP network measurement test.

On the accuracy of packet-based measurements in the PTP telecom profile

Abstract: Recent years have witnessed an increased interest in Precision Time Protocol (PTP) in telecommunication networks, either as an alternative to Global Positioning System (GPS) or as synchronization back-up. To achieve node synchronization at the μs-level, very accurate measurements of time offsets are needed. However, unless PTP is fully supported throughout the network, timing packets may be subjected to propagation delays whose variability can significantly impair measurement. In the PTP telecommunication profile Sync packets can be broadcast at high rate, providing a slave node with statistical information that can be employed to detect and estimate such network effects. The accuracy of these estimates is analyzed in the paper, which considers the assumed underlying probability models and discusses statistical aspects for PTP packets affected by variable queuing delays. Characteristics of packet selection algorithms in ITU-T Recommendations are analyzed, providing indications on performance.

Transparent clock characterization using IEEE 1588 PTP timestamping probe

Abstract: As new application areas like SmartGrids and 4G cellular mobile backhaul networks emerge, requirements on precision of the frequency and time synchronization increase. IEEE 1588v2 Precision Time Protocol (PTP) offers sub-microsecond synchronization precision using conventional Ethernet networks. In practical network scenarios the PTP performance is greatly reduced due to varying queuing latencies introduced by the network's switching and routing devices. This drawback has been overcome with the introduction of network devices with a Transparent Clock (TC) functionality defined in the IEEE 1588v2 PTP standard. As different vendors use proprietary implementations of the TC mechanism, it becomes essential to characterize TC's accuracy. Literature survey revealed that so far two measurement techniques have been proposed for that purpose, however, a comprehensive study of the measurement's error with regards to hardware imprecisions have not yet been published. In this paper we provide a thorough mathematical analysis with respect to hardware limitations of the TC measurement techniques and based on this analysis measurement calibrations are introduced. Moreover, we propose a new measurement setup that requires less expensive hardware yet maintains similar precision to prior art techniques. The new setup is provided with a detailed proof of concept and an experimental verification through measurements.