Software and hardware prototypes of the IEEE 1588 precision time protocol on wireless LAN
21 Nov 2005-pp 1-6
TL;DR: The design and implementation of two IEEE 1588 prototypes for wireless LAN (WLAN) are presented and the results achieved are fully comparable to those achieved with wired LAN implementations.
Abstract: IEEE 1588 is a standard for precise clock synchronization for networked measurement and control systems in LAN environment. This paper presents the design and implementation of two IEEE 1588 prototypes for wireless LAN (WLAN). The first one is implemented using a Linux PC platform and a standard IEEE 802.11 WLAN with modifications to the network device driver. The second prototype is implemented using an embedded WLAN development board that implements the synchronization functionality using an embedded processor with programmable logic device (PLD) circuits. The measured results show that 1.1 ns average clock offset can be reached on HW based implementation, while Linux PC network driver enables 660 ns with a standard WLAN. Although WLAN is an extremely difficult environment for the synchronization, the results achieved with the prototype are fully comparable to those achieved with wired LAN implementations
Citations
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TL;DR: Three synchronization methods based on NTP (network time protocol), on GPS (global positioning system), and on IEEE 1588 standard are described and compared showing the advantages and disadvantages of the analyzed methods.
Abstract: Nowadays, the evaluation of performance measurement in computer networks is an important issue. To ensure the quality of service of the network communication, one of the most important network performance parameters is the one-way delay (OWD). For accurate OWD estimation, it is essential to consider some parameters that can influence the measure, such as the operating system and, in particular, the threads, which are concurrent with the measurement application. Moreover, OWD estimation is not an easy task, because it can be affected by synchronization uncertainties. This paper aims to review the different solutions proposed in the scientific literature for OWD measurement. These solutions adopt different methods to guarantee a reasonable clock synchronization based on the Network Time Protocol, the Global Positioning System, and the IEEE 1588 Standard. These different approaches are critically reviewed, showing their advantages and disadvantages.
116 citations
Cites background or methods or result from "Software and hardware prototypes of..."
...However, this requires relatively expensive GPS receivers, the appropriate antennas on the roof, and the necessary cabling [20]....
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...These methods are quite common in LANs or on the Internet and allow accuracies in the millisecond range [20]....
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...The results reported in [20] show that synchronization accuracy obtained by PLD is almost three decades better than that with Linux PC implementation....
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...The design and implementation of two IEEE 1588 prototypes for wireless LAN (WLAN) are presented in [20]....
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TL;DR: This survey looks into the details of synchronization over IEEE 802.11 with a particular focus on the infrastructure mode which is most relevant for industrial use cases and highlights the different parameters which affect the performance of clock synchronization over WLAN and compares the performances of existing synchronization methods to analyze their shortcomings.
Abstract: Just like Ethernet before, IEEE 802.11 is now transcending the borders of its usage from the office environment toward real-time communication on the factory floor. However, similar to Ethernet, the availability of synchronized clocks to coordinate and control communication and distributed real-time services is not a built-in feature in WLAN. Over the years, this has led to the design and use of a wide variety of customized protocols with varying complexity and precision, both for wired and wireless networks, in accordance with the increasingly demanding requirements from real-time applications. This survey looks into the details of synchronization over IEEE 802.11 with a particular focus on the infrastructure mode which is most relevant for industrial use cases. It highlights the different parameters which affect the performance of clock synchronization over WLAN and compares the performance of existing synchronization methods to analyze their shortcomings. Finally, it identifies new trends and directions for future research as well as features for wireless clock synchronization which will be required by the applications in the near future.
108 citations
TL;DR: For the first time, the individual sources of delay and jitter are investigated for an IEEE 802.11 wireless local area network (WLAN) synchronization system using the IEEE 1588 protocol and software timestamps and results show that with optimal error compensation, a similar synchronization performance as software-based synchronization in Ethernet networks can be achieved.
Abstract: In distributed systems, clock synchronization performance is hampered by delays and jitter accumulated not only in the network, but also in the timestamping procedures of the devices being synchronized. This is particularly critical in software timestamp-based synchronization where both software- and hardware-related sources contribute to this behavior. Usually, these synchronization impairments are collapsed into a black-box performance figure without quantifying the impact of each individual source, which obscures the picture and reduces the possibility to find optimized remedies. In this study, for the first time, the individual sources of delay and jitter are investigated for an IEEE 802.11 wireless local area network (WLAN) synchronization system using the IEEE 1588 protocol and software timestamps. Novel measurement techniques are proposed to quantify the hardware- and software-related delay and jitter mechanisms. It is shown that the delays and their associated jitter originate from both the WLAN chipset and the host computer. Moreover, the delay from the chipset cannot be considered symmetric and any such assumption inevitably leads to a residual offset, and thus to synchronization inaccuracy. Therefore, a calibration-based approach is proposed to compensate for these delays and to improve the performance of WLAN synchronization. Experimental results show that with optimal error compensation, a similar synchronization performance as software-based synchronization in Ethernet networks can be achieved.
75 citations
Cites background from "Software and hardware prototypes of..."
...Owing to the lack of knowledge about the underlying hardware in software timestamp-based synchronization, it is common to treat the system as a black-box, draw timestamps inside the driver or at a higher layer, and focus only on the final synchronization performance as shown in [11] and [12]....
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03 Dec 2010
TL;DR: A passive synchronization algorithm that can significantly reduce timing error versus naively time-stamping sensor data when it arrives at the host and is passive in the sense that the algorithm requires no special cooperation from the sensor.
Abstract: Knowing the time at which sensors acquired data is critical to the proper processing and interpretation of that data, particularly for mobile robots attempting to project sensor data into a consistent coordinate frame. Unfortunately, many popular commercial sensors provide no support for synchronization, rendering conventional synchronization algorithms useless. In this paper, we describe a passive synchronization algorithm that can significantly reduce timing error versus naively time-stamping sensor data when it arrives at the host. It is passive in the sense that the algorithm requires no special cooperation from the sensor. Our method estimates the timing jitter induced by hosts, and thus does not require a real-time operating system. We rigorously derive and characterize the method, proving that it can only improve upon the synchronization accuracy of the standard approach.
62 citations
Cites background from "Software and hardware prototypes of..."
...11 wireless ethernet [9] and can provide sub-microsecond synchronization....
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29 Aug 2009
TL;DR: The result established a method for nodes in a network to maintain their clocks to within a 200 nanosecond offset from the reference clock of a master node, which provides compatibility between heterogeneous systems in WSNs.
Abstract: Wireless sensor networks are evolving from relatively undemanding applications to applications which have stronger requirements. The coordination of distributed entities and events requires time synchronization. Although a number of methods have been studied for WSNs, some applications require high precision time synchronization. Precision time synchronization enables a variety of extensions of applications. The IEEE 1588 precision time protocol (PTP) provides a standard method to synchronize devices in a network with sub-microsecond precision. This paper deals with precision time synchronization using IEEE 1588 over wireless sensor networks. Precision time synchronization using IEEE 1588 provides compatibility between heterogeneous systems in WSNs. This paper also presents experiments and performance evaluation of precision time synchronization in WSNs. Our result established a method for nodes in a network to maintain their clocks to within a 200 nanosecond offset from the reference clock of a master node.
56 citations
Cites background from "Software and hardware prototypes of..."
...The PTP specially addresses spatially localized networks, maintaining microsecond to sub-microsecond accuracy, and it is administration free, and accessible for both high-end and lowend devices between heterogeneous systems....
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References
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01 Jan 1996
2,375 citations
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
TL;DR: It is shown that sub-microsecond synchronization accuracy is readily achieved using the IEEE 1588 protocol and some of the ways in which this common sense of time may be exploited in time-based measurement and control applications are suggested.
Abstract: We outline three architectures for establishing system timing used in both the general computing environment and in the more specialized environment of test, measurement, and industrial control. Increasingly tight synchronization requirements and the trend to more distributed and peer-to-peer applications have led to the development of the IEEE 1588 standard as a means of establishing a precise common sense of time in the test, measurement, and industrial control environment. We suggest some of the ways in which this common sense of time may be exploited in time-based measurement and control applications. It is shown that sub-microsecond synchronization accuracy is readily achieved using the protocol.
53 citations
"Software and hardware prototypes of..." refers methods in this paper
...An IEEE 1588 prototype with hardware based timestamping has been presented in [4]....
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01 Aug 2004
TL;DR: The design and implementation of an IEEE 1588 PC software prototype for Wireless LANs (WLAN) is presented and accuracy is improved using two new developed methods for outbound latency estimation.
Abstract: IEEE 1588 is a new standard for precise clock synchronization for networked measurement and control systems in LAN environment. This paper presents the design and implementation of an IEEE 1588 PC software prototype for Wireless LANs (WLAN). Accuracy is improved using two new developed methods for outbound latency estimation. In addition, an algorithm for adjusting the local clock is presented. The achieved accuracy is measured and compared between WLAN and fixed LAN environments. The results show that 2.8 μs average clock offset can be reached on WLAN, while wired Ethernet connection enables 2.5 μs.
34 citations
"Software and hardware prototypes of..." refers methods in this paper
...However, in [3] we presented a method called external echo that was used to completely remove the inaccuracy caused by AP....
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...For comparison, it also contains the previous Windows software measurements reported in [3]....
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...Our earlier research [3] reports the performance of software based IEEE 1588 prototype on Windows platform....
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...The algorithm used in the Windows SW prototype is described in [3]....
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