Search Results (15)

Clock synchronization is one of the popular research topics in Distributed Measurement and Control Systems (DMCSs). In most industrial fields, such as Smart Grid and Flight Test, the highest requirement for synchronization accuracy is 1 μs. IEEE 1588 Precision Time Protocol-2008 (PTPv2) can theoretically achieve sub-microsecond accuracy, but it relies on the assumption that the forward and backward delays of PTP packets are symmetrical. In practice, PTP packets will experience random queue delays in switches, making the above assumption challenging to satisfy and causing poor synchronization accuracy. Although using switches supporting the Transparent Clock (TC) can improve synchronization accuracy, these dedicated switches are generally expensive. This paper designs a PTP clock servo for compensating Queue-Induced Delay Asymmetry (QIDA), which can be implemented based on ordinary switches. Its main algorithm comprises a minimum window filter with drift compensation and a fuzzy proportional–integral (PI) controller. We construct a low-cost hardware platform (the cost of each node is within USD 10) to test the performance of the clock servo. In a 100 Mbps network with background (BG) traffic of less than 70 Mbps, the maximum absolute time error (max |TE|) does not exceed 0.35 μs, and the convergence time is about half a minute. The accuracy is improved hundreds of times compared with other existing clock servos. Full article

The 3GPP release 16 integrates TSN functionality into 5G and standardizes various options for TSN time synchronization over 5G such as transparent mode and bridge mode. The time domains for the TSN network and the 5G network are kept separate with an option to synchronize either of the networks to the other. The TSN time synchronization over 5G is possible either by using the IEEE 1588 generalized Precision Time Protocol (gPTP) based on UDP/IP multicast or via IEEE 802.1AS based on Ethernet PDUs. The INET and Simu5G simulation frameworks, which are both based on the OMNeT++ discrete event simulator, are widely used for simulating TSN and 5G networks. The INET framework comprises the 802.1AS based time synchronization mechanism, and Simu5G provides the 5G user plane carrying IP PDUs. We modified the 802.1AS-based synchronization model of INET so that it works over UDP/IP. With that, it is possible to synchronize TSN slaves (connected to 5G UEs), across a 5G network, with a TSN master clock, present within a TSN network, that is connected to the 5G core network. Our simulation results show that 500 microseconds of synchronization accuracy can be achieved with the corrected asymmetric propagation delay of uplink and downlink between the gNodeB (gNB) and the User Equipment (UE). Furthermore, the synchronization accuracy can be improved if the delay difference between uplink and downlink is known. Full article

IEEE 1588, also known as the Precision Time Protocol (PTP), is a standard protocol for clock synchronization in distributed systems. While it is not architecture-specific, implementing IEEE 1588 on Reduced Instruction Set Computer-V (RISC-V) low-power embedded devices demands considering the system requirements and available resources. This paper explores various approaches and techniques to achieve accurate time synchronization in such instruments. The analysis covers software and hardware implementations, discussing each method’s challenges, benefits, and trade-offs. By examining the state-of-the-art in this field, this paper provides valuable insights and guidance for researchers and engineers working on time-critical applications in RISC-V-based embedded systems, aiding in selecting the most-suitable stack for their designs. Full article

With the vigorous development of industrial automation and the Internet of things, the transmission of data is more dependent on immediacy, so network devices have higher and higher requirements for time synchronization accuracy. The clock source of common network devices is provided by the transistor oscillator in the server, but the oscillator will change with factors such as aging and temperature, and it cannot be guaranteed that the oscillator in the server will work at the same frequency. Time synchronization can be achieved by technologies such as IRIG-B, NTP, or IEEE 1588 (PTP), but the hardware cost of building IRIG-B is high, and NTP has the lowest cost, but it can only provide time accuracy from milliseconds to microseconds. PTP can provide sub-microsecond or even nanosecond time precision. It is a system of time synchronization mechanisms through Ethernet transmission. In this article, we first propose a time synchronization system using the development board and PDP protocol. On the Xilinx Zynq-7000 SOC platform of Petalinux, we implement the hardware solution of Linux PTP. The hardware time stamp is 20 ns. To improve the accuracy, the congenital frequency error between the oscillators must be considered. Therefore, a PTP auxiliary time stamp with dynamic frequency compensation is proposed and designed into a chip. Experimental results show that at 45 nm (TN40G) it can operate at 370 MHz and achieve 2.7 ns resolution, which can be applied to more demands. Full article

The performance of time-critical systems depends heavily on time synchronization accuracy. Therefore, it is crucial to have a synchronization method that can achieve high time synchronization accuracy. In this paper, we propose a new underlying transmission architecture and new synchronization messages. On the basis of these, aiming at the time error problem of the slave clock, we propose an enhanced time synchronization method based on new synchronization messages. Furthermore, we evaluate the performance of the enhanced time synchronization method on the OMNeT++ simulator. In addition, we compare the impact of different crystal oscillator accuracies and different crystal oscillator frequencies on time synchronization accuracy, respectively. Simulation results show that the time offset is at most ±1 clock period using the enhanced time synchronization method. We realize the purpose of timing the master clock and the slave clock by counting the period of the clock signal. Therefore, we needed to round down the time count to an integer. This is the reason why −1 and 1 appear at the same time. When the crystal oscillator frequency used is 80 MHz, the system can achieve a time synchronization accuracy of ±12.5 ns; that is, a nanosecond-level time synchronization accuracy can be achieved. With the reduction of the crystal oscillator accuracy of the slave clock, the synchronization accuracy of ±1 clock period can still be achieved. With the increase in the crystal oscillator frequency, the time synchronization accuracy that can be achieved also improves. The method proposed in this paper provides a new way of thinking and has certain guiding significance for improving the time synchronization accuracy of time-critical systems. Full article

The Precision Time Protocol (PTP) as described in IEEE 1588–2019 provides a sophisticated mechanism to achieve microsecond or even sub-microsecond synchronization of computer clocks in a well-designed and managed network, therefore meeting the needs of even the most time-sensitive industrial and financial applications. However, PTP is prone to many security threats that impact on a correct clock synchronization, leading to potentially devastating consequences. Here, the most vicious attacks are internal attacks, where a threat actor has full access to the infrastructure including any cryptographic keys used. This paper builds on existing research on the impact of internal attack strategies on PTP networks. It shows limitations of existing security approaches to tackle internal attacks and proposes a new security approach using a trusted supervisor node (TSN), in line with prong D as specified in IEEE 1588–2019. A TSN collects and analyzes delay and offset outputs of monitored slaves, as well as timestamps embedded in PTP synchronization messages, allowing it to detect abnormal patterns that point to an attack. The paper distinguishes between two types of TSN with different capabilities and proposes two different detection algorithms. Experiments show the ability of the proposed method to detect all internal PTP attacks, while outlining its limitations. Full article

With the advent of a new Precision Time Protocol specification, new opportunities abound for clock synchronization possibilities within power grid control systems. The third iteration of the Institute of Electrical and Electronics Engineers Standard 1588 specification provides several new features specifically aimed at complex, wide-area deployments in which situational awareness and control require precise time agreement. This paper describes the challenges faced by existing technology, introduces the new time distribution specification, and provides examples to explain how it represents a game-changing innovation. Full article

The use of wireless communication systems in industrial environments is gaining international importance. The requirements, which are placed thereby on the communication systems, are manifold depending on the specific use. In the field of industrial manufacturing, however, many applications are characterized by high reliability requirements and hard real-time demands. The latter requires a time-deterministic handling of processed transmissions and therefore requires the use of Time-Sensitive Networking (TSN) solutions. In this paper, we briefly describe which functionalities characterize a wireless TSN system and which approaches have already been pursued in the literature and standardization. Subsequently, we present a concept for a toolbox that allows one to combine the required functionalities into a working solution, which can be used as a guideline for software-based implementation. Additionally, since reliability of transmissions is one of the key challenges, especially in wireless communication, to achieve a performance comparable to wired systems, we provide some further design considerations to improve. Full article

Time-synchronization technology can provide a common notion of time among the participating nodes on a network. This is essential not only for protocol operation for time-critical services but also for the time stamp for information included in the message. Precise time information can be very crucial for such things as autonomous driving because there are various sensor measurements from multiple cameras, and radio detection and ranging (radar) and light detection and ranging (LiDAR) are used for perceiving the current situation via sensor fusion. A well-known synchronization method, IEEE 1588, denoted as the precision time protocol (PTP), can be used for various applications. For in-vehicle networks of autonomous cars, we have to consider that the network may be comprised of subnetworks based on different protocols such as controller area network (CAN) and Ethernet. However, implementing PTPs on such heterogeneous vehicle networks causes several problems. First, the PTP procedure must be modified to be implement on a CAN network. Second, to calculate the delay and offset for PTP, the processing delay that occurs during message conversion must be considered. In this paper, we propose a synchronization method for CAN–Ethernet networks to solve these problems. The performance of the proposed synchronization method is evaluated by experiments on a real CAN–Ethernet network. Full article

This paper proposes a distributed nodes-based clock synchronization method to sustain sub-microsecond precision synchronization of slave clocks upon master clock failure in IEEE 1588 PTP (precision time protocol) system. The sustaining is achieved by synchronizing the slave clocks to the estimated reference clock which is obtained from the analysis of distributed slave clocks. The proposed method consists of two clock correction functions (i.e., a self-correction and a collaborative correction, respectively). Upon master failure, the self-correction estimates a clock correction value based on the clock model which is constructed during normal PTP operation. The collaborative correction is performed in the preselected management node. The management node estimates a reference clock by collecting and analyzing clock information gathered from the other slave clocks. The performance of the proposed method is simulated by computer to show its usefulness. It is confirmed that the fifty (50) clock model-based collaborative correction maintains 10⁻⁶ second PTP accuracy for 10 min prolonged period after the master failure when tested with clock offset variations less than 50 ppm. Full article

The IEEE 1588 precision time protocol (PTP) is used by many time-sensitive applications and systems, as it achieves sub-microsecond time synchronization between computer clocks. However, a PTP network is vulnerable to cyber-attacks that can reduce the protocol accuracy to unacceptable levels for some or all clocks in a network with potentially devastating consequences. Of particular concern are advanced persistent threats (APT), where an actor infiltrates a network and operates stealthily and over extended periods of time before being discovered. This paper investigates the impact of the most important APT strategies on a PTP network, i.e., the delay attack, packet modification or transparent clock attack, and time reference attack, using a fully programable and customizable man in the middle device, thereby considering the two most popular PTP slave daemons PTPd and PTP4l. In doing so, it determines suitable attack patterns and parameters to compromise the time synchronization covertly. Full article

In this paper, an improved time-synchronization algorithm is proposed. The improvement of time synchronizing performance was achieved by introducing a stochastic model-based direct compensation of the disturbance effects appearing in the IEEE 1588 Precision Time Protocol (PTP)-based time synchronization system. A dynamic model of PTP clock system was obtained by reflecting the three major sources of disturbances, i.e., clock frequency drift, clock rate offset, and network noise. With the application of the dynamic model of the PTP clock system, the effects of the disturbances can be effectively eliminated in the PTP time synchronization control loop. Computer simulations are performed to verify the performance of the proposed time synchronization algorithm by applying the various types of disturbances, including network noise and clock drift. The simulation results are compared with those of other representative time synchronization algorithms, i.e., IEEE 1588 PTP algorithm and Kalman-filter-based algorithm. It is shown that the proposed algorithm improves time synchronizing performance up to 84% with respect to that of the Kalman-filter-based synchronization algorithm when simulated with colored noise type disturbances. The proposed time synchronization algorithm is expected to contribute for the realization of future Ethernet-based industry-plant monitoring and control including IEC 61850-based digital substation. Full article

In this paper, the effect of time synchronization error on protection algorithms are studied for the usage of the LAN-based collaborative protection. In order to derive the effect of time synchronization, this paper proposes a substation model which is constructed with IEEE 1588 Precision Time Protocol (PTP) supported intelligent electronic devices. The proposed model is used as an example of a target platform to study the effect of time synchronization error with two typical substation protection algorithms, i.e., current differential-based substation protection and distance protection algorithms. From the analyzed and the simulated results, it was well observed that time synchronization error is a significant error-causing factor for both protection algorithms, resulting in erroneous detection of faults and erroneous estimation of fault distances, respectively. The results of research performed in this paper are expected to provide a good guide for constructing the future LAN-based digital power substation with precise time synchronization. Full article

Accurate and precise clock synchronization is one of the fundamental requirements for various applications, such as telecommunication systems, measurement and control systems, and smart grid systems. Precision time protocol (PTP) was designed and specified in IEEE 1588 to meet that requirement. PTP provides a mechanism for synchronizing the clocks in a PTP system to a high degree of accuracy and precision based on exchange synchronization messages through a master–slave hierarchy. The best master clock (BMC) algorithm is currently used to establish the master–slave hierarchy for PTP. However, the BMC algorithm does not provide a fast recovery mechanism in case of master failures. The accuracy and precision of the PTP clocks could be deteriorated by the occurrence of failure in the network (link or node failure). These fault occurrences will affect network performance and reliability, and cause clock time drifting of the PTP nodes. In this paper, we present a novel approach, called timing fault recovery (TFR), to significantly reduce clock time drifting in PTP systems. TFR detects the fault occurrence in the network and recovers it by using a handshake mechanism with a short duration. Therefore, the TFR approach provides clock stability and constancy and increases the reliability and the availability of PTP systems. The performance of TFR has been analyzed and compared to that of the standard PTP. Various simulations were conducted to validate the performance analysis. The results show that, for our sample network, the TFR approach reduces clock drifting by 90% in comparison to the standard PTP, thus providing better clock firmness and synchronization accuracy for PTP clocks. Full article

The best master clock (BMC) algorithm is currently used to establish the master-slave hierarchy for the IEEE 1588 Precision Time Protocol (PTP). However, the BMC algorithm may create an unbalanced hierarchy that contains several boundary clocks with a large number of slaves in comparison to other clocks. The unbalanced hierarchy can cause problems, such as high communication load and high bandwidth consumption in boundary clocks. Additionally, the BMC algorithm does not provide any fast recovery mechanism in the case of a master failure. In this paper, we propose a novel balanced synchronization hierarchy with spare masters (BSHSM) algorithm to establish a balanced master-slave hierarchy and to provide a fast recovery mechanism in the case of master failures for the PTP. The BSHSM algorithm establishes the master-slave hierarchy with boundary clocks that have a balanced number of slaves. In doing so, it solves the problems caused by the unbalanced master-slave hierarchy. Additionally, the BSHSM algorithm provides a fast recovery mechanism by selecting a spare master for each boundary clock; this allows a boundary clock to immediately select a new master clock when its current master has failed or is disconnected. The fast recovery mechanism reduces the period of running freely and clock drift in clocks, improving the synchronization quality of the PTP. Various simulations were conducted using the network simulation OMNeT++ v4.6 to analyze, evaluate, and compare the performance of the BSHSM and BMC algorithms. The simulation results show that the synchronization hierarchy of the BSHSM algorithm is much more balanced than the BMC algorithm, and it also has a shorter period of recovery. Full article