Clock synchronization Research Papers - Academia.edu (original) (raw)

Frontiers of technology now need synchronization between remote clocks to an accuracy of about a nanosecond. Rate changes a r i s i i from the velocity and gravitational potential of a transported clock used for synchronization of a network must be accounted for. In addition, one cannot assume that the carth is an inertial frame, i.e., not spinning. If classical Einstein synchronization is used, where from the midpoint between clocks at A and at B, one simultaneously sends light pulses to A and B to synchronize them, two problems arise. First, the synchronization process will not be transitive; i.e., if A is synchronized with B and B with C. then A wiU not necessarily be synchronized with C. Second, starting at a point on the equator and transporting a portable clock eastward (westward), while establishing a synchronized time end on the way, will result in a discontinuity upon returning to the original point of about -200 ns (+200 ns); minus (-) means that the portable clock will be late. This paper will discuss the construction of a coordinate clock network on the earth's surface which does not have these problems; i.e., synchronization is transitive, and there i s no discontinuity. This may be done by adjusting clocks to read coordinate time on an underlying nonrotating local inertial frame. The theoretical and practical implications of setting up such a coordinate clock network using either electromagnetic signals (e.g., laser, Loran-C) or portable clocks will bc discussed. It will be shown how this network may be applied in making UTC or any other global scale more useful for statwf-the-art navigation and communication systems.

- by
- •
- Multidisciplinary, Communication System, Clock synchronization, Earth Rotation

Many distributed applications require a clock synchronization service. We have previously proposed a clock synchronization service for the Controller Area Network (CAN), which we have claimed to provide highly synchronized clocks even in the occurrence of faults in the system. In this paper we substantiate this claim by providing a formal model and verification of our fault tolerant clock synchronization mechanism. We base our modeling and verification on timed automata theory as implemented by the model checking tool UPPAAL. In the modeling we introduce a novel technique for modeling drifting clocks. The verification shows that a precision in the order of 2 µs is guaranteed despite node's faults as well as consistent channel faults. It also shows that inconsistent channel faults may significantly worsen the achievable precision, but that this effect can be reduced by choosing a suitable resynchronization period.

- by Guillermo Rodriguez-navas and +1
- •
- Model Checking, Clock synchronization, Formal Verification, Fault Tolerant

The fundamental role of signal processing techniques was demonstrated
in the context of clock synchronization in WSNs. This
article explains many existing intuitive clock synchronization
protocols and gives some directions to the necessary ingredients
for devising an optimal estimator operating under an unconventional
environment. However, centralized signal processing
techniques can only help solving the problem of node-to-node
synchronization and possible ad hoc extensions to network-wide
synchronization. The next important step is the application of
decentralized signal processing techniques (e.g., distributed estimation
and detection) to the clock synchronization problem, and
this naturally results in desirable distributed clock synchronization
algorithms. Furthermore, distributed signal processing techniques
will reveal the optimal way of information passing, thus
saving unnecessary communication overhead.

This paper details on the design of OFDM receivers. Special attention is paid to the OFDM-specific receiver functions necessary to demodulate the received signal and deliver soft information to the outer receiver for decoding. In Part I of the paper, the effects of nonideal transmission conditions have been thoroughly analyzed. To show the impact of the synchronization algorithms-which are most critical in OFDM-on system performance and complexity we consider the design of a complete receiver consisting of symbol synchronization, carrier/sampling clock synchronization and channel estimation. The performance of the algorithms is analyzed and a qualitative estimate of the resulting complexity is given. This allows to draw conclusions concerning the achievable system performance under realistic complexity assumptions.

- by H. Meyr
- •
- Channel Estimation, Case Study, Clock synchronization, System performance

One of the missions of the North American Syn-chroPhasor Initiative (NASPI) is to create a robust, widely available and secure synchronized data measurement infrastructure, dubbed NASPInet, that will improve reliability of the power grid. Phasor Measurement Unit (PMU), a GPS clock synchronized measurement device capable of measuring the current and voltage phasors in the power grid, is the main measurement device that NASPInet envisions to support. While the dataflow, latency and to some extent security requirements for individual PMU applications that depend on the measurement infrastructure have been characterized, this work undertakes the challenge of characterizing the collective dataflow, latency and security requirements of the measurement infrastructure when using different network architectures and when multiple PMU applications simultaneously utilize NASPInet. For our analysis we focus on a case study where we model a scalable scenario in NASPInet for a part of the North American Power Grid, the western interconnect, using Network Simulator v2 (NS-2).

- by Ragib Hasan
- •
- Data Analysis, Synchronization, Global Positioning System, Security Requirements
- by E. Serpedin
- •
- Wireless Sensor Networks, Synchronization, Energy efficiency, Time Synchronization

Recently, seven single nucleotide polymorphisms (SNPs) of ARNTL, TIM and PER3 genes were found associated with affective temperaments in bipolar disorder patients. This study aimed to test whether a) the same associations appear in a non-clinical sample; b) the SNPs are related to other affective dimensions; c) the SNPs underpin the associations between chronotype and affective temperaments/dimensions. Three hundred thirty-eight university students completed the Temperament Scale of Memphis, Pisa, Paris and San Diego Auto-questionnaire, the Centre for Epidemiological Studies Depression Scale, the Perceived Stress Scale, the General Health Questionnaire, the Seasonal Pattern Assessment Questionnaire and the Composite Scale of Morningness. Seven SNPs of the ARNTL, TIM and PER3 genes were genotyped. According to nominal significance ARNTL rs7107287 was associated with a cyclothymic temperament, depressive and stress symptoms, general mental health and perceived negative impact of seasonality, while TIM rs10876890 was associated with a hyperthymic temperament and the TIM rs2291738 was associated with chronotype. Different SNPs were related to chronotype and affective temperaments/dimensions and therefore they seem to not underpin relationships between chronotype and affective dysfunction, i.e. in the present study eveningness was related to dysthymic, cyclothymic and irritable temperaments, more symptoms of depression, stress, worse mental health and a negative impact of seasonality, while morningness was related to hyperthymic temperament. The SNPs associations need further replication given that they did not achieve Bonferroni criteria of significance accounting for the number of polymorphisms considered and tests conducted.

- by Konrad S Jankowski
- •
- Chronobiology, Genetics, Psychology, Clinical Psychology

Clock discrepancies are troublesome in distributed systems and pose major difficulties. To avoid mistakes, the clocks of separate CPUs must be synced. This is to ensure that communication and resource sharing are as efficient as possible. As a result, the clocks must be constantly monitored and adjusted. Otherwise, the clocks drift apart. Clock skew causes a disparity in the time values of two clocks. Both of these issues must be solved in order to make effective use of distributed system characteristics. In this study, we briefly explored the features of distributed systems and its algorithms.

- by AMEY THAKUR and +1
- •
- Distributed Computing, Computer Networks, Clock synchronization

The paper addresses clock synchronization issues in a wireless sensor network used for vibration measurements in an industrial environment. After discussing the reasons for using Bluetooth technology in such a context, the paper identifies the synchronization requirements imposed on the sensor nodes clocks by the envisaged application and examines various clock synchronization algorithms, discussing their advantages and applicability to the context being investigated. The paper then proposes an original synchronization approach which exploits some peculiar Bluetooth features and discusses the performance obtained and concludes by outlining open issues to be addressed in future research.

- by Lucia Bello
- •
- Wireless Sensor Networks, Synchronization, Sensor Arrays, Clock synchronization

Precise time synchronization is expected to play a key role in emerging distributed and real-time applications such as the smart grid and Internet of Things (IoT) based applications. The Precision Time Protocol (PTP) is currently viewed as one of the main synchronization solutions over a packet-switched network, which supports microsecond synchronization accuracy. In this paper, we present a PTP simulation model for OMNeT++ INET, which allows to investigate the synchronization accuracy under different network configurations and conditions. To show some illustrative simulation results using the developed module, we investigate on the network load fluctuations and their impacts on the PTP performance by considering a network with class-based quality-of-service (QoS) support. The simulation results show that the network load significantly affects the network delay symmetry, and investigate a new technique called class probing to improve the PTP accuracy and mitigate the load fluctuation effects.

- by Martin Lévesque
- •
- Modeling and Simulation, Synchronization, Smart Grid, Simulation

Recent advances in micro-electromechanical (MEMS) technology have led to the development of small, low-cost, and low-power sensors. Wireless sensor networks (WSNs) are large-scale networks of such sensors, dedicated to observing and monitoring various aspects of the physical world. In such networks, data from each sensor is agglomerated using data fusion to form a single meaningful result, which makes time synchronization between sensors highly desirable. This paper surveys and evaluates existing clock synchronization protocols based on a palette of factors like precision, accuracy, cost, and complexity. The design considerations presented here can help developers either in choosing an existing synchronization protocol or in defining a new protocol that is best suited to the specific needs of a sensornetwork application. Finally, the survey provides a valuable framework by which designers can compare new and existing synchronization protocols.

- by Do Bui
- •
- Distributed Computing, Wireless Sensor Networks, Synchronization, Time Synchronization

Increasing broadband service penetration demands a transport network that delivers significantly lower cost-per-bit than traditional circuit-switched networks, and Ethernet provides the technology baseline for a cost-effective transport technology. For Ethernet to become a carrier-grade technology in wide area networks (WANs), operators and vendors have introduced several key technologies, including those necessary to address timing and synchronization requirements in WANs.

CiteSeerX - Document Details (Isaac Councill, Lee Giles): Since the Controller Area Network standard does not provide a clock synchronization service, many different solutions have been proposed to overcome this problem. Evaluation of... more

- by Julian Proenza
- •
- Clock synchronization
- by Aylin Kantarcı
- •
- Resource sharing, Distributed System, Clock synchronization

The pendulum clock was one of the most important metaphors for early modern philosophers. Christiaan Huygens (1629-1695) discovered his pendulum clock in 1656 based on the principle of isochronism discovered by Galileo (1564-1642). This paper aims at exploring the broad historical context of this invention, showing the role of some key figures such as Andreas Colvius (1594-1671), Elia Diodati (1576-1661), Hugo Grotius (1583-1645) and Constantijn Huygens, the father of Christiaan Huygens. Secondly, it suggests - based on this context - that it is hard to believe that Huygens did not know about Galileo's idea to construct a pendulum regulated clock. Finally, this article illustrates how the Dutch philosopher Spinoza (1632-1677) might have been inspired by Huygens' discovery of the synchronization of the pendulum clocks in his views on the agreement between bodies in the universe.

- by Filip A . Buyse
- •
- Philosophy, Early Modern History, Galileo Galilei, Benedict de Spinoza

Clock synchronization is a prerequisite for the realization of emerging applications in various domains such as industrial automation and the intelligent power grid. This paper surveys the standardized protocols and technologies for providing synchronization of devices connected by packet-switched networks. A review of synchronization impairments and the state-of-the-art mechanisms to improve the synchronization accuracy is then presented. Providing microsecond to sub-microsecond synchronization accuracy under the presence of asymmetric delays in a cost-effective manner is a challenging problem, and still an open issue in many application scenarios. Further, security is of significant importance for systems where timing is critical. The security threats and solutions to protect exchanged synchronization messages are also discussed.

- by Martin Lévesque
- •
- Synchronization, Smart Grid, Clock synchronization

The telecommunication networks of telecontrol systems in electric utilities have undergone an innovation process. This has removed many of their technical restrictions and made it possible to consider carrying out telecontrol tasks with general standard protocols instead of the specific ones that are used currently. These are defined in the standards 60870-5, 60870-6, and 61850 from the International Electrotechnical Commission, among others. This paper is about the implementation, using the services of general standard protocols, of the telecontrol application functions defined by the standard IEC 60870-5-104. The general protocols used to carry out telecontrol tasks are those used in the Internet: the telecommunication network-management protocol SNMPv3 (simple network management protocol version 3), the clock synchronization protocol network time protocol and Secure SHell. With this new implementation, we have achieved, among others, two important aims: 1) to improve performance and, above all, 2) to solve the serious security problems present in the telecontrol protocols currently being used. These problems were presented by IEEE in an article published in the website of the IEEE Standards Association. In this paper, the use of general standard protocols to perform the telecontrol of electrical networks is justified. The development of this paper-its achievements and conclusions and the tools used-is detailed.

A new digital implementation of a receiver for digital communications is presented. The receiver structure performs the integration of a maximum a posteriori probability (MAP) carrier and clock synchronisation with the maximum likelihood (ML) demodulation. It is shown that the key feature of the receiver structure is that the same hardware is able to perform both operations; thus the receiver implementation complexity is greatly reduced. This scheme can be adapted to different modulation techniques suitable for digital communications, such as QPSK, 0-QPSK and MSK. As examples, the application to QPSK and MSK signals is considered, owing to the interest of these modulation schemes for satellite communications.

- by Enrico Del Re
- •
- Computer Science, Modulation, Satellite Communication, Maximum Likelihood

Redes de Computadores -Congressos, Conferências, etc.//Comunicações em tempo real//redes locais//redes sem fios CDU 004.7 iii RTN 2004 3 rd Intl. Workshop on Real-Time Networks (formerly RTLIA) Satellite event to

- by Guillermo Rodriguez-navas
- •
- Clock synchronization
- by Nikolaus Kero
- •
- Digital Divide, Clock synchronization, High performance, Community Networks

Networked processing units are becoming widely used in the automotive embedded system domain aiming not only to reduce vehicle weight and cost but also to assist the driver to cope with critical situations. Because the fact that these embedded networked systems are strictly involved with human safety, there is a high demand on dependability requirements which can only be guaranteed if active redundancy is employed. Considering that the processing units are usually connected by a shared serial media, the underlying communication platform is the most important building block. It must provide low-level support for deterministic data transmission as well as a global time base to coordinate the actions of replicated units. Within this context, this paper presents the development of the fault-tolerant Daisy-Chain clock synchronization algorithm over the CAN protocol, resulting in an highly optimized communication architecture for safety-critical applications. Implementation issues and some obtained practical results are also discussed in the paper.

An experimental setup is proposed for comparing and analyzing clock synchronization algorithms in distributed system. Clock synchronization is required for transaction processing applications, process control applications etc. This experimental setup generates transmission delays and synchronization errors for processes and the clock synchronization algorithms try to synchronize the clocks in the system under the effect of these barriers. Two centralized clock synchronization algorithms are used for experiment-Cristian's and Berkeley clock synchronization algorithms.

- by Rahul Sehgal
- •
- Clock synchronization

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.

- by L. De Vito
- •
- OPERATING SYSTEM, Computer Network, Quality of Service, Clock synchronization

This is the first of a couple of papers in which the peculiar capabilities of the Hamiltonian approach to general relativity are exploited to get both new results concerning specific technical issues, and new insights about old foundational problems of the theory. The first paper includes: 1) a critical analysis of the various concepts of symmetry related to the Einstein-Hilbert Lagrangian viewpoint on the one hand, and to the Hamiltonian viewpoint, on the other. This analysis leads, in particular, to a re-interpretation of active diffeomorphisms as passive and metric-dependent dynamical symmetries of Einstein's equations, a re-interpretation which enables to disclose the (up to now unknown) connection of a subgroup of them to Hamiltonian gauge transformations on-shell;

- by Massimo Pauri and +1
- •
- Mathematical Physics, Quantum Physics, Quantum Gravity, General Relativity

The pendulum clock was one of the most important metaphors for early modern philosophers. Christiaan Huygens (1629-1695) discovered his pendulum clock in 1656 based on the principle of isochronism discovered by Galileo (1564-1642). This paper aims at exploring the broad historical context of this invention, showing the role of some key figures such as Andreas Colvius (1594-1671), Elia Diodati (1576-1661), Hugo Grotius (1583-1645) and Constantijn Huygens, the father of Christiaan Huygens. Secondly, it suggests - based on this context - that it is hard to believe that Huygens did not know about Galileo’s idea to construct a pendulum regulated clock. Finally, this article illustrates how the Dutch philosopher Spinoza (1632-1677) might have been inspired by Huygens’ discovery of the synchronization of the pendulum clocks in his views on the agreement between bodies in the universe.

- by Filip A . Buyse
- •
- Philosophy, Early Modern History, Galileo Galilei, Benedict de Spinoza

recently gained much attention as a potent method to leverage homeostatic circadian controls to ultimately improve clinical outcomes. Elucidation of the intrinsic properties of such complex systems and optimization of intervention strategies require not only an accurate identification of the signaling pathways that mediate host responses, but also a system-level description and evaluation.

Before 1905 Poincaré defined Lorentz's local time by means of a thought experiment in which observers synchronize their watches with light signals. In 1905 Einstein presented a similar thought experiment in his relativity paper. The similarity between Poincaré's and Einstein's thought experiment is striking. I suggest that Poincaré's thought experiment before 1905 may have indirectly assisted Einstein in formulating the theory that he had already discovered during the seven years of reflections between 1898 and 1905.

- by Galina Weinstein
- •
- Clock synchronization

This paper addresses an unbiased p-step predictive finite impulse response (FIR) filter of the local clock K-degree time interval error (TIE) polynomial model with applications to the Global Positioning System (GPS)-based clock synchronization. Generic coefficients are derived for a two-parameter family of the polynomial filter gains. A generalization is provided for the p-step linear (ramp) gain allowing for close to optimal predictive filtering of the TIE. Basic holdover algorithms are discussed along with their most critical properties. Efficiency of the proposed filter in holdover is demonstrated by simulation and in real applications to GPS-based (sawtooth and sawtooth-less) measurements of the TIE of a crystal clock.

All existing 4-coordinate systems centered on the world-line of an accelerated observer are only locally defined like it happens for Fermi coordinates both in special and general relativity. As a consequence, it is not known how non-inertial observers can build {\it equal-time surfaces} which a) correspond to a conventional observer-dependent definition of synchronization of distant clocks; b) are good Cauchy surfaces for Maxwell equations. Another type of coordinate singularities are those connected to the relativistic rotating coordinate systems (the rotating disk).We show that the use of Hamiltonian methods based on 3+1 splittings of space-time allows to define as many observer-dependent globally defined radar 4-coordinate systems as nice foliations of space-time with space-like hyper-surfaces admissible according to M$\o$ller (for instance only differentially rotating relativistic coordinate system are allowed). All these conventional notions of an {\it instantaneous 3-space} for an arbitrary observer can be empirically defined by introducing generalizations of Einstein 1over2{1\over 2}1over2 convention for clock synchronization in inertial frames. Each admissible 3+1 splitting corresponds to a non-rigid non-inertial frame centered on the observer. When there is a Lagrangian description of an isolated relativistic system, its reformulation as a parametrized Minkowski theory allows to show that all the admissible synchronization conventions are {\it gauge equivalent}, as it also happens in canonical metric and tetrad gravity, where, however, the chrono-geometrical structure of space-time is dynamically determined.

- by David Alba
- •
- Mathematical Physics, Quantum Physics, General Relativity, Clock synchronization

We study the coupling of N charged scalar particles plus the electro-magnetic field to ADM tetrad gravity and its canonical formulation in asymptotically Minkowskian space-times without super-translations. We make the canonical transformation to the York canonical basis, where there is a separation between the {\it inertial} (gauge) variables and the {\it tidal} ones inside the gravitational field and a special role of the Eulerian observers associated to the 3+1 splitting of space-time. The Dirac Hamiltonian is weakly equal to the weak ADM energy. The Hamilton equations in Schwinger time gauges are given explicitly. In the York basis they are naturally divided in four sets: a) the contracted Bianchi identities; b) the equations for the inertial gauge variables; c) the equations for the tidal ones; d) the equations for matter. Finally we give the restriction of the Hamilton equations and of the constraints to the family of {\it non-harmonic 3-orthogonal} gauges, in which the instantaneous Riemannian 3-spaces have a diagonal 3-metric. The non-fixed inertial gauge variable 3K{}^3K3K (the freedom in the clock synchronization convention) gives rise to a negative kinetic term in the weak ADM energy vanishing only in the gauges with 3K=0{}^3K = 03K=0: is it relevant for dark energy and back-reaction? In the second paper there will be the linearization of the theory to obtain Hamiltonian post-Minkowskian gravity with asymptotic Minkowski background, non-flat instantaneous 3-spaces and no post-Newtonian expansion. This will allow to explore the inertial effects induced by the York time 3K{}^3K3K in non-flat 3-spaces and to check how much dark matter can be explained as an inertial aspect of Einstein's general relativity.

- by David Alba
- •
- Dark Matter, Quantum Cosmology, High Energy Physics, Mathematical Sciences

The axiomatic bases of Special Relativity Theory (SRT) are thoroughly reexamined from an operational point of view, with particular emphasis on the status of Einstein synchronization in the light of the possibility of arbitrary synchronization procedures in inertial reference frames. Once correctly and explicitly phrased, the principles of SRT allow for a wide range of 'theories' that differ from the standard SRT only for the difference in the chosen synchronization procedures, but are wholly equivalent to SRT in predicting empirical facts. This results in the introduction, in the full background of SRT, of a suitable synchronization gauge. A complete hierarchy of synchronization gauges is introduced and elucidated, ranging from the useful Selleri synchronization gauge (which should lead, according to Selleri, to a multiplicity of theories alternative to SRT) to the more general Mansouri-Sexl synchronization gauge and, finally, to the even more general Anderson-Vetharaniam-Stedman's synchronization gauge. It is showed that all these gauges do not challenge the SRT, as claimed by Selleri, but simply lead to a number of formalisms which leave the geometrical structure of Minkowski spacetime unchanged. Several aspects of fundamental and applied interest related to the conventional aspect of the synchronization choice are discussed, encompassing the issue of the one-way velocity of light on inertial and rotating reference frames, the GPS's working, and the recasting of Maxwell equations in generic synchronizations. Finally, it is showed how the gauge freedom introduced in SRT can be exploited in order to give a clear explanation of the Sagnac effect for counter-propagating matter beams.

- by Guido Rizzi
- •
- Mathematics, Physics, General Relativity, Foundations of Physics

While Einstein clocks synchronization process is performed, one has a well defined region in which the clocks are synchronized and another one in which the clocks are not yet synchronized. The frontier between them evolves differently from the perspective of observers in relative motion. A discussion is conducted upon direct observation of the phenomenon and Minkowski diagrams.

- by Nilton Penha Silva
- •
- Clock synchronization

This paper investigates the design problem of adaptive controller and synchronizer for the Qi-Chen system (2005), when the system parameters are unknown. First, we build an adaptive controller to stabilize the Qi-Chen chaotic system to its unstable equilibrium at the origin. Then we build an adaptive synchronizer to achieve global chaos synchronization of the identical Qi-Chen chaotic systems with unknown parameters. The results derived for adaptive stabilization and adaptive synchronization for the Qi-Chen chaotic system are established using adaptive control theory and Lyapunov stability theory. Numerical simulations have been shown to demonstrate the effectiveness of the adaptive control and synchronization schemes derived in this paper for the Qi-Chen chaotic system.

This paper derives new results for the global chaos synchronization of identical Sprott L systems (1994), identical Sprott M systems (1994) and non-identical Sprott L and M systems. Active control method has been deployed to achieve the global chaos synchronization of the identical and different Sprott L and M systems. Our synchronization results have been established using Lyapunov stability theory. Numerical plots have been presented to show the effectiveness of the active synchronization results derived in this paper for the Sprott L and M systems.

The latest research works on the synchronization scheme for either continuous transmission mode or burst packet transmission mode for the wireless OFDM communications are overviewed in this paper. The typical algorithms dealing with the symbol timing synchronization, the carrier frequency synchronization as well as the sampling clock synchronization are briefly introduced and analyzed. Three improved methods for the fine symbol timing synchronization in frequency domain are also proposed, with several key issues on the synchronization for the OFDM systems discussed.

- by Bo Ai
- •
- Packet Switching, Synchronization, Algorithm, OFDM

Synchronisation is an important and critical issue in high-speed all optical time division multiplexed (OTDM) packet routing and transmission. In this paper we present a technique for separating the clock synchronization pulse from an incoming optical time division multiplexed data packet, based on all-optical switching devices with optical feedback. A 1X2 OTDM router composed of three Symmetric Mach-Zehnders (SMZs) is proposed. Simulation results show that synchronization between clock and data packet is achievable and the packet payload can be successfully switched to the correct destination port.

In the present paper, a new protocol for authentication and key distribution is proposed. The new protocol has the aim to achieve a comparable performance with the Kerberos protocol and overcome its drawbacks. For authentication of the exchanged messages during authentication and key distribution, the new protocol uses the Message Authentication Codes (MAC) to exchange the Diffie-Hellman components. On the

- by heba aslan
- •
- CMS, Clock synchronization, Diffie-Hellman-DSA, Key Distribution

Design of clock synchronization for networked nodes faces a fundamental trade-off between synchronization accuracy and univer-sality for heterogeneous platforms, because a high synchronization accuracy generally requires platform-dependent hardware-level network packet timestamping. This paper presents TouchSync, a new indoor clock synchronization approach for wearables that achieves millisecond accuracy while preserving universality in that it uses standard system calls only, such as reading system clock, sampling sensors, and sending/receiving network messages. The design of TouchSync is driven by a key finding from our extensive measurements that the skin electric potentials (SEPs) induced by powerline radiation are salient, periodic, and synchronous on a same wearer and even across different wearers. TouchSync integrates the SEP signal into the universal principle of Network Time Protocol and solves an integer ambiguity problem by fusing the ambiguous results in multiple synchronization rounds to conclude an accurate clock offset between two synchronizing wearables. With our shared code, TouchSync can be readily integrated into any wearable applications. Extensive evaluation based on our Arduino and TinyOS implementations shows that TouchSync's synchronization errors are below 3 and 7 milliseconds on the same wearer and between two wearers 10 kilometers apart, respectively.

- by Zhenyu Yan and +1
- •
- Ubiquitous Computing, Wearable Computing, The Internet of Things, Clock synchronization

In the Distributed Systems (DS) the nodes are communicating with each other using message passing. Many real-time applications such as banking systems, reservation systems that are implemented on distributed systems, it is important to execute each transaction/event in an ordered manner. Ordering of events is essential for proper allocation of available resources and mutual allocation. This can be implemented using clock synchronization. The paper presents a comparative study of clock synchronization algorithms in distributed systems. The paper also discusses time protocol such as Network Time Protocol and Simple Network Time Protocol.

AbstractWe study the problem of landmark selection for landmark-based routing in a network of fixed wireless com-munication nodes. We present a distributed landmark selection algorithm that does not rely on global clock synchronization,... more

- by Jie Gao
- •
- Computer Science, Distributed Algorithms, Routing, Wireless Sensor Networks

This paper presents PariSync, a distributed system for clock synchronization in DHT-based peer to peer networks. PariSync is formed by two modules: a topology module, that chooses for each node a small subset of neighbors with which to exchange timing information (piggybacking on the DHT link structure) and an extimation module, that assembles the information into an extimate of the node's offset and drift from a global virtual clock emerging from the consensus of all peers. PariSync works on extremely large peer-to-peer networks (millions of nodes) exhibiting good performance even in the presence of churn and malicious nodes. We provide a version of PariSync in pure Java and in JXTA.

- by Paolo Bertasi
- •
- Distributed System, Clock synchronization, Mobile Peer-to-Peer Network

The role of convention in various definitions of clock synchronization and simultaneity is investigated. We show that two principal methods of synchronization can be considered: system internal and system external synchronization. Synchronization by the Einstein procedure and by slow clock transport turn out to be equivalent if and only if the time dilatation factor is given by the Einstein result (1−v 2)1/2. An ether theory is constructed that maintains absolute simultaneity and is kinematically equivalent to special relativity.

- by reza mansouri
- •
- Mathematical Physics, Quantum Physics, Special Relativity, Clock synchronization

Continuous clock synchronization avoids unpredictable instantaneous corrections of clock values. This is usually achieved by spreading the clock correction over the synchronization interval. In the context of wireless real-time applications, a protocol achieving continuous clock synchronization must tolerate message losses and should have a low overhead in terms of the number of messages. This paper presents a clock synchronization protocol for continuous clock synchronization in wireless real-time applications. It extends the IEEE 802.1 1 standard for wireless local area networks. It provides continuous clock synchronization, improves the precision by exploiting the tightness of the communication medium, and tolerates message losses. Continuous clock synchronization is achieved with an advanced algorithm adjusting the clock rates. We present the design of the protocol, its mathematical analysis, and measurements of a driver level implementation of the protocol on Windows NT.

- by Edgar Nett
- •
- Information Technology, Synchronization, Distributed Systems, Protocols

If all clocks within a distributed system share the same notion of time, the application domain can gain several advantages. Among those is the possibility to implement real-time behavior, accurate time stamping, and event detection. However, with the wide spread application of clock synchronization another topic has to be taken into consideration: the fault tolerance. The well known clock synchronization protocol IEEE1588 (Precision Time Protocol, PTP), is based on a master/slave principle, which has one severe disadvantage. This disadvantage is the fact that the failure of a master automatically requires the re-election of a new master. The start of a master election based on timeout and thus takes a certain time span during which the clocks are not synchronized and thus running freely. Moreover the usage of a new master also requires new delay measurements, which prolong the time of uncertainty as well. This paper analyzes the results of such a master failure and proposes democratic master groups instead of hot-stand-by masters to overcome this problem by. It is shown by means of simulation that the proposed solution will not deteriorate the accuracy of the slave clocks in case of a master failure.

- by Nikolaus Kero
- •
- Distributed System, Event Detection, Computer Network, Distributed Processing

Wireless Sensor Networks (WSNs) can take advantage of versatility, completeness, and low prices of standard wireless protocols; Bluetooth as we will show later is a candidate suitable for WSNs. The fusion of data collected over a WSN is just an evident application of time synchronization. Bringing together these two issues, we find that synchronization using standard protocols poses an important drawback. In this paper, we present a simple method that allows clock synchronization in Bluetooth WSNs, down to few microseconds.

- by Jorge Falco
- •
- Computer Networks, Wireless Sensor Networks, Synchronization, Time Synchronization

This is the first of a couple of papers in which, by exploiting the capabilities of the Hamiltonian approach to general relativity, we get a number of technical achievements that are instrumental both for a disclosure of \emph{new} results concerning specific issues, and for new insights about \emph{old} foundational problems of the theory. The first paper includes: 1) a critical analysis of the various concepts of symmetry related to the Einstein-Hilbert Lagrangian viewpoint on the one hand, and to the Hamiltonian viewpoint, on the other. This analysis leads, in particular, to a re-interpretation of {\it active} diffeomorphisms as {\it passive and metric-dependent} dynamical symmetries of Einstein's equations, a re-interpretation which enables to disclose the (nearly unknown) connection of a subgroup of them to Hamiltonian gauge transformations {\it on-shell}; 2) a re-visitation of the canonical reduction of the ADM formulation of general relativity, with particular emphasis on the geometro-dynamical effects of the gauge-fixing procedure, which amounts to the definition of a \emph{global (non-inertial) space-time laboratory}. This analysis discloses the peculiar \emph{dynamical nature} that the traditional definition of distant simultaneity and clock-synchronization assume in general relativity, as well as the {\it gauge relatedness} of the "conventions" which generalize the classical Einstein's convention.

- by Massimo Pauri
- •
- Mathematical Physics, Quantum Physics, General Relativity, Clock synchronization
- by Dave Sayers
- •
- Languages and Linguistics, Sociolinguistics, Learning and Teaching, Academic Writing