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Precision Clock Synchronization for Measurement Control and Communication (ISPCS), 2011 International IEEE Symposium on

Date 12-16 Sept. 2011

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  • [Front cover]

    Page(s): c1
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  • [Copyright notice]

    Page(s): ii
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  • Table of contents

    Page(s): iii - vi
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  • [Front matter]

    Page(s): vii - xiv
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  • Applying IEEE 1588 to packet radio trilateration

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1193 KB) |  | HTML iconHTML  

    There are several applications for position location that require a solution that minimizes size and power. In the case of planetary navigation, these constraints are critical due to the cost of deployment. This paper describes the analysis, design, and prototyping of a system that takes advantage of a common time-base provided by IEEE 1588 Precision Time Protocol (PTP) to use minimal processing algorithms and processing resources. View full abstract»

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  • Timing and synchronization for Quasi-Real-Time systems using IEEE 1588v2 over Ethernet

    Page(s): 7 - 12
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    Ethernet and IEEE 1588 are continuing to emerge in a wide range of industries. Increasingly, they are replacing industry-specific interconnects, delivering performance and cost efficiencies. Initiatives including Industrial Ethernet, IEC 61850, and LXI are all adopting commercial off- the-shelf technologies to achieve broader communications at far lower costs. However, significant investments that are warranted for large automation systems become prohibitively expensive for a diverse set of less, ambitious Quasi-Real-Time (QRT) applications that also require distributed communications and timing. This paper proposes an approach to address the communications and timing/synchronization requirements for QRT systems, characterized by simple and low-cost devices interconnected and synchronized over a real-time network. To achieve the aggressive cost targets, a highly integrated attachment device is introduced that integrates Ethernet communications, IEEE 1588v2 distributed synchronization, and precision I/O for local synchronization in a single, energy efficient device. Systems issues are also raised affecting the applicability for applications that can exploit a QRT network. View full abstract»

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  • Towards high accuracy in IEEE 802.11 based clock synchronization using PTP

    Page(s): 13 - 18
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB) |  | HTML iconHTML  

    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. View full abstract»

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  • Compensation of asymmetrical latency for ethernet clock synchronization

    Page(s): 19 - 24
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    Clock synchronization has become an indispensable service in most distributed systems as it allows to sort events on a common time scale and coordinate collaborative actions.With the demand for even higher synchronization accuracy, new challenges and barriers have to be tackled to fulfill these requirements. One of them, the inevitable signal propagation time between the devices, is compensated in many state-of-the-art synchronization protocols by round-trip measurements, neglecting any form of delay asymmetry of the communication link. In this paper, we analyze the impact of asymmetry in networks based on the physical layer of copper-based Ethernet and compare different approaches on how to mitigate the impact of asymmetry. We propose a non-invasive system performing asymmetry measurements on a link basis and show that such a system can integrate into existing synchronization solutions. View full abstract»

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  • White rabbit: a PTP application for robust sub-nanosecond synchronization

    Page(s): 25 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1000 KB) |  | HTML iconHTML  

    This article describes time distribution in a White Rabbit Network. We start by presenting a short overview of the White Rabbit project explaining its requirements to highlight the importance of the timing aspects of the system. We then introduce the technologies used to achieve high clock accuracy, stability and resilience in all the components of the network. In particular, the choice of the IEEE 1588-2008 (PTP) and Synchronous Ethernet standards are explained. In order to accommodate hardware-supported mechanisms to increase PTP synchronization accuracy, we introduce the White Rabbit extension to PTP (WRPTP). The hardware used to supportWRPTP is presented.Measured results of WRPTP performance demonstrate sub-nanosecond accuracy over a 5km fiber optic link with a precision below 10ps and a reduced PTP-message exchange rate. Tests of the implementation show full compatibility with existing PTP gear. View full abstract»

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  • Dual and hybrid PTP modules

    Page(s): 31 - 37
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (827 KB) |  | HTML iconHTML  

    The IEEE 1588-2008 standard [1] introduces and specifies Boundary Clock (BC) and Transparent Clock (TC) concepts in order to address stringent time distribution requirements (e.g. 1 μs accuracy for the end application) across a communication network. Both concepts present different strengths and weaknesses which are generally used as arguments to oppose one against the other. This paper, on the contrary, is advocating for the implementation of both functionalities on the same network node with regards to the great commonalities and complementarities between them. Going further on this complementary approach, this contribution proposes a hybrid module aiming at combining different advantages offered respectively by BC and TC concepts. View full abstract»

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  • Time synchronization security using IPsec and MACsec

    Page(s): 38 - 43
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    The wide deployment of the IEEE 1588 Precision Time Protocol (PTP) raises significant security concerns; its quick assimilation has outrun security standardization efforts. In the absence of a standard security solution for PTP, several different alternatives have been suggested as a means to fill this vacuum using existing off-the-shelf security protocols. In this paper, we analyze PTP security solutions using two such protocols; IPsec and MACsec. We characterize the common deployment scenarios for PTP using these protocols, and then present a security threat analysis under these scenarios. View full abstract»

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  • Validation and verification of IEEE 1588 Annex K

    Page(s): 44 - 49
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    The Precision Time Protocol (PTP) specified by IEEE 1588 contains a security extension to properly protect the exchanged information. The purpose of this extension is to detect manipulation and illegitimate replay of PTP messages and consequently prevent malicious attacks. To gain confidence in certain implementations this article presents a basic test suite to validate and verify the IEEE 1588 security extension. Based on an analysis of the security functionality a test setup and basic test cases are presented that allow to test Targets Of Evaluation (TOE) - ordinary as well as transparent clocks - and being able to give evidence about the correct security functionality. Outcome is a set of 13 test cases that cover all aspects of PTP security, namely message protection, mutual authentication and management of security associations. View full abstract»

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  • High-precision UWB-based timestamping

    Page(s): 50 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (765 KB) |  | HTML iconHTML  

    The work presented in this paper is related with time synchronization for wireless networks. In particular, it is focused on the proposal and experimental evaluation of a low-cost and high precision timestamping technique based on Ultra Wide Band (UWB) signalling. In recent years, the use of such systems has gained an increasing success thanks to their robustness to interferers and multipath. In this paper a new hybrid wireless node is proposed; a traditional IEEE802.15.4 radio, the reference physical layer for wireless sensor networks, is supported by an UWB transceiver. The former is used for communication purposes and allows to preserve compatibility with already installed infrastructures/networks; the latter is used for time of arrival estimation. Hardware prototypes have been realized and experimental tests have shown a sub-nanosecond accuracy. A comparison with commercial solutions has shown a performance improvement with respect to conventional approaches. View full abstract»

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  • Characterizing grandmaster, transparent, and boundary clocks with a precision packet probe and packet metrics

    Page(s): 56 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1167 KB) |  | HTML iconHTML  

    The IEEE 1588 packet probe has proved to be an effective tool for the measurement and analysis of network packet delay variation and latency. As more and more IEEE 1588 equipment is designed and deployed in the service of telecommunications networks and for other applications, in some cases with on-path support provided by boundary or transparent clocks, it has become important to be able to characterize this equipment. In many cases the packets themselves are the only timing signal available for study. Thus the packet probe is an essential tool for characterizing this equipment. Likewise, the same metrics developed for the analysis of network packet delay variation can be employed for equipment characterization. This paper, drawing on measurements of commercial equipment, describes how a packet probe along with traditional stability metrics and recently developed packet metrics can be used to characterize IEEE 1588 grandmaster clocks, boundary clocks, and transparent clocks. View full abstract»

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  • Transparent Clocks vs. Enterprise Ethernet switches

    Page(s): 62 - 68
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (642 KB) |  | HTML iconHTML  

    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. View full abstract»

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  • Time distribution in IPv6 Wireless Sensor Networks

    Page(s): 69 - 74
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    In the last years, Wireless Sensor Networks experienced a great success in the research community and also the interest of the industrial world seems increasing, as demonstrated by the definition of several standards (e.g. WirelessHART and ISA100.11a). Up to now, network robustness and optimization of the power consumption are the key point of a sensors network. However, the recent technology improvements offer a plenty of processing power and, in this scenario, some background aspects (e.g. advanced networking and time synchronization) cannot be ignored. This paper focuses its attention on synchronization on Wireless Sensor Network based on IPv6 protocol. The integration of IEEE 1588 protocol into this scenario has been analyzed. The synchronization stack has been implemented over a performing platform, which achieves a timestamping accuracy in the order of ±500 ns. However, the synchronization capabilities of the overall system is in the order of 1 ms. View full abstract»

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  • Time synchronization performance of desktop computers

    Page(s): 75 - 80
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (645 KB) |  | HTML iconHTML  

    Time synchronization is a vital requirement for various applications. Especially the synchronization of desktop computers to the Coordinated Universal Time (UTC) yields numerous use cases, such as distributed measurements. Several solutions address this need, at different levels of price and accuracy. In this work we evaluate on the achievable precision in time synchronization of a desktop PC, for example, assisted by a low-budget GPS receiver. This is achieved by a novel measurement setup, which is comparing the software synchronized internal clock of the PC to a rubidium frequency standard. Our results show, that the synchronization offsets of the software clocks of all tested PCs have positive mean (time lag) in the order of 10 μs. The respective standard deviation is typically an order of magnitude lower. Thereby the unknown interrupt latency is the limiting factor for the accuracy. With this work we show that today (2011) 10 μs of precision can be achieve at very low cost. View full abstract»

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  • An isochronous medium access for real-time wireless communications in industrial automation systems - A use case for wireless clock synchronization

    Page(s): 81 - 86
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    Wireless technologies are increasingly deployed in factory automation systems, because they are able to provide several advantages, e. g., a higher level of mobility, more flexibility, and at the same time causing lower costs. However, the requirements of industrial applications in terms of real-time communication can not be satisfied by existing wireless technologies, such as IEEE 802.11Wireless Local Area Networks (WLANs). This is due to their unpredictable behaviour and the introduction of delays beyond acceptable bounds, mainly caused by a non-deterministic medium access. Hence, the proposed wireless communication system provides real-time communication services based on the IEEE 802.11 protocol family. In this paper we present a new isochronous medium access control mechanism, called IsoMAC. The paper addresses IsoMAC and shows how, in combination with a suitable wireless clock synchronization, IsoMAC is able to satisfy the typical constraints of soft real-time flows found on the factory floor. A simulation case study is provided that shows the achievable update times of the proposed combination. View full abstract»

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  • Synchronizing the Linux system time to a PTP hardware clock

    Page(s): 87 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (767 KB) |  | HTML iconHTML  

    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. View full abstract»

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  • Temporal synchronization in multi-sensor fusion for future driver assistance systems

    Page(s): 93 - 98
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (826 KB) |  | HTML iconHTML  

    A new approach to precise timestamping and temporal synchronization in a multi-sensor setup is presented. Modern driver assistance systems use an increasing amount of different sensors that do not provide the exact timestamps of the measurements, nor the period of time between two measurements. This paper describes a method to determine these timestamps up to millisecond accuracy. Possible drifts of the internal sensor clocks are taken into account. In addition, a frequent problem are lost measurements that lead to large errors in the timestamping. These framedrops are detected reliably and handled adequately via the method at hand. Finally a method to evaluate the performance of the whole timestamping procedure is described and real-world results are presented. View full abstract»

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

    Page(s): 99 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB) |  | HTML iconHTML  

    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. View full abstract»

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  • Simulations of a chain of Telecom Boundary Clocks combined with Synchronous Ethernet for phase/time transfer

    Page(s): 105 - 113
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    This paper describes the use of Boundary Clocks for clock distribution (phase/time transfer) in telecom networks. The technology is primarily used to meet synchronization requirements of mobile systems such as TD-SCDMA and LTE, and to reduce the use of and dependency on GPS systems deployed in base stations. We describe the most important functions of a Telecom Boundary Clock, which are under discussion at ITU-T. We then present a network reference model and simulation model based on IEEE1588 and Synchronous Ethernet. The results indicate that it is possible to transfer phase/time in a telecom network for meeting the microsecond-level requirement of various mobile systems. The paper also discusses some of the ongoing activities in standardization bodies so that IEEE1588 can be used as a technology in telecom networks. View full abstract»

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  • A packet filtering mechanism with a packet delay distribution estimation function for IEEE 1588 time synchronization in a congested network

    Page(s): 114 - 119
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (971 KB) |  | HTML iconHTML  

    This paper presents a packet filtering mechanism by using packet delay distribution estimation for improving the clock stability of time synchronization with IEEE 1588. We study a packet delay distribution estimation method by using a dedicated probing packet, and discuss the applicability of the estimation method for the clock control mechanism in IEEE 1588 slave nodes. Numerical simulations show that the packet delay distribution estimation method is effective for packet filtering in heavily congested networks. View full abstract»

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  • Robustness to SYNC packets loss in network synchronization

    Page(s): 120 - 125
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (895 KB) |  | HTML iconHTML  

    Several factors may impact on the achievable performances of a synchronization system: among them, the accuracy of drift and offset estimates, the short and long term stability of the unregulated clock, the rate at which timing information are exchanged, the probability of losing protocol messages for a given period of time and so on. Therefore, when a synchronization scheme is considered, it is very important to also specify its robustness to possible malfunctions. In this paper the behaviour of synchronization mechanisms will be studied in correspondence to a synchronization loss. We shall analyse how clock instability and other factors, such as timestamp uncertainty and the particular implementation of a servo clock, may strongly affect the performances of a synchronization protocol. Finally, an accurate study based on the effect of measurement uncertainty will be reported to evaluate the robustness of a given synchronization mechanism with respect to an information loss. View full abstract»

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

    Page(s): 126 - 131
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    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. View full abstract»

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