A Survey of Clock Synchronization Over Packet-Switched Networks

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

Research on Mobile Network High-precision Absolute Time Synchronization based on TAP

With the development of mobile communication and industrial internet technologies, the demand for robust absolute time synchronization based on network for diverse scenarios is significantly growing. TAP is a novel network timing method that aims to achieve sub-microsecond synchronization over air interface. This paper investigates the improvement and end-to-end realization of TAP. This paper first analyzes the effectiveness and deficiencies of TAP by establishing an equivalent clock model which evaluates TAP from timing error composition and allan variance. Second, this paper proposes a detailed base station and terminal design and the corresponding improvement of TAP. Both hardware compensation and protocol software design are taken into account so as to minimize timing error and system cost while maximizing compatibility with 3GPP. Finally, this paper presents a TAP end-to-end 5G prototype system developed based on software defined radio base station and COTS baseband module. The field test results show that the proposed scheme effectively solves the problems of TAP in application and robustly achieves 200ns level timing accuracy in various situations. The average accuracy with long observations can reach 1 nanosecond. It is 2$\sim$3 orders of magnitude better than common network timing methods, including NTP, PTP and the original TAP

The Impact of Network Latency on the Synchronization of Real-World IEEE 1588-2008 Devices Using 1588 and non-1588 Aware Switches

Precision Time Protocol (PTP) is a high precision time synchronization protocol designed to operate over a local area network. PTP, often referred to as 1588, is defined by the IEEE Standard 1588(TM)-2008. The protocol theoretically allows synchronization at the nanosecond level. New devices with support for 1588 are emerging into the market, but there have been few studies on real 1588 devices. Our research was broken into two parts: Phase 1 and Phase 2. Phase 1 studied performance of the protocol in an environment where two 1588 devices are connected via a network in which impairments that are typically observed in real networks are introduced and non-1588 devices are present. Measuring the Pulse-Per-Second (PPS) clock outputs of the 1588 boards, we were able to calculate the standard deviation and the mean synchronization error of the 1588 clocks. When we applied latency via network emulators and traffic generators between the 1588 connections, we found that 1588 boards were unable to maintain high accuracy time synchronization under variable and asymmetric latency. The results provide valuable insight into the real-world accuracy and robustness because it is rare that a network will contain neither variable or asymmetric latency. In Phase 2 we studied the impact of latency and high-bandwidth background traffic on 1588 clock synchronization when connected through 1588 and non-1588 aware switches. We found that 1588 aware switches provide higher precision time synchronization in small networks; but in large networks where congestion is present 1588 aware switches were unable to maintain high accuracy clock synchronization without prioritization. Our results also show that having cut-through Enterprise Ethernet switches connected to high congestion endpoints with priorities enabled is adequate for maintaining sub-microsecond synchronization performance

Building distributed sensor network applications using BIP

International audienceThe exponential increase in the demands for the deployment of large-scale sensor networks, makes the efficient development of functional applications necessary. Nevertheless, the existence of scarce resources and the derived application complexity, impose significant constraints and requires high design expertise. Consequently, the probability of discovering design errors, once the application is implemented, is considerably high. To address these issues, there is a need for the availability of early-stage validation, performance evaluation and rapid prototyping techniques at design time. In this paper we present a novel approach for the co-design of mixed software/hardware applications for distributed sensor network systems. This approach uses BIP, a formal framework facilitating modeling, analysis and implementation of real-time embedded, heterogeneous systems. Our approach is illustrated through the modeling and deployment of a Wireless Multimedia Sensor Network (WMSN) application. We emphasize on its merits, notably validation of functional and non-functional requirements through statistical model-checking and automatic code generation for sensor network platforms

A Beaconless Asymmetric Energy-Efficient Time Synchronization Scheme for Resource-Constrained Multi-Hop Wireless Sensor Networks

The ever-increasing number of WSN deployments based on a large number of battery-powered, low-cost sensor nodes, which are limited in their computing and power resources, puts the focus of WSN time synchronization research on three major aspects, i.e., accuracy, energy consumption and computational complexity. In the literature, the latter two aspects have not received much attention compared to the accuracy of WSN time synchronization. Especially in multi-hop WSNs, intermediate gateway nodes are overloaded with tasks for not only relaying messages but also a variety of computations for their offspring nodes as well as themselves. Therefore, not only minimizing the energy consumption but also lowering the computational complexity while maintaining the synchronization accuracy is crucial to the design of time synchronization schemes for resource-constrained sensor nodes. In this paper, focusing on the three aspects of WSN time synchronization, we introduce a framework of reverse asymmetric time synchronization for resource-constrained multi-hop WSNs and propose a beaconless energy-efficient time synchronization scheme based on reverse one-way message dissemination. Experimental results with a WSN testbed based on TelosB motes running TinyOS demonstrate that the proposed scheme conserves up to 95% energy consumption compared to the flooding time synchronization protocol while achieving microsecond-level synchronization accuracy.Comment: 12 pages, 16 figure

Study and Design of Inter-Range Instrumentation Group Time Code B Synchronization of IEC 61850 Sampled Values

Distribution substations are an important part of a chain which delivers energy from power production to customers. They transform the voltage level from transmission levels, usually 35kV and up, to distribution levels ranging between 600 and 35000 V. Recent developments in the instrument transformer field have been toward low-power solutions which use digital measurement values called sampled values in place of analog voltages and currents in substations. The IEC 61850-9-2 standard and its implementation guideline 9-2 LE by the UCA international users group define an interface for sampled values. This interface is used between an IED and LPIT. The main requirement of using sampled values is accurate time synchronization in order to prevent phase misalignment resulting in unnecessary protection function tripping. 9-2 LE defines two methods for synchronization: 1PPS and PTP. Today, PTP is widely used in the western markets, but due to costs associated with PTP-capable GPS clocks and Ethernet switches as well as vendor inoperability problems, some markets are hesitant to take into use. The purpose of this thesis is to propose a solution to this problem: use IRIG-B as a synchronization method in a PTP grandmaster. This paper discusses the differences between these two time synchronization topologies, associated costs, disturbance handling, accuracy and it also discusses the design of IRIG-B to PTP conversion done in a bay-level device. The device acts as a PTP grandmaster but the source comes from an IRIG-B clock instead of a GPS PTP grandmaster clock. The results shown in this thesis demonstrate that using IRIG-B as a main or redundant source in synchronization of sampled values is a more cost-effective option, especially if the station is to be retrofitted with sampled values configuration. The proposed bay level device also maintains the desired accuracy levels of ±1 µs set by IEC 61850-5.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Current Implementation of the Flooding Time Synchronization Protocol in Wireless Sensor Networks

Time synchronization is an issue that affects data accuracy within wireless sensor networks (WSNs). This issue is due to the complex nature of the wireless medium and can be mitigated with accurate time synchronization. This research focuses on the Flooding Time Synchronization Protocol (FTSP) since it is considered as the gold standard for accuracy in WSNs. FTSP minimizes the synchronization error by executing an algorithm that creates a unified time for the network reporting micro-second accuracy. Most synchronization protocols use the FTSP implementation as a benchmark for comparison. The current and only FTSP implementation runs on the TinyOS platform and is fully available online on GitHub. However, this implementation contains flaws that make micro-second accuracy impossible. This study reports a complete FTSP implementation that achieves micro-second accuracy after applying modifications to the current implementation. The new implementation provides a new standard to be used by future researches as a benchmark