Experimental Characterization of Uncertainty Sources in a Software-Only Synchronization System.

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Title: Experimental Characterization of Uncertainty Sources in a Software-Only Synchronization System.
Authors: Ferrari, Paolo1, Flammini, Alessandra1, Rinaldi, Stefano1, Bondavalli, Andrea2, Brancati, Francesco2
Source: IEEE Transactions on Instrumentation & Measurement. May2012, Vol. 61 Issue 5, p1512-1521. 10p.
Subjects: Synchronization software, Network Time Protocol (Computer network protocol), Global Positioning System, Timestamps, Internet protocols, Quartz crystals
Abstract: Over the past few decades, centralized computing systems have been replaced by decentralized systems, consisting of simple nodes interconnected by a communication network. The time reference of the distributed nodes must be synchronized in order to be able to coordinate the operation or compare the data collected by the different nodes. Several synchronization protocols have been developed to be used instead of global positioning system or dedicated synchronization systems. For example, the network time protocol (NTP) is a very popular synchronization protocol used to synchronize computers over wide area networks, like the Internet. In addition, IEEE 1588, a synchronization protocol dedicated to high-performance synchronization in local networks, was recently established. However, submicroseconds synchronization can be obtained only using dedicated hardware devices, thereby increasing the cost of each node. For these reasons, PTP software-only implementations are quite common in real systems, with a resulting synchronization uncertainty varying from a few to hundreds of microseconds and quite burdensome to estimate or measure. The work presented in this paper focuses on the analysis of the major uncertainty contributions in a software-only implementation. Particularly, a careful analysis of timestamp mechanism and time management in a PC platform is carried out. In addition, a method for the experimental evaluation of uncertainty contributions is proposed. A test case based on a software implementation of the IEEE 1588 (the so-called PTPd) is presented. The experimental tests presented in the paper highlight that the main uncertainty source of a software-only synchronization approach is the timestamp method. Timestamping accuracy can be affected by the computational load of the node itself: in normal conditions, the maximum uncertainty introduced by the timestamp mechanism is in the order of 10 \mu\s, but in case of high computational load, it can raise up to 224 \mu\s. [ABSTRACT FROM AUTHOR]
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  Data: Experimental Characterization of Uncertainty Sources in a Software-Only Synchronization System.
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  Data: <searchLink fieldCode="DE" term="%22Synchronization+software%22">Synchronization software</searchLink><br /><searchLink fieldCode="DE" term="%22Network+Time+Protocol+%28Computer+network+protocol%29%22">Network Time Protocol (Computer network protocol)</searchLink><br /><searchLink fieldCode="DE" term="%22Global+Positioning+System%22">Global Positioning System</searchLink><br /><searchLink fieldCode="DE" term="%22Timestamps%22">Timestamps</searchLink><br /><searchLink fieldCode="DE" term="%22Internet+protocols%22">Internet protocols</searchLink><br /><searchLink fieldCode="DE" term="%22Quartz+crystals%22">Quartz crystals</searchLink>
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  Data: Over the past few decades, centralized computing systems have been replaced by decentralized systems, consisting of simple nodes interconnected by a communication network. The time reference of the distributed nodes must be synchronized in order to be able to coordinate the operation or compare the data collected by the different nodes. Several synchronization protocols have been developed to be used instead of global positioning system or dedicated synchronization systems. For example, the network time protocol (NTP) is a very popular synchronization protocol used to synchronize computers over wide area networks, like the Internet. In addition, IEEE 1588, a synchronization protocol dedicated to high-performance synchronization in local networks, was recently established. However, submicroseconds synchronization can be obtained only using dedicated hardware devices, thereby increasing the cost of each node. For these reasons, PTP software-only implementations are quite common in real systems, with a resulting synchronization uncertainty varying from a few to hundreds of microseconds and quite burdensome to estimate or measure. The work presented in this paper focuses on the analysis of the major uncertainty contributions in a software-only implementation. Particularly, a careful analysis of timestamp mechanism and time management in a PC platform is carried out. In addition, a method for the experimental evaluation of uncertainty contributions is proposed. A test case based on a software implementation of the IEEE 1588 (the so-called PTPd) is presented. The experimental tests presented in the paper highlight that the main uncertainty source of a software-only synchronization approach is the timestamp method. Timestamping accuracy can be affected by the computational load of the node itself: in normal conditions, the maximum uncertainty introduced by the timestamp mechanism is in the order of 10 \mu\s, but in case of high computational load, it can raise up to 224 \mu\s. [ABSTRACT FROM AUTHOR]
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  Label:
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  Data: <i>Copyright of IEEE Transactions on Instrumentation & Measurement is the property of IEEE and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1109/TIM.2011.2180974
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        Text: English
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      – SubjectFull: Timestamps
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        Type: general
      – SubjectFull: Quartz crystals
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      – TitleFull: Experimental Characterization of Uncertainty Sources in a Software-Only Synchronization System.
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              Text: May2012
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