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.
Citations
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15 Sep 2004
TL;DR: This work presents the communication architecture and model for Profinet IO, which is an enhancement of the Profibus DP device model, and includes a more flexible control access of one or more IO controllers in parallel to one IO device.
Abstract: This work presents the communication architecture and model for Profinet IO that has been currently released by the Profibus User Organization Profinet IO provides the service definition and protocol specification for real time communication based on Ethernet, IP, and UDP for the field bus domain It defines services and protocols mainly for communication between IO controllers (eg a PLC) and IO devices (eg Remote IO) It Includes a QoS architecture for real time control and alarm messages taking precedence over parameter, diagnosis, or Infrastructure messages Including other TCP or UDP based protocols High message priorities In combination with a time division multiplexing approach with direct data link layer access provide short cycle times and low jitter The IO device model itself is an enhancement of the Profibus DP device model The enhancement includes a more flexible control access of one or more IO controllers in parallel to one IO device Furthermore, address parameters and levels are enhanced too The specification itself is according to IEC 61158 styles, which opens the possibility to be easily added in a new maintenance period of the standard
13 citations
TL;DR: A data-based predictive hybrid driven control (DPHDC) approach is presented for a class of networked systems compromising both computation and communication delays, packet dropouts, and disturbances.
Abstract: A data-based predictive hybrid driven control (DPHDC) approach is presented for a class of networked systems compromising both computation and communication delays, packet dropouts, and disturbances. First, network problems are classified in a generic way, which is used to design a network problem detector capable of detecting online current delays and packet dropouts. Second, a single-variable first-order proportional-integral based adaptive grey model [PIAGM(1,1)] is designed to predict future network problems, and to predict system disturbances. Third, a hybrid driven scheme integrated optimal small buffer (OSB) is constructed to allow the system to operate without any interrupts due to large delays or packet dropouts. Furthermore, the OSB size is online optimized using an adaptive grey fuzzy cognitive map technique. Forth, a prediction-based model-free adaptive controller is developed to compensate for network problems. The DPHDC stability is theoretically proved, while its effectiveness is demonstrated through a case study.
13 citations
Cites methods from "Enhancements to the time synchroniz..."
...For the synchronization of the clocks between the MCU and plant, the first delay between the MCU and plant, τ ca(1), is determined using the well-known IEEE 1588-based precition time protocol, timestamps, and the assumption that the forward and backward transport delay at the beginning of system operation is symmetric [32], [33]....
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24 Oct 2008
TL;DR: A simulation environment to evaluate coexistence of RTE protocols is introduced and some improvements to the PTP tracking algorithms to ease coexistence are proposed.
Abstract: This paper investigates Real-Time Ethernet (RTE) protocols for industrial applications and their clock synchronization performance. In fact, if different RTE protocols coexist on the same network sharing the same infrastructure, clock synchronization capabilities can be affected. This paper introduces a simulation environment to evaluate coexistence of RTE protocols. The proposed tool is described and validated by comparison with measurement data taken from real networks. Finally, simulation results are presented: the behavior of Ethernet/IP with IEEE1588-PTP, when it is transported over an isochronous PROFINET IO network, is shown and some improvements to the PTP tracking algorithms to ease coexistence are proposed.
13 citations
Cites background from "Enhancements to the time synchroniz..."
...Clearly, the infrastructure components are synchronized in order to change modality (PNIO Class 2/3 – rest of the traffic) in a coordinated way [9]....
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Patent•
30 Oct 2014TL;DR: In this paper, an EtherCAT control device and a factory automation system having the same are provided. But the authors focus on the control of the first slave according to a precision time protocol (PTP).
Abstract: An EtherCAT control device and a factory automation system having the same are provided. The EtherCAT control device includes a master including a dummy EtherCAT slave controller (ESC) and a first slave configured to communicate data with the master according to an EtherCAT protocol, such that the master synchronizes a timing with the first slave according to a precision time protocol (PTP) method using the dummy ESC.
12 citations
26 Jun 2007
TL;DR: An overview of the state-of-art of real-time sensor networks for industrial applications, problems and possible approaches to solve them are presented, with particular reference to methods and instrumentation for performance measurement.
Abstract: Industrial applications are moving from centralized architectures towards distributed ones, thanks to cost effectiveness, better flexibility, scalability, reliability and diagnostic functionalities. The use of sensors in industrial communications improves overall plant performance since sensor information can be used by several equipments and shared on the Web. A communication system suitable for computers and PLCs, that exchanges a large amount of data with soft real-time constrains, can be hardly adapted to sensors, especially to simple and low-cost ones. In fact, these devices typically require a cyclic, isochronous and hard realtime exchange of few data. For this reason, specific fieldbuses have been widely used to realize industrial sensor networks, while high-level industrial communication systems take advantage of Ethernet/Internet and. more recently, wireless technologies. In these years, Ethernet-based solutions that meet real-time operation requirements, called Real-Time Ethernet, are replacing traditional fieldbuses and research activities in real-time wireless sensor networking are growing. In this paper, following an overview of the state-of-art of real-time sensor networks for industrial applications, problems and possible approaches to solve them are presented, with particular reference to methods and instrumentation for performance measurement.
12 citations
Cites background from "Enhancements to the time synchroniz..."
...In addition, in industrial plants, star topologies are considered unsuitable, so if many switches are cascaded [32], propagation delay of a frame is asymmetric and IEEE1588 could yield to considerable estimation errors....
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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