Enhancements to the time synchronization standard IEEE-1588 for a system of cascaded bridges
22 Sep 2004-pp 239-244
TL;DR: In this paper, a bypass clock instead of the boundary clock is proposed as an enhancement of the IEEE-1588 standard for bridged networks, where the local clock adjustment can be modeled by a corresponding control loop.
Abstract: The IEEE-1588 standard for a high precision time synchronization now exists since 2002. For using this standard in bridged networks a so-called boundary clock is defined, where the local clock adjustment can be modeled by a corresponding control loop. At the field level of industrial automation systems, the line topology is very important. By using Ethernet at the field level, the resulting chain of bridges leads to a cascade of control loops and may lead to instabilities and deviations of the distributed clocks, which are not acceptable. For this application a bypass clock instead of the boundary clock is proposed as an enhancement of the IEEE-1588 standard. The effectiveness of this extension to be evaluated by simulation technique.
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Patent•
02 Jun 2011TL;DR: In this article, a system and method for synchronizing clocks across a packet-switched network eliminates wander accumulation to enable precision clock distribution across a large network, where each clock regenerator stage receives a grand clock error message from the previous stage, updates this error message with its own stage clock error, and then transmits the updated grand clock errors to the next stage.
Abstract: A system and method for synchronizing clocks across a packet-switched network eliminates wander accumulation to enable precision clock distribution across a large network. In addition to standard Precision Time Protocol (PTP) synchronization messages or similar time synchronization messages, each clock regenerator stage receives a grand clock error message from the previous stage, updates this error message with its own stage clock error, and then transmits the updated grand clock error to the next stage. This enables the synchronization algorithm to compensate for the error of the previous stage, effectively locking each clock regenerator stage to the grand master clock directly.
10 citations
Patent•
20 Jan 2011
TL;DR: In this paper, a portable articulated arm coordinate measuring machine including a manually positionable articulated arm portion having opposed first and second ends, the arm portion including a plurality of connected arm segments, each of the arm segments including at least one position transducer for producing position signals, a measurement device attached to the first end of the articulated arm coordinating measuring machine, an electronic circuit for receiving the position signals from the transducers and for providing data corresponding to a position of the measurement device, a base coupled to the second end, an upper mount portion disposed on the base, a lower mount
Abstract: Exemplary embodiments include a portable articulated arm coordinate measuring machine including a manually positionable articulated arm portion having opposed first and second ends, the arm portion including a plurality of connected arm segments, each of the arm segments including at least one position transducer for producing position signals, a measurement device attached to the first end of the articulated arm coordinate measuring machine, an electronic circuit for receiving the position signals from the transducers and for providing data corresponding to a position of the measurement device, a base coupled to the second end, an upper mount portion disposed on the base, a lower mount portion fixed to a mounting structure and configured to repeatably connect to the upper mount portion and an electronic identification system configured to send identifier information identifying the lower mount portion to the electronic circuit.
10 citations
05 May 2009
TL;DR: A probabilistic state-space model which quantifies the uncertainties and represents the relation between system variables is presented and the performance of this approach is verified by numerical results.
Abstract: Precision Time Protocol (PTP) synchronizes clocks of networked elements by exchanging messages containing precise time-stamps. A master clock is carefully chosen to provide the reference clock to the rest elements in the network, called slaves. Using the time-stamps, slave element learns the relation between its own clock and the master clock so that it can synchronize its time to the reference time. Uncertainties, e.g., random stamping and quantization errors, affect the synchronization precision. This paper presents a probabilistic state-space model which quantifies the uncertainties and represents the relation between system variables. Estimation of hidden variables, i.e. the system states, is carried out by using Kalman filter. The performance of this approach is verified by numerical results.
9 citations
22 Sep 2009
TL;DR: Fieldbus based automation solutions are widely accepted in industrial applications and the number of Profibus nodes is growing every year with more than 5 millions nodes.
Abstract: Fieldbus based automation solutions are widely accepted in industrial applications. In the last twenty years the number of Profibus nodes is growing every year with more than 5 millions nodes.
9 citations
TL;DR: The proposed method provides microseconds scale accuracy, which is applicable for trace events with nanosecond timestamp granularity, and does not require adding new network traffic, using the send and receive time of existing traffic.
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.
8 citations
References
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01 Jan 2003
TL;DR: OMNeT++ is fully programmable and modular, and it was designed from the ground up to support modeling very large networks built from reusable model components.
Abstract: The paper introduces OMNeT++, a C++-based discrete event simulation package primarily targeted at simulating computer networks and other distributed systems. OMNeT++ is fully programmable and modular, and it was designed from the ground up to support modeling very large networks built from reusable model components. Large emphasis was placed also on easy traceability and debuggability of simulation models: one can execute the simulation under a powerful graphical user interface, which makes the internals of a simulation model fully visible to the person running the simulation: it displays the network graphics, animates the message flow and lets the user peek into objects and variables within the model. These features make OMNeT++ a good candidate for both research and educational purposes. The OMNeT++ simulation engine can be easily embedded into larger applications. OMNeT++ is opensource, free for non-profit use, and it has a fairly large user
2,316 citations
TL;DR: The NTP synchronization system is described, along with performance data which show that timekeeping accuracy throughout most portions of the Internet can be ordinarily maintained to within a few milliseconds, even in cases of failure or disruption of clocks, time servers, or networks.
Abstract: The network time protocol (NTP), which is designed to distribute time information in a large, diverse system, is described. It uses a symmetric architecture in which a distributed subnet of time servers operating in a self-organizing, hierarchical configuration synchronizes local clocks within the subnet and to national time standards via wire, radio, or calibrated atomic clock. The servers can also redistribute time information within a network via local routing algorithms and time daemons. The NTP synchronization system, which has been in regular operation in the Internet for the last several years, is described, along with performance data which show that timekeeping accuracy throughout most portions of the Internet can be ordinarily maintained to within a few milliseconds, even in cases of failure or disruption of clocks, time servers, or networks. >
2,114 citations
"Enhancements to the time synchroniz..." refers background or methods in this paper
...The effectiveness of this extension will be evaluated by simulation technique....
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...This due to a decrease in price provoked by the office Ethernet market, high bandwidth, switching technology [3], priority features [4], full duplex operation [2], availability of Ethernet bridges as well as Ethernet-enabled products fulfilling industrial environmental requirements (e.g. [15])....
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27 Sep 2004
TL;DR: A protocol is provided in this standard that enables precise synchronization of clocks in measurement and control systems implemented with technologies such as network communication, local computing, and distributed objects.
Abstract: A protocol is provided in this standard that enables precise synchronization of clocks in measurement and control systems implemented with technologies such as network communication, local computing, and distributed objects. The protocol is applicable to systems communicating via packet networks. Heterogeneous systems are enabled that include clocks of various inherent precision, resolution, and stability to synchronize. System-wide synchronization accuracy and precision in the sub-microsecond range are supported with minimal network and local clock computing resources. Simple systems are installed and operated without requiring the management attention of users because the default behavior of the protocol allows for it.
1,428 citations
05 Dec 2002
TL;DR: This paper discusses the major features and design objectives of the IEEE-1588 standard, designed to serve the clock synchronization needs of industrial systems, and recent performance results of prototype implementations of this standard in an Ethernet environment are presented.
Abstract: This paper discusses the major features and design objectives of the IEEE-1588 standard. Recent performance results of prototype implementations of this standard in an Ethernet environment are presented. Potential areas of application of this standard are outlined.
1,112 citations
01 Apr 1994
TL;DR: In this article, the authors describe a series of incremental improvements in system hardware and software which result in significantly better accuracy and stability, especially in primary time servers directly synchronized to radio or satellite time services.
Abstract: This paper builds on previous work involving the Network Time Protocol, which is used to synchronize computer clocks in the Internet. It describes a series of incremental improvements in system hardware and software which result in significantly better accuracy and stability, especially in primary time servers directly synchronized to radio or satellite time services. These improvements include novel interfacing techniques and operating system features. The goal in this effort is to improve the synchronization accuracy for fast computers and networks from the tens of milliseconds regime of the present technology to the submillisecond regime of the future.In order to assess how well these improvements work, a series of experiments is described in which the error contributions of various modern Unix system hardware and software components are calibrated. These experiments define the accuracy and stability expectations of the computer clock and establish its design parameters with respect to time and frequency error tolerances. The paper concludes that submillisecond accuracies are indeed practical, but that further improvements will be possible only through the use of temperature-compensated local clock oscillators.
227 citations