Abstract: In this paper specific variants of delay attacks are examined. First, the Network Time Protocol is regarded. Second, delay attacks and implications on the time synchronization of the Precise Time Protocol are described. In particular, consequences for the offset calculation O prox are regarded. At the end of the paper possible countermeasurements are described.

Abstract: Delivery of accurate timing to subsea instruments is one of the essential functions of the NEPTUNE Canada ocean observatory. In the context of an ocean observing system, “timing” is understood to mean the ability to timestamp data using a clock which is traceable to Universal Time Coordinates (UTC) within some desired level of precision. Transmission or delivery of timing means transporting the necessary timing signals and data to subsea instruments or data collection processors. Timing signals are conventionally delivered in the form of a logic state transition on a dedicated communications line followed by a data string indicating the time at which the transition occurred. NEPTUNE Canada employs Ethernet communications channels to deliver timing. This avoids the need to provision additional communications channels and ensure that timing signals are available at all points within the network. The disadvantage of this approach is that timing signals must share the communications channels on which data is transmitted and may suffer delays or packet loss. Three timing protocols are employed: Network Time Protocol (NTP) described in IETF RFC 1305, Simple Network Time Protocol (SNTP) as described in RFC 2030 and IEEE 1588 Precision Time Protocol (PTP) per IEEE 1588. NTP/SNTP are generally accepted to be accurate to within a few milliseconds and are suitable for a wide variety of applications. PTP provides significantly better accuracy which is required for applications such as seismology and acoustic thermography. Master clocks located in the shore station acquire time from the Global Positioning System for transmission to subsea instruments. Alcatel-Lucent Submarine Networks and NEPTUNE Canada have successfully demonstrated PTP operation on a test bed which is representative of the NEPTUNE Canada network under simulated data traffic conditions, achieving a precision of ±10 microseconds or better. Ongoing development of IEEE 1588 will allow precision to within 100s of nanoseconds in future observatories. Science instruments which can take advantage of PTP timing delivery are currently under development.

Abstract: In this paper, a high-precision time synchronization technique is presented to solve the problems that the client clock is difficult to meet the accuracy of the time synchronization algorithm and the shortage of measuring network delay that produced when data packets of time synchronization are transmitted in the network. So a modified client clock is constructed to improve the accuracy of the clock. For this premise, the technique of Data Packet Selection is proposed, which is a method to determine whether to transfer by comparing the queue length of the router table with a specified value in the packet. By using this technique, the client clock precision can be raised to microsecond level, which can meet the time synchronization needs of NTP. Meanwhile, the optimized NTP time synchronization algorithm can also significantly reduce the errors that caused by the network delay. The emulation tests show this synchronization technique achieves the standard that the maximal offset is less than 10 milliseconds and the average of offset is less than 4 milliseconds as well as the average of standard deviation is less than 1 milliseconds.

Abstract: Distributed systems are notoriously difficult to implement and debug One important tool for understanding the behavior of distributed systems is tracing Unfortunately, effective tracing for modern distributed systems faces several challenges First, many interesting behaviors in distributed systems only occur rarely, or at full production scale Hence we need tracing mechanisms which impose minimal overhead, in order to allow always-on tracing of production instances Second, for high-speed systems, messages can be delivered in significantly less time than the error of traditional time synchronization techniques such as network time protocol (NTP), necessitating time adjustment techniques with much higher precision Third, distributed systems today may generate millions of events per second systemwide, resulting in traces consisting of billions of events Such large traces can overwhelm existing trace analysis tools These challenges make effective tracing difficult We present techniques that address these three challenges Our contributions include 1) a low-overhead tracing mechanism, which allows tracing of large systems without impacting their behavior or performance (014 μs/event), 2) a post hoc technique for producing highly accurate time synchronization across hosts (within 10 /ts, compared to between 100 μs to 2 ms for NTP), and 3) incremental data processing techniques which facilitate analyzing traces containing billions of trace points on desktop systems We have successfully applied these techniques to two distributed systems, a cooperative caching system and a distributed storage system, and from our experience, we believe our techniques are applicable to other distributed systems

Abstract: An Internet Protocol (IP)-based mobile TV system and a method for synchronizing the rendering of a streaming service are provided. In the IP-based mobile TV system, a plurality of mobile terminals receives a streaming service from network equipment, along with both a sequence of Network Time Protocol (NTP) time stamps corresponding to the streaming service and a synchronization clock. Each mobile terminal recovers an NTP reference clock for rendering the received streaming service according to both the synchronization clock and a synchronization time difference value, and then renders the received streaming service according to both the recovered NTP reference clock and the received NTP time stamps. Accordingly, the plurality of mobile terminals in the IP-based mobile TV system is able to render the received streaming service synchronously.

Abstract: The utility model relates to a time synchronous monitoring system which comprises an NTP server end and an NTP client end; a monitored clock which supplies NTP standard is set to be an NTP server mode, and the clock which does not supply the NTP standard collects time in real time as a server through a synchronous monitoring device; the NTP client end is arranged on a dispatching centre, and is connected with the NTP server end in an NTP communication mode through an Ethernet; and when the NTP client end asks the monitored clock time, each NTP server end transfers the time to the NTP client end in real time through NTP protocols, and the NTP client end is compared with the set reference time to obtain time deviation. The time synchronous monitoring system is used for electric power systems and monitors a plurality of clock devices in an electric network at the same time, judges synchronous cases of the clock of the electric network, compares the monitored clock time and the reference time, records a time deviation curve to be used for evaluating stability and precision of the clock device, and so find out whether the electric network clock is in a synchronous state.

Abstract: A time synchronization method includes the following steps. First, network communication equipment receives time information sent by at least two time servers respectively, in which the time information includes time synchronization status information of each of the time servers. Then, it is determined whether time synchronization status of each of the time servers is normal or not according to the time synchronization status information. Finally, the network communication equipment selects to employ the time information provided by the time servers with the normal time synchronization status from the at least two time servers. Network communication equipment and a network communication system are also provided correspondingly. The network communication equipment is capable of employing the time information provided by the time server with the normal time synchronization status according to the time synchronization status of each of the time servers, thereby improving precision and reliability of the time information obtained by the network communication equipment.

Abstract: The time synchronization modes in digital substation are pulse synchronization,code synchronization and network synchronization. The SNTP(Simple Network Transmission Protocol)-based time synchronization system of a digital substation is introduced,which is based on the time synchronization accuracy test system of SOE(Sequence of Events) resolution for the measuring and control device. Its station-level network adopts the 100 M Y-Y Ethernet and its bay-level has two RSG2100 exchangers. The time synchronization accuracy tests for different conditions,such as normal exchanger load,heavy exchanger load and heavy device CPU load show that,the main factors influencing the synchronization accuracy are:the master clock precision of SNTP time server,the communication load of station-level network,the CPU load of measuring and control device and the performance of network equipment. Test result shows that SNTP-based time synchronization system is a better solution for digital substation.

Abstract: In distributed applications, a group of multiple peer processes are required to cooperate with each other. Messages sent by peer processes have to be delivered in some order like causal order and total order. In this paper, we discuss a scalable group communication protocol for a group of multiple peers in peer-to-peer (P2P) overlay networks. Due to the message overhead O(n) for the number n of peer processes, the vector clock cannot be used to causally deliver messages. In this paper, we consider a group where every member peer process can use a physical clock which is synchronized with GPS time server in the network time protocol (NTP). The physical clock can be used to temporally order messages while the linear clock can be used to causally order messages. Even if each physical clock is synchronized with a time server, every physical clock does not show the same accurate time. The accuracy of the physical clock depends on distance, i.e. number of routers and traffic in a network. We discuss how the physical and linear types of clocks can be used to temporally and causally order messages in terms of delay time between peer processes and accuracy of each physical clock. In this paper, we discuss a group communication protocol to deliver messages by taking usage of physical clock and linear clock.

Abstract: There's no longer any excuse for having the wrong time. Computers, set-top boxes, and even some wristwatches can get their time from the U.S. Naval Observatory or some other authoritative source. But what about a device you build yourself? Many will come with a timing chip that you can use as a counter, but they won't tell you what time it is in the real world or self-adjust for daylight saving time. What you want is a microprocessor on a computer board that will query a network for the correct time and pass it on to the rest of your device. This month's project is just that, a clock on a singleboard computer that uses the Network Time Protocol (NTP) to give you millisecond accuracy for about US $115.

Abstract: Clock synchronization plays a crucial role in Wireless Sensor Networks (WSNs). Assuming that there is no clock skew between sensor nodes, the Maximum Likelihood Estimate (MLE) of clock offset was derived by [1] for clock synchronization protocols assuming exponential random delays and a two-way message exchange mechanism as in TPSN (Timing-sync Protocol for Sensor Networks [2]) or NTP (Network Time Protocol). The MLE is appropriate for the case that the random delays in WSNs are exponentially distributed. However, the performance of the MLE is deteriorated considerably in the case that the underlying distribution is contaminated by or mixed with other distributions. Hence, a robust estimator is needed. In this paper, clock offset estimators based on the robust M-estimation method are proposed and it is shown that the proposed estimators present excellent performance in the mean squared error (MSE) sense under the condition that the underlying distribution is mixed with other distribution.

Abstract: An Internet Protocol (IP)-based mobile TV system and a method for synchronizing the rendering of a streaming service are provided. In the IP-based mobile TV system, a plurality of mobile terminals (108, 110, 112) receives a streaming service from network equipment (104, 106), along with both a sequence of Network Time Protocol (NTP) time stamps corresponding to the streaming service and a synchronization clock. Each mobile terminal (108, 110, 112) recovers an NTP reference clock for rendering the received streaming service according to both the synchronization clock and a synchronization time difference value, and then renders the received streaming service according to both the recovered NTP reference clock and the received NTP time stamps. Accordingly, the plurality of mobile terminals (108, 110, 112) in the IP-based mobile TV system is able to render the received streaming service synchronously.

Abstract: NTP is a protocol designed to synchronize the clocks of computers over a network. This paper will implement the NTP on an embedded system to serve as a server of the NTP Pool Project. The developed embedded system is based on the embedded Linux operating system. The benefits of utilization of the embedded Linux system rely on its lower power consumption, high system stability, the small size of whole system including hardware and software, and no extra cost protected by the GPL license. All these characteristics will provide the embedded Linux system to be a suitable system for the implementation of the NTP that will need the services provided by many non-centralized servers. By setting multiple NTP servers in each network domain and utilizing NTP Pool Project guidelines, it will help to evenly distribute the throughput of each server and enhance the stability of the system. This paper will provide the detailed introduction on the protocol of NTP and the framework of the NTP Pool Project, the development of the NTP on the embedded system, and followed by the suggestions of the implementation of the NTP.

Abstract: The invention relates to a method for enhancing synchronization accuracy of network equipment of industrial Ethernet; at first, the method comprises, aiming at perturbed problem generated by uncertainness of communication protocol stack software in the process of execution, the following steps: 1, implementing phase alignment automatically upon the electrification of equipment; 2, simultaneously receiving synchronization messages and pulse-per-second signal of a time server on the network; 3, comparing local time with time of the time server; 4, judging the direction regulated by a local clock according to the received time message and the local time; 5, averagely assigning time deviation resulted from computation into synchronization intermittence; secondly, velocities of clock crystal oscillators of the equipment are deviated, and the method comprises the steps: A), setting maximal regulating amount of each synchronization intermittence upon the electrification; B), computing the regulating amount in this synchronization intermittence; C), computing regulating times in this synchronization intermittence; and D) averagely assigning the regulating amount to each regulation period.

Abstract: PROBLEM TO BE SOLVED: To provide a time synchronous system, time synchronous method, time server, and a positional information management server that identify a logical position in a network and share the receiving time based on obtained positional information. SOLUTION: In this time synchronous system, at least one time client and the positional information management server share time information with the time server. The time server includes a transmitting means for transmitting time information to the time client using a communication network I/F. The time client includes a setting means that obtains the positional information of the time server from the positional information management server, then communicates with the time server, obtains exact time about the time information from the transmitting means, and sets the obtained time. COPYRIGHT: (C)2009,JPO&INPIT

Abstract: A wireless base station capable of keeping an internal clock highly accurate even in a case where a malfunction occurs in an external time information notification server such as an NTP server. A wireless base station that performs wireless communication with a mobile terminal is connected to a plurality of time information notification servers. The wireless base station selects any of a plurality of pieces of time information notified from a plurality of time information notification servers, respectively, and corrects an internal clock based on the selected piece of time information. This can keep the internal clock of the wireless base station highly accurate.

Abstract: To develop the technology of time synchronize between NodeB and radio network controller(RNC) in TD-SCDMA,and change the status of global position system(GPS) as the only way to synchronize time,IEEE1588 V1 and IEEE1588 V2 are studied.Network time protocol(NTP) and simple network time protocol(SNTP) are also studied and compared with IEEE1588.IEEE1588 has higher time precision and accord with the TD-SCDMA system time precision requirement is proved.A solution base on the existing telecom network using IEEE1588 is proposed.

Abstract: Network Time Protocol (NTP) and Precision Time Protocol (PTP) have been used for time synchronization in many year. These protocols are not appropriated for IP over 802.15.4 like heterogeneous network because these are using Ethernet. To cope with this difficulty, we proposed IP over 802.15.4 time synchronization using 6LoWPAN (IPv6 over Low power Wireless Personal Area Networks) we could get accurate and precision time synchronization due to sending single packet. We implement IP over 802.15.4 FPGA board.

Abstract: Network time server and PCI timing card are two important devices of computer time synchronization. So it is necessary to research the features of them. In this paper, the two methods which synchronize accurate time to the computer based on the two devices were described. An effective PPS measurement method which shows synchronization accuracy and delay of each was made by using the computer parallel port. By comparing the results of two methods of synchronizing time, the different delay characteristics are analyzed in windows operating system environments. A more accurate synchronization can be achieved by reducing delay which can get a better the delay characteristics and delay compensation.

Abstract: The utility model discloses a network-type global satellite synchronizing clock which mainly comprises a GPS signal receiver and a GPS antenna connected with the GPS signal receiver and is characterized by also comprising a chip microprocessor, an NTP server and a pulse circuit, wherein the GPS signal receiver is respectively connected with the chip microprocessor and the pulse circuit, and the chip microprocessor is respectively connected with the pulse circuit and the NTP server The utility model has the advantages that the time precision is high, the output pulse per second precision can reach the microsecond level, the signal receiving is not limited by region condition, the manufacture cost is low and the reliability is high

Abstract: This paper proposes a compact time sharing system for home use applying the Simple Network Time Protocol. The compact SNTP server/client system for home appliances has been developed as an extension of an SNTP client application the authors previously proposed. The newly developed system can obtain the time from time detection sensors directly without upper layer NTP servers. For verification, the developed system operated on a real-time operating system, T-Kernel/Standard Extension, with a 32-bit RISC MPU, SH7727.

Abstract: PROBLEM TO BE SOLVED: To overcome the problem that it is necessary to manually and gradually switch time everyday since daily life of sailors is affected by changing the time at once when the time of the master clock is changed due to a change in a time-zone difference associated with a movement of a ship, and it is impractical to use such system in the ship since slave clock request the time to a NTP server at a regular interval and obtain the time and it takes a long time for the slave clock to follow the changed time of the master clock. SOLUTION: The master clock corrects a timing means to the correct time by using the correct time from a GPS satellite received by a GPS receiving means. If it is necessary to change the time due to the change in the time-zone difference associated with the movement of the ship, the time amount is input from an input means so as to change the time. A control is implemented so as to change the time in the timing means by the input time amount and collectively transmit the changed time to the slave clock. The slave clock maintains the time in its timing means, and displays the time in the timing means on a display means. COPYRIGHT: (C)2010,JPO&INPIT

Abstract: PROBLEM TO BE SOLVED: To prevent generation of a high load of time information acquisition request to an NTP (Network Time Protocol) server, even when power sources of many devices are switched to the on-state simultaneously at a power failure restoration time of a commercial power source, concerning a time information acquisition method and a device by NTP SOLUTION: A time interval for starting acquisition of time information to an NTP server 4-3 from the point of time when the power source of each device 1-1 is switched to the on-state is determined following a value of a random function generated in own device at every time when the power source is switched to the on-state, and acquisition of the time information is started to the NTP server 4-3 after elapse of the time interval from the point of time when the power source of the own device is switched to the on-state Otherwise, the time interval is determined by using low-order bit values of either or both of an IP address and an MAC address of the own device, and after elapse of the time interval, acquisition of the time information is started to the NTP server 4-3 COPYRIGHT: (C)2009,JPO&INPIT

Abstract: PROBLEM TO BE SOLVED: To eliminate a disadvantage that software to be developed in constructing a network system is increased and also an initial cost in construction and a management cost are increased since two kinds of servers (a processing server and a time server) are used in the above known network system in solving the problem that the transmission time of data of a client terminal has to be controlled depending on a network communication state when the client terminal periodically transmits data to the server via the network. SOLUTION: One server 1 has a function of controlling the transmission time of data of each client terminal 2 and a function of processing the data in this network system, thereby reducing the initial cost in construction and the management cost in a conventional network system. COPYRIGHT: (C)2009,JPO&INPIT

Abstract: The article introduces the present situation of time-synchronization networking in substations of power system, analyses the risk of GPS dependence, compares the time precision of different application systems in substations and the results of using NTP/DCLS/PTP networking. It suggests that the flat structure could be used as the main choice in timesynchronization networking and DCLS mode is used as the standby for emergency situation.

Abstract: PROBLEM TO BE SOLVED: To provide an reliable and authentic time to an external device such as electronic equipment. SOLUTION: The authenticity of TS time information included in a time stamp token obtained from a time certificate authority 3 is verified using electronic signature included in the time stamp token, and a time indicated by the TS time information authenticated as a result of verification is set as the time of a TS clock of a time providing device 6. Further, a time indicated by NTP(network time protocol) time information obtained from an NTP server 5 is set as a time of the NTP clock of the time providing device 6. Then, it is determined whether the time of the TS clock and the time of the NTP clock have a predetermined relation that both times are regarded to be coincident with each other. If they are regarded to be coincident with each other, the time of the NTP clock is output to a personal computer 10 of a service user. COPYRIGHT: (C)2009,JPO&INPIT

Abstract: Time synchronization of Substation Automation System (SAS) based on IEC61850 is studied in this paper. According to the request of time synchronization in SAS, the Network Time Protocol (NTP) is applied to SAS. Following the idea that the time offset is essentially caused by the frequency of clock itself so that it can be used for time synchronization with little or no additional cost, a new algorithm is presented, which adopts statistical technique to adjust the system clock frequency. The experimental results show that our algorithm has good performance to reduce the access frequency of time server and smooth time curves as well as meet the requirement of time synchronization in substation level.

Abstract: A basestation 20 (e.g. a femtocell basestation) of a telecommunications network is able to acquire timing information by sending a single time request message over a computer network 24, such as the internet, to a time server. The single request specifies a number of time response messages, said number being greater than one. Based on the received specified number of time response messages from the time server, the basestation is able to calibrate an internal oscillator 28.

Abstract: PROBLEM TO BE SOLVED: To solve, with the accuracy higher than that in the prior art, a problem resulting from low accuracy of a clock for measurement with an ordinary low-price personal computer in view of achieving higher accuracy of time stamp SOLUTION: A general purpose computer 4 receives first a notifying packet from a network time synchronous protocol (hereinafter, referred to as NTP) server 2 and presets the setting for asynchronization with a built-in clock The computer 4 also periodically executes the particular command for issuing an inquiry to the NTP server 2 and acquiring time information from a returning packet In addition, the computer 4 periodically monitors deviation of the time by the packets from the NTP server 2 and statistically evaluates results of the plurality of inquiries started from the first inquiry in order to calculate amount of correction of the time error and correct, based on the amount of correction, a value of time stamp when the communication packets transmitted to a measuring object client terminal 3 from a measuring object server 5 are captured COPYRIGHT: (C)2010,JPO&INPIT