Abstract: sensors network is a type of the ad-hoc network It is comprised of many sensors which are interlinked with each other for performing the same function collectively such as monitoring the weather conditions, temperature, different kind of vibrations and sound etc Any distributed system requires time synchronization In particular, time Synchronization is extremely important for Wireless sensor network applications eg for data fusion, TDMA schedules, synchronizes sleep periods, etc In this paper, we study different time synchronization protocols available for sensor networks, like Reference Broadcast Synchronization (RBS), Flooding Time Synchronization Protocol (FTSP) and Time Synchronization Protocol for Sensor networks (TPSN) Network Time Protocol (NTP) which is very famous in the computer network is also considered The simulations of these different protocols are performed on the sensor network with the help of a simulator The effects of these protocols on different parameters are studied and results obtained are compared Keywordssynchronization, clock synchronization, wireless sensor network

Abstract: Synchronizing clocks is an integral part of modern network and security architectures. However, the ability to synchronize clocks in modern networks is not well-understood. In this work, we use testbeds equipped with a high-accuracy GPS receiver to acquire ground truth, to study the accuracy of probe-based synchronization techniques to over 1861 public time servers. We find that existing synchronization protocols provide a median error of 2 - 5 ms, but suffer from a long-tail. We analyze sources of inaccuracy by decoupling and quantifying different network factors. We found that most inaccuracies stem from asymmetry of propagation delay and queueing delay. We discuss possible schemes to compensate these errors to improve synchronization accuracy.

Abstract: The invention discloses a time synchronization method and device and a distributed time synchronization system. The method comprises the following steps: receiving more than two time source information as time synchronization references; monitoring abnormity of the time source information; and selecting another time source information as the time synchronization standard when monitoring that one time source information is abnormal. The method, the device and the system have the following beneficial effects: the reliability of the system can be improved; the technical problems of low time synchronization reliability, difficulty in network maintenance and the like in the prior art can be solved; and the system can ensure the time source information of a time server to take each other as a reference, thus improving the reliability of the system.

Abstract: The invention discloses a method, system and device for keeping the clock synchronization of an NTP (Network Time Protocol) server. The method comprises the following steps of: synchronizing clocks from a telecommunication network time protocol (NTP-T) server by a first interactive network television network time protocol (NTP-I) server and a second NTP-I server; inquiring a first clock offset value with the second NTP-I server according to a preset time interval by the first NTP-I server; inquiring a second clock offset value with the second NTP-I server by the first NTP-I server when the first clock offset value exceeds a preset time difference threshold; and correcting a local clock by the first NTP-I server when the second clock offset value exceeds the preset time difference threshold. The invention can well keep the clock synchronization of the NTP server and avoids the clock disorder of the system.

Abstract: OWD is becoming increasingly important nowadays, as SLA agreements use it as a parameter to ensure QoS levels. However, its measurement is still a much debated topic due to the difficulty in the clock synchronization process. The paper approaches a new methodology to measure OWD, using NTP protocol with virtual clocks and bigger packets. This approach works over a measurement tool developed by the authors, called Netmetric, and is flexible enough to be applied in full-mesh networks, without lack in clock consistency during concurrent NTP synchronizations. The proposed method was validated using NTCUns simulator, tested over Vivo/Telefonica's 3G Network, and compared to OWAMP.

Abstract: Distributed Denial of Service (DDoS) attacks can be so powerful that they can easily deplete the computing resources or bandwidth of the potential targets. Based on the types of the targets, DDoS attacks can be addressed in two levels: application-level and network-level. Taking the network-based applications into consideration, a weak point is that they commonly open some known communication port(s), making themselves targets for denial of service (DoS) attacks. Considering adversaries that can eavesdrop and launch directed DoS attacks to the applications' open ports, solutions based on pseudorandom port-hopping have been suggested [1], [5], where applications defend the attacks to the communication ports by changing them periodically. As port-hopping needs the communicating parties to "hop" in a synchronized manner, these solutions suggest acknowledgment-based protocols between a client-server pair or assume the presence of synchronized clocks. Acknowledgments, if lost, can cause a port to be open for longer time and thus be vulnerable to DoS attacks, time servers for synchronizing clocks can become targets to DoS attack themselves. Following this line of research, in [2] we proposed a solution for port-hopping in the presence of clock-drifts, which are common in networking. The solution basically consists of two algorithms: H O P ER AA and B IG W HEEL. H O P ER AA enables each client to interact with the server independently of the other clients, B IG W HEEL enables a server to communicate with multiple clients in a port-hopping manner, without synchronizing with each client individually, which supports multi-party applications as well. Anti-DDoS solutions in the application-level, such as port-hopping, are ineffective when the DDoS attacks aim to congest the victim's network. Victims may need the help from network-based (i.e. in the router level) solutions to solve the problem. Among the network-based solutions against DDoS attacks, network-capability mechanism is a novel approach [6]. A capability is a ticket-like token, checkable by routers, that a server can issue for legitimate traffic. Still, malicious hosts may swamp a server with requests for capability establishment, essentially causing possible Denial-of-Capability (DoC). In [4] we proposed an algorithm to mitigate DoC attacks. With this algorithm, the legitimate hosts can get service with guaranteed probability. The algorithm divides the server's capacity for handling capability requests into quotas. Quotas are allocated based on a sink tree architecture. Randomization and Bloom filters are used as tools against threats (attacking scenarios). Issues on fault-tolerance and the deployment of the approach proposed were also addressed in [4]. The algorithm is not only suitable for solving DoC problem, but also suitable for general authentication-based solution against DDoS attacks, since legitimate hosts always need to get the secret for generating authentication tokens before sending data packets to the server. Mitigating DDoS attacks are challenging not only for the targets of the attacks, but also for the network, as large volume of illegitimate traffic share the same network resources as legitimate traffic and can furthermore causes congestion phenomena and performance degradation. Considering malicious traffic, we would like ideally to disallow it completely from consuming network resources. To achieve that, the malicious traffic should be controlled as close to the source(s) as possible. It is observed that there is a trade-off between the protection level of the network and the efficiency/overhead of the protecting method. By building on earlier work and improving on distribution of control aspects, in [3] we proposed a proactive method, called CluB, to mitigate DDoS attacks. The method balances the effectiveness-overhead trade-off by addressing the issue of granularity of control in the network. CluB can collaborate with different routing policies in the network, including contemporary data gram options. In [3] we estimated the effectiveness of the method and also studied a set of factors for tuning the granularity of control.

Abstract: According to the time synchronization requirements of IEC61850 at different levels of digital substation,three synchronization modes are compared:hard-wired,SNTP(Simple Network Time Protocol) and IEEE1588 PTP(Precision Time Protocol).The clock types of IEEE1588 and their relationships are introduced and the principle of IEEE1588 PTP synchronization is analyzed in detail.The feasibility of IEEE1588 PTP synchronization with current hardware supporting conditions of digital substation is described.Two schemes of IEEE1588 PTP application in IEC61850-based substation for future substation automation systems are proposed:one for single substation and the other for multiple substations.In the proposed schemes,the redundant configuration of grandmaster clock using Beidou navigation satellite system,GPS(Global Positioning System) and atomic clock is discussed.

Abstract: To synchronize clocks between spacecraft in proximity, the Proximity-1 Space Link Interleaved Time Synchronization (PITS) Protocol has been proposed. PITS is based on the NTP Interleaved On-Wire Protocol and is capable of being adapted and integrated into CCSDS Proximity-1 Space Link with minimal modifications. In this work, we discuss the correctness and liveness of PITS. Further, we analyze and evaluate the time synchronization latency performance with various channel error rates in different PITS operational modes.

Abstract: Distributed Denial of Service (DDoS) attacks can be so powerful that they can easily deplete the computing resources or bandwidth of the potential targets. Based on the types of the targets, DDoS attacks can be addressed in two levels: application-level and network-level. Taking the network-based applications into consideration, a weak point is that they commonly open some known communication port(s), making themselves targets for denial of service (DoS) attacks. Considering adversaries that can eavesdrop and launch directed DoS attacks to the applications' open ports, solutions based on pseudorandom port-hopping have been suggested [1], [5], where applications defend the attacks to the communication ports by changing them periodically. As port-hopping needs the communicating parties to "hop" in a synchronized manner, these solutions suggest acknowledgment-based protocols between a client-server pair or assume the presence of synchronized clocks. Acknowledgments, if lost, can cause a port to be open for longer time and thus be vulnerable to DoS attacks, time servers for synchronizing clocks can become targets to DoS attack themselves. Following this line of research, in [2] we proposed a solution for port-hopping in the presence of clock-drifts, which are common in networking. The solution basically consists of two algorithms: H O P ER AA and B IG W HEEL. H O P ER AA enables each client to interact with the server independently of the other clients, B IG W HEEL enables a server to communicate with multiple clients in a port-hopping manner, without synchronizing with each client individually, which supports multi-party applications as well. Anti-DDoS solutions in the application-level, such as port-hopping, are ineffective when the DDoS attacks aim to congest the victim's network. Victims may need the help from network-based (i.e. in the router level) solutions to solve the problem. Among the network-based solutions against DDoS attacks, network-capability mechanism is a novel approach [6]. A capability is a ticket-like token, checkable by routers, that a server can issue for legitimate traffic. Still, malicious hosts may swamp a server with requests for capability establishment, essentially causing possible Denial-of-Capability (DoC). In [4] we proposed an algorithm to mitigate DoC attacks. With this algorithm, the legitimate hosts can get service with guaranteed probability. The algorithm divides the server's capacity for handling capability requests into quotas. Quotas are allocated based on a sink tree architecture. Randomization and Bloom filters are used as tools against threats (attacking scenarios). Issues on fault-tolerance and the deployment of the approach proposed were also addressed in [4]. The algorithm is not only suitable for solving DoC problem, but also suitable for general authentication-based solution against DDoS attacks, since legitimate hosts always need to get the secret for generating authentication tokens before sending data packets to the server. Mitigating DDoS attacks are challenging not only for the targets of the attacks, but also for the network, as large volume of illegitimate traffic share the same network resources as legitimate traffic and can furthermore causes congestion phenomena and performance degradation. Considering malicious traffic, we would like ideally to disallow it completely from consuming network resources. To achieve that, the malicious traffic should be controlled as close to the source(s) as possible. It is observed that there is a trade-off between the protection level of the network and the efficiency/overhead of the protecting method. By building on earlier work and improving on distribution of control aspects, in [3] we proposed a proactive method, called CluB, to mitigate DDoS attacks. The method balances the effectiveness-overhead trade-off by addressing the issue of granularity of control in the network. CluB can collaborate with different routing policies in the network, including contemporary data gram options. In [3] we estimated the effectiveness of the method and also studied a set of factors for tuning the granularity of control.

Abstract: Many applications in industrial wireless sensor networks require time synchronization. Time synchronization is required for consistent distributed sensing and industrial control. In order to realize united time, the united time service system or the time server must be established. Based on industrial wireless sensor networks, information fusion automatically analyzes and monitors information under the certain criterion. In this paper, based on industrial wireless sensor network, time synchronization technology and fault-tolerance strategy of time synchronization are studied and the error analyses are given, the time correct value algorithm and the analyses to the synchronization result are proposed. Result shows that this method is feasible and can be used to wireless sensor networks.

Abstract: Recent developments in mobile telecommunication networks offer a possibility for synchronization of mobile equipment. The possibility is explored here. To this end, a network operator is synchronized to the Lithuanian national time and frequency standard over internet via NTP (Network Time Protocol). A mobile testing system (MTS) created is synchronized to the operator's network via a radio modem operating in one of the several different modes. The time scale of the MTS synchronized over the mobile telecommunication network is compared to that of the national standard to evaluate the synchronization accuracy and to find out that the most suitable operating mode for the modem is CSD (Circuit Switched Data), which is likely due to its dedicated and symmetrical nature.

Abstract: Saving energy, reducing costs, and increasing reliability are advantages of smart grid, but only if the safety of the system is guaranteed. To ensure correct operation, communications must be secure. A novel crypto graphic mechanism suitable for smart grid environments, namely the time-varying encryption system, is proposed in this paper. In the Ethernet network, the millisecond level time synchronization among client clocks and the server clock can be reached if they follow the Network Time Protocol (NTP). The time tags and some internal parameters for time synchronization are used for generating the encrypted cipher text at the transmission port. The same sets of time tags and internal parameters are used for recovering the information at the receiving port. Since the time tags and parameters are updated every second, the hacker approach of code-breaking with brute force will fail.

Abstract: The invention relates to a device and method for publishing wireless sensor network information based on a global navigation satellite system/network time protocol (GNSS/NTP), belonging to wireless sensor network technologies. In the method, time of each node in a wireless sensor network is respectively adjusted into international standard time consistent with a main control center by utilizing the NTP to ensure accuracy on the time of each sensor node, and an information publishing and feeding back device is developed on the basis of the integration and used for effective information publishing, remote control, information feedback of each terminal and the like of a laboratory and other occasions.

Abstract: In today's world of computer based control systems, there are so many applications which require precise timing. In order to maintain a precise time in those time needing systems, the time synchronization idea has been developed. Today there are many Commercial Products doing this job. In this paper we are trying to build a simple and Low Cost GPS Based Computer Network Time Synchronization Board, using NTP Protocol. This small leap can help effectively toward a giant leap of making an industrial Time Synchronization Product capable of synchronizing time of a real Distributed Control Systems(DCS).

Abstract: Nowadays, accurate and reliable time is an essential requirement in computer network based systems. To fulfill this necessity, time synchronization idea has been developed. Meanwhile in some cases, reliable time is so vital, therefore a redundant structure can be used. In this paper, a time synchronization system is investigated by designing and implementing a time synchronization board capable of synchronizing time of computer networks using NTP (Network Time Protocol). A redundant scheme is also embedded in this work to provide more reliability.

Abstract: PROBLEM TO BE SOLVED: To provide a correcting method for a clock correction period, correcting an internal clock correction period even in delay variation. SOLUTION: An NTP access for transmitting an NTP packet to an NTP server and receiving a response to the transmission of the NTP packet over the first frequency is executed, an access result with the highest reliability is extracted from execution results of the NTP access step, and the extracted result is determined as a transmission line delay to the NTP server. The above steps are repeatedly executed in an NTP access period which is shorter than the internal clock correction period. When it is determined that a difference between the determined transmission line delay and a transmission line delay for a preceding correction period, exceeds or equals a predetermined threshold over second continuous frequencies, a deviation of the correction periods is corrected. COPYRIGHT: (C)2011,JPO&INPIT

Abstract: A more simple and robust time synchronization of network subscribers compared to solutions known in the state of the art is provided by a device for time synchronization of network subscribers of a network based on satellites, having at least one satellite antenna connected to a receiving unit receiving a satellite signal containing time information. An electronic system that obtains the time from the satellite signal is connected to a time server with a network connection for the synchronization of the network subscribers using a network protocol. The complexity of the device is reduced and the common coaxial infrastructure between the receiving unit and the time server is removed for the satellite signal and replaced by a robust infrastructure.

Abstract: I have used the Kalman Filter algorithm to improve the link between the Internet Time Servers operated by the National Institute of Standards and Technology (NIST) and the primary atomic clock ensemble in Boulder, which realizes UTC(NIST) and which is used as the reference for the time servers. The Kalman algorithm is better able to separate the contributions of multiple noise sources such as the fluctuations in the asymmetry of the channel delay and the statistical fluctuations in the clock used as the internal reference for the time server. This improved separation has made it possible to compensate to some extent for the lower-quality telephone circuits that are often used as the links for synchronizing the time servers to the atomic clock ensemble.

Abstract: The present invention discloses a method for performing clock synchronization among devices. The method includes the following steps: step A, performing a coarse synchronization between the clock of a home end and an opposite end by using the Network Time Protocol; step B, initiating, by the home end, a two-way network delay measurement, and obtaining a TxTimeStampb representing the time when the home end transmits a message, an RxTimeb representing the time when the home end receives a response message, and a Single-Delay representing a one-way frame delay; step C, executing the step B for multiple times, and calculating an average value of the TxTimeStampb, an average value of the RxTimeb, and a one-way frame average delay; step D, calculating a time correction value; step E, correcting a local current time on the basis of the time correction value. The present invention also discloses an apparatus for performing clock synchronization among devices. This invention calculates the delay among devices, by using the Two-way Delay Measurement (TWO-DM) function, for multiple times, acquires the one-way frame average delay among devices, and corrects a local current time through the local current time of the device and the one-way frame average delay, so as to realize a clock synchronization among devices with high accuracy up to nanosecond scale.

Abstract: PROBLEM TO BE SOLVED: To obtain a wireless base station apparatus increasing the success rate of reference clock correction SOLUTION: The device includes: a memory part 2 for storing time data obtained from a time server and determination results of whether the time data can be used for reference clock correction or not; a time data obtaining part 1 for requiring the time server to provide the time data, and storing in the memory part 2 the time data obtained as response of the requiring; a time data determination part 3 for determining whether the time data stored in the memory part 2 can be used for reference clock correction or not, and storing in the memory part 2 the determination results associated with the time data; and a correction control part 4 for reading latest time data obtained from the same time server and time data obtained in the past, out of the usable time data stored in the memory part 2, and correcting the reference clock based on the read data COPYRIGHT: (C)2011,JPO&INPIT

Abstract: An algorithm to realize system time alignment based on TNP protocol is put forwarded in the paper.The algorithm used in large electronic information system,A NTP server group is constructed by accurate external time source and several stable hosts in the system and accurate time alignment can be performed for other network hosts by the NTP server group.The accuracy can be of millisecond.

Abstract: PROBLEM TO BE SOLVED: To start a main system with an acquired accurate time as an initial time after a sub-system acquires the accurate time synchronized with an NTP server even if the NTP server is not connected to a management LAN to which the subsystem is connected, in an information processor having the main system for providing prescribed functions as an information processor and the sub-system for managing the main systemSOLUTION: The boot loader of the main system of the information processor is provided with a function of accessing the NTP server, and the sub-system acquires the accurate time by using the function, and then the acquired accurate time is used as the initial time to start the main system

Abstract: Network Time Protocol(NTP) is a time synchronization protocol based on UDPThis paper introduces the basic principles of NTP,and analyzes the time synchronization error brieflyDifferent implementation methods of NTP are comparedThe configuration and behavior pattern of NTPD service on the UNIX platform are analyzed thoroughlyBased on this,the classical configuration of NTP service on different platforms of Windows,UNIX,and network device is providedConsidering the application requirements of power enterprises and the economic and flexibility demands,a hierarchical architecture of NTP service is proposedIt is implemented in the information network of Anhui Electric Power Corporation,and gets good application effects

Abstract: The invention provides a method, device and system for reporting time offsets (TOFF) of a network time protocol (NTP) network. In the method, an NTP server samples the TOFFs of a NTP client-side at intervals of a first set time, acquires the maximum TOFF in sampled data obtained in each sampling, and saves the maximum TOFFs as first TOFFs; when a performance management server (PMS) collects the TOFFs from the NTP server, the NTP server acquires TOFFs at intervals of a second set time from the first TOFFs so as to obtain a plurality of second TOFFs, acquires the maximum TOFF and the minimum TOFF in each second TOFF and saves the maximum TOFFs and the minimum TOFFs as third TOFFs; and the NTP server sends the third TOFFs to the PMS, wherein the first set time is less than the second set time.

Abstract: A first and a second base station, and respective methods therein are provided for enabling communication between the first base station and the second base station, wherein one of the base stations enables the other base station to obtain synchronization information. One of the base stations has information of a time server it is using for obtaining synchronization information. When one of the base stations detects the presence of the other, this time server information is sent to the base station not having the time server information, thereby enabling this base station to obtain synchronization information from the same time server as its counterpart.

Abstract: A wireless sensor networks (WSNs) is typically made up of numerous sensors which have different clock accuracies. Time synchronization is crucial to maintain data consistency, coordination, and perform other fundamental operations: power management, security, and data fusion and scheduling. In order to realize united time, the united time service system or the time server must be established. In this paper, based on industrial wireless sensor network, Sliding Window Algorithm and fault-tolerance strategy of time synchronization are studied and the error analyses are given. The proposed algorithm has lower average synchronization error compared to the existing algorithms.

Abstract: In the meteorological field,establishing an accurate,steady and reliable unified meteorological system clock source is of very important practical significance and application value for dealing with various kinds of meteorological business.First we analyze the principle,realization way and operation mode of NTP-based clock synchronization system,then introduce the NTP implementation in meteorological networks,finally describe the establishment of NTP server and client.

Abstract: This paper deals with the problem of generation of 1-pps timing signal at the output of computer interface controlled by Network Time Protocol. The methods of synchronization of internal computer clock and transmission of the timing signal to the serial interface are described. The results of the measurement of obtained signals are presented.