Abstract: Internet of Things (IoT) is expected to change the everyday life of its users by enabling data exchanges among pervasive things through the Internet. Such a broad aim, however, puts prohibitive constraints on applications demanding time-synchronized operation for the chronological ordering of information or synchronous execution of some tasks, since in general the networks are formed by entities of widely varying resources. On one hand, the existing contemporary solutions for time synchronization, such as Network Time Protocol, do not easily tailor to resource-constrained devices, and on the other, the available solutions for constrained systems do not extend well to heterogeneous deployments. In this article, the time synchronization problems for IoT deployments for applications requiring a coherent notion of time are studied. Detailed derivations of the clock model and various clock relation models are provided. The clock synchronization methods are also presented for different models, and their expected performance are derived and illustrated. A survey of time synchronization protocols is provided to aid the IoT practitioners to select appropriate components for a deployment. The clock discipline algorithms are presented in a tutorial format, while the time synchronization methods are summarized as a survey. Therefore, this paper is a holistic overview of the available time synchronization methods for IoT deployments.

Abstract: Recently, new methods were discovered to secretly store information in network protocol caches by exploiting functionalities of ARP and SNMP. Such a covert storage cache is referred to as a "Dead Drop". In our present research, we demonstrate that hidden information can also be stored on systems with an active NTP service. We present one method based upon ephemeral associations and one method based upon the most recently used (MRU) list and measure their storage duration and capacity. Our approach improves over the previous approach with ARP as it allows to transport hidden information across the internet and thus outside of local area networks. The preliminary results for both Dead Drops indicate that more than 100 entries with secret data can persist for several hours. Finally, we discuss the detectability and countermeasures of the proposed methods as well as their limitations.

Abstract: Global navigation satellite systems (GNSS) provide pervasive accurate positioning and timing services for a large gamut of applications, from Time based One-Time Passwords (TOPT), to power grid and cellular systems. However, there can be security concerns for the applications due to the vulnerability of GNSS. It is important to observe that GNSS receivers are components of platforms, in principle having rich connectivity to different network infrastructures. Of particular interest is the access to a variety of timing sources, as those can be used to validate GNSS-provided location and time. Therefore, we consider off-the-shelf platforms and how to detect if the GNSS receiver is attacked or not, by cross-checking the GNSS time and time from other available sources. First, we survey different technologies to analyze their availability, accuracy and trustworthiness for time synchronization. Then, we propose a validation approach for absolute and relative time. Moreover, we design a framework and experimental setup for the evaluation of the results. Attacks can be detected based on WiFi supplied time when the adversary shifts the GNSS provided time, more than 23.942 μs; with Network Time Protocol (NTP) supplied time when the adversary-induced shift is more than 2.046 ms. Consequently, the proposal significantly limits the capability of an adversary to manipulate the victim GNSS receiver.

Abstract: Sensor networks require a high degree of synchronization in order to produce a stream of data useful for further purposes. Examples of time misalignment manifest as undesired artifacts when doing multi-camera bundle-adjustment or global positioning system (GPS) geo-localization for mapping. Network Time Protocol (NTP) variants of clock synchronization can provide accurate results, though present high variance conditioned by the environment and the channel load. We propose a new precise technique for software clock synchronization over a network of rigidly attached devices using gyroscope data. Gyroscope sensors, or IMU, provide a high-rate measurements that can be processed efficiently. We use optimization tools over the correlation signal of IMU data from a network of gyroscope sensors. Our method provides stable microseconds accuracy, regardless of the number of sensors and the conditions of the network. In this paper, we show the performance of the gyroscope software synchronization in a controlled environment, and we evaluate the performance in a sensor network of smartphones by our open-source Android App, Twist-n-Sync, that is publicly available.

Abstract: Information cross-validation can be a powerful tool to detect manipulated, dubious GNSS data. A promising approach is to leverage time obtained over networks a mobile device can connect to, and detect discrepancies between the GNSS-provided time and the network time. The challenge lies in having reliably both accurate and trustworthy network time as the basis for the GNSS attack detection. Here, we provide a concrete proposal that leverages, together with the network time servers, the nearly ubiquitous IEEE 802.11 (Wi-Fi) infrastructure. Our framework supports application-layer, secure and robust real time broadcasting by Wi-Fi Access Points (APs), based on hash chains and infrequent digital signatures verification to minimize computational and communication overhead, allowing mobile nodes to efficiently obtain authenticated and rich time information as they roam. We pair this method with Network Time Security (NTS), for enhanced resilience through multiple sources, available, ideally, simultaneously. We analyze the performance of our scheme in a dedicated setup, gauging the overhead for authenticated time data (Wi-Fi timestamped beacons and NTS). The results show that it is possible to provide security for the external to GNSS time sources, with minimal overhead for authentication and integrity, even when the GNSS-equipped nodes are mobile, and thus have short interactions with the WiFi infrastructure and possibly intermittent Internet connectivity, as well as limited resources.

Abstract: Internet of Things (IoT) devices that are wirelessly connected in mesh networks often need mutual clock time synchronization, to enable chronological ordering of sensor events, coordination of asynchronous processes across devices, or network-wide coordination of actuators. Accurate time synchronization is also critical for IoT device event logging and debugging. The widely-adopted Network Time Protocol (NTP) is less suitable for constrained mesh networks due to its high network load and sensitivity to asymmetric network delays. In this paper, Mesh Time-synchronization Protocol (MTP) is proposed for IP-based IoT wireless mesh networks and shown to outperform NTP. MTP exploits one resource-rich node on the mesh, the gateway or border router, to be the time reference or to synchronize with a (global/UTC) time reference. This reference time is efficiently disseminated throughout the mesh, using radio broadcasts. Our MTP implementation achieves a median accuracy of 0.48 ms, 1.01 ms, 1.50 ms, 2.06 ms on an event-driven embedded OS platform and 0.74 ms, 1.60 ms, 2.43 ms, 3.28 ms on a multi-threaded embedded platform respectively for mesh nodes 1, 2, 3 and 4 hops away from the gateway. Compared to NTP, the accuracy error variability over repeated measurements is an order of magnitude lower for MTP.

Abstract: Existing data acquisition literature for human behavior research provides wired solutions, mainly for controlled laboratory setups. In uncontrolled free-standing conversation settings, where participants are free to walk around, these solutions are unsuitable. While wireless solutions are employed in the broadcasting industry, they can be prohibitively expensive. In this work, we propose a modular and cost-effective wireless approach for synchronized multisensor data acquisition of social human behavior. Our core idea involves a cost-accuracy trade-off by using Network Time Protocol (NTP) as a source reference for all sensors. While commonly used as a reference in ubiquitous computing, NTP is widely considered to be insufficiently accurate as a reference for video applications, where Precision Time Protocol (PTP) or Global Positioning System (GPS) based references are preferred. We argue and show, however, that the latency introduced by using NTP as a source reference is adequate for human behavior research, and the subsequent cost and modularity benefits are a desirable trade-off for applications in this domain. We also describe one instantiation of the approach deployed in a real-world experiment to demonstrate the practicality of our setup in-the-wild.

Abstract: Existing data acquisition literature for human behavior research provides wired solutions, mainly for controlled laboratory setups. In uncontrolled free-standing conversation settings, where participants are free to walk around, these solutions are unsuitable. While wireless solutions are employed in the broadcasting industry, they can be prohibitively expensive. In this work, we propose a modular and cost-effective wireless approach for synchronized multisensor data acquisition of social human behavior. Our core idea involves a cost-accuracy trade-off by using Network Time Protocol (NTP) as a source reference for all sensors. While commonly used as a reference in ubiquitous computing, NTP is widely considered to be insufficiently accurate as a reference for video applications, where Precision Time Protocol (PTP) or Global Positioning System (GPS) based references are preferred. We argue and show, however, that the latency introduced by using NTP as a source reference is adequate for human behavior research, and the subsequent cost and modularity benefits are a desirable trade-off for applications in this domain. We also describe one instantiation of the approach deployed in a real-world experiment to demonstrate the practicality of our setup in-the-wild.

Abstract: Many devices are connected on the internet to give functionalities for interconnected services. In 2020', The number of devices connected to the internet will be reached 5.8 billion. Moreover, many connected service provider such as Google and Amazon, suggests edge computing and mesh networks to cope with this situation which the many devices completely connected on their networks. This paper introduces the current state of the introduction of the wireless mesh network and edge cloud in order to efficiently manage a large number of nodes in the exploding Internet of Things (IoT) network and introduces the existing Network Time Protocol (NTP). On the basis of this, we propose a relatively accurate time synchronization method, especially in heterogeneous mesh networks. Using this NTP, multiple time coordinators can be placed in a mesh network to find the delay error using the average delay time and the delay time of the time coordinator. Therefore, accurate time can be synchronized when implementing IoT, remote metering, and real-time media streaming using IoT mesh network.

Abstract: Network Time Protocol (NTP) is used by millions of hosts in Internet today to synchronize their clocks. Clock synchronization is necessary for many network applications to function correctly. Unsynchronized clock may lead to failure of various core Internet services including DNS and RPKI based interdomain routing and opens path for more sophisticated attacks. In this paper, we describe a new attack which can prevent a client configured in NTP's broadcast mode from synchronizing its clock with the server. We test the attack in real networks and show that it is effective in both authenticated and unauthenticated broadcast/multicast modes of NTP. We also perform experiments to measure the overall attack surface by scanning the entire IPv4 address space and show that NTP broadcast mode is being used in the wild by several low stratum (highly accurate) hosts. We also suggest few countermeasures to mitigate the proposed attack.

Abstract: This paper describes BigBen, a network telemetry processing system designed to enable accurate and timely reporting of Internet events (e.g., outages, attacks and configuration changes). BigBen is distinct from other Internet-wide event detection systems in its use of passive measurements of Network Time Protocol (NTP) traffic. We describe the architecture of BigBen, which includes (i) a distributed NTP traffic collection component, (ii) an Extract Transform Load (ETL) component, (iii) an event identification component, and (iv) a visualization and reporting component. We also describe a cloud-based implementation of BigBen developed to process large NTP data sets and provide daily event reporting. We demonstrate BigBen on a 15.5TB corpus of NTP data. We show that our implementation is efficient and could support hourly event reporting. We show that BigBen identifies a wide range of Internet events characterized by their location, scope and duration. We compare the events detected by BigBen vs. events detected by a large active probe-based detection system. We find only modest overlap and show how BigBen provides details on events that are not available from active measurements. Finally, we report on the perspective that BigBen provides on Internet events that were reported by third parties. In each case, BigBen confirms the event and provides details that were not available in prior reports, highlighting the utility of the passive, NTP-based approach.

Abstract: This paper presents HyNTP, a distributed hybrid algorithm that synchronizes the time and rate of a set of clocks connected over a network. Clock measurements of the nodes are given at aperiodic time instants and the controller at each node uses these measurements to achieve synchronization. Due to the continuous and impulsive nature of the clocks and the network, we introduce a hybrid system model to effectively capture the dynamics of the system and proposed hybrid algorithm. Moreover, the HyNTP algorithm allows each agent to estimate the skew of its internal clock in order to allow for synchronization to a common timer rate. We provide sufficient conditions guaranteeing synchronization of the timers, exponentially fast. Numerical results illustrate the synchronization property induced by the proposed algorithm as well as robustness to communication noise.

Abstract: The critical role that Network Time Protocol (NTP) plays in the Internet led to multiple efforts to secure it against time-shifting attacks. A recent proposal for enhancing the security of NTP with Chronos against on-path attackers seems the most promising one and is on a standardisation track of the IETF. In this work we demonstrate off-path attacks against Chronos enhanced NTP clients. The weak link is a central security feature of Chronos: The server pool generation mechanism using DNS. We show that the insecurity of DNS allows to subvert the security of Chronos making the time-shifting attacks against Chronos-NTP even easier than attacks against plain NTP.

Abstract: Because of its reliability demands, Industry has not previously trusted in commercial Ethernet for data communication, despite being the cheapest option and the de facto standard. Nevertheless, during the last years, some technological innovations have enhanced its safety and predictability so much, that Ethernet has turned into the industrial network. Critical sectors, such as Electric Power, with high-availability and strict timing requirement, have taken advantage of these developments, after having driven them.To allow some other crucial applications to get benefit from these innovations, the next step is providing system integrators with validated and compatible equipment. For this purpose, our paper presents a Smart PCIe card that delivers a common main clock throughout the industrial data network. Our design supports zero-delay recovery sub-standards (HSR and PRP), and autonomously manages Precise-Time-Protocol (PTP or IEEE 1588), for accurate synchronization over Ethernet. Besides, the board integrates a clock protocol gateway, so that legacy systems, not compatible with the PTP reference, can be synchronously attached. As an example, the presented use-case synchronizes a SCADA system by taking the time reference from the Windows Operating system that is synchronized using the native Network Time Protocol (NTP) slave. This clock is provided by the NTP master embedded in the PCIe card.

Abstract: Control system TimePictra and SyncView Plus synchronization equipment considered, which allow measurements in packet networks. In the latest versions of these control systems, it became possible to measure the stability parameters of outgoing and incoming synchronization signals on network synchronization equipment by means that are hardware implemented in this equipment and supported by the corresponding software in TimePictra and SyncView Plus control systems. TimePictra and SyncView Plus control systems make it possible to perform such internal measurements in packet networks. For example, PDV (Packet Delay Variation), packet MTIE (Maximum Time Interval Error), packet TDEV (Time Deviation), packet minTDEV measurements. That is, the measurement ideology that Microsemi proposed in its TimeAnalyzer 7500 measuring device has seamlessly switched to the synchronization network itself. Based on the considered control systems, the possibility of creating a monitoring system - synchronization signals stability (but today with certain limitations). The principles of creating a modern system for monitoring the synchronization network based on signal analysis using the NTP(Network Time Protocol) and PTP (Precision Time Protocol) protocols are proposed. A monitoring scheme for the quality of reference synchronization signals using the PTP and NTP protocols presented, which includes two local sources. One based on the GPS receiver (Global Positioning System). Second based on the local PTP1 server. PTP1 connected to the calibration circuit and the outgoing signal connected to the averaging scheme. It is also conditionally possible to replace the PTP server with NTP. The scheme considered universal for two protocols. A prototype of the interaction between the three NTP nodes and the central server described. This prototype makes it possible to demonstrate the principles of monitoring by majority rules. In case of accumulation of a sufficient amount of data, you can create a graph or fill in data arrays for further analysis.

Abstract: High precision, synchronized clocks are essential to a growing number of Internet applications. Standard protocols and their associated server infrastructure have been shown to typically enable client clocks to synchronize on the order of tens of milliseconds. We address one of the key challenges to high precision Internet timekeeping - the intrinsic contribution to clock error of path asymmetry between client and time server, a fundamental barrier to microsecond level accuracy. We first exploit results of a measurement study to quantify asymmetry and its effect on timing. We then describe three approaches to addressing the path asymmetry problem: LBBE, SBBE and K-SBBE, each based on timestamp exchange with multiple servers, with the goal of tightening bounds on asymmetry for each client. We explore their capabilities and limitations through simulation and argument. We show that substantial improvements are possible, and discuss whether, and how, the goal of microsecond accuracy might be attained.

Abstract: The new wave of computing allows users to explore their time in the Internet of Things (IoT) by connecting their smart devices over the network for data transfer without human interventions. While this swing increases the pace in IoT, time synchronization became a demanding feature on IoT devices for real-time applications. In this paper, we describe two synchronization protocols in IoT, its features and the advantages over the other. In addition, this work reveals the importance of time synchronization in the IoT platform and the effects of bad syncs in real-time applications. We start our research by analysing the widely using Simple Network Time Protocol (SNTP) and its performance in terms of offset and delay to examine the accuracy and reliability to define the synchronization.

Abstract: The paper considers the Network Time Protocol (NTP) algorithm. Mathematical model of an NTP-based unified time scale maintenance system is analyzed in depth. An implementation of an auxiliary model of I&C system based on "Network Calculus" techniques is proposed. Some practical aspects of time synchronization over the NTP Protocol in virtual environments are described.

Abstract: This document extends the specification of Network Time Protocol (NTP) version 4 in RFC 5905 with special modes called the NTP interleaved modes, that enable NTP servers to provide their clients and peers with more accurate transmit timestamps that are available only after transmitting NTP packets. More specifically, this document describes three modes: interleaved client/server, interleaved symmetric, and interleaved broadcast.

Abstract: Time-based wireless indoor localization recently stands as the state-of-the-art situation for the up-to-date real time application areas. Synchronizing time among the wireless nodes may still be the major challenging problem for time- based indoor localization on wireless networks. The main reason of this problem is the difficulty and complexity of using standard time synchronization protocols such as Network Time Protocol (NTP), and Coordinated Universal Time (UTC) on wireless networks. Besides, the limitations of the wireless networks restrict the consideration of which time synchronization protocols should be applied on which wireless communication technologies such as WiFi, LiFi, Bluetooth, UWB, Ultrasonic, ZigBee, etc, for wireless time synchronization. Generally, time synchronization schemes support better accuracy if and only if precise random delay model can be implemented for the estimation of random delay caused by the real environmental impacts. In this paper, a ZigBee-based hybrid wireless time synchronization approach, which is required as the first and vital step for time-based wireless indoor localization, is proposed. In order to provide precise synchronization accuracy of the proposed hybrid approach to be more precise, appropriate random delay model is implemented by applying the empirical approach on ZigBee- based test-bed. By using the empirical data obtained from anchor-to-anchor packet communications, random delay is estimated using Gaussian random delay model and then least square regression model is applied to improve synchronization accuracy. In accordance with the experimental evaluation results, it highlights that synchronization performance of the proposed approach is significantly improved.

Abstract: To prevent an image formation device, which obtains correct time information from a NTP server in order to correct held current time when the current time measured by a built-in RTC deviates from the correct time, from repeatedly accessing the NTP server when operation voltage of a RTC battery drops in a state in which the correct time is always obtained from the NTP server if the held current time deviatesSOLUTION: When the current time is corrected by obtaining time information from a NTP server, an access flag is set so that access to the NTP server is not be repeated until the access flag is cleared This allows suppressing access to the NTP server even when operation voltage of a RTC battery drops, reducing load of the server and a transmission pathSELECTED DRAWING: Figure 5

Abstract: Sensing applications with many sensors often rely on synchronized measurements in order to operate correctly. For wireless sensors connected via WLAN, the number of synchronization schemes is limited. Furthermore, the most popular method, Network Time Protocol (NTP), can often not guarantee the necessary accuracy, with errors ranging from ten to hundreds of milliseconds. Next to this method there are two major options: WizSync and Reference-Broadcast Infrastructure Synchronization (RBIS). However, these methods focus on a single access point solution. This translates into a synchronization area that is limited to the range of a single WLAN access point, which may not be sufficient in many large-scale applications. To tackle this problem, we have developed an extension to RBIS that can be used over a large range, spanning multiple access points, and with a synchronization error that is substantially smaller than that of NTP, i.e., less than 1 ms.

Abstract: The invention provides a time control encryption security enhancement method based on a random predicate model. The method comprises the steps that a time server generates system parameters and a timeserver public and private key pair according to a given security parameter k and a randomly selected generator, a system user generates a user public key according to the public parameters publishedby the time server, a sender operates a preset encryption algorithm to obtain a ciphertext according to a given to-be-sent message, the receiver public key, the time server public key and release time, and sends the ciphertext to the receiver, the time server generates a random number, generates a time trap door according to the random number and the time server private key, and broadcasts the time trap door to all system users, and the receiver operates the preset decryption algorithm to recover the message according to the received ciphertext, the receiver private key and the time trap doorcorresponding to the release time. According to the invention, one-time pad of the private key of the time server can be realized, the security of the private key of the time server is greatly enhanced, and the security and effectiveness of TRE are enhanced.

Abstract: In an information delivery system, the terminal transmits a first request requesting time information to a network server, the network server transmits a second request requesting time information to a time server connected to a network in response to the first request, the network server receives first time information as a response to the second request from the time server, and after a lapse of a predetermined time from reception of the first request, the network server transmits second time information measured based on the first time information to the terminal.

Abstract: Named Data Networking (NDN) architectural features, including multicast data delivery, stateful forwarding, and in-network data caching, have shown promise for applications such as video streaming and file sharing. However, collaborative applications, requiring a multi-producer participation introduce new NDN design challenges. In this paper, we highlight these challenges in the context of the Network Time Protocol (NTP) and one of its most widely-used deployments for NTP server discovery, the NTP pool project. We discuss the design requirements for the support of NTP and NTP pool and present general directions for the design of a time synchronization protocol over NDN, coined Named Data Networking Time Protocol (NDNTP).

Abstract: A method and system for enhanced time synchronization with lesser delay and jitter, from a gateway of a network or an external standard time source, over the internet, in a traditional network, including SDN, by NTP clients like newly added devices, spawned VMs and the like, by automatic deployment of the distributed NTP service through DHCP and DNS servers by spawning NTP demons (ntpd), according to the time synchronization requests received, thereby offloading the NTP functionality of the gateway and decreasing NTP traffic.

Abstract: The invention discloses a calendar clock synchronization system of an FC switching network system, which realizes high-precision synchronization of calendar time of the whole system and provides global consistent time service for each node in a network. A management mechanism of main and standby time servers is provided, and the time service reliability of the system is improved; high-precision clock synchronization is realized by fully utilizing a clock synchronization system of an FC-FS protocol; by means of the characteristics of low time delay, high determinacy, broadcast support and the like of the FC switching network, annual, monthly and daily broadcast transmission is realized; on the basis of a clock synchronization system of an FC-FS protocol, a management mechanism of main and standby time servers is provided to improve the system time service reliability.

Abstract: A time synchronization system includes at least one time server and a plurality of time clients connected to each other via a network. The time client comprises: a communication unit configured to obtain time information of the time server by transmitting/receiving messages to/from the time server; and a time count control unit configured to synchronize time information of an internal timepiece with time information of the time server. The time count control unit controls transmission of the messages by adjusting transmission intervals of the messages to irregular intervals.