24 research outputs found
A Survey on IEEE 1588 Implementation for RISC-V Low-Power Embedded Devices
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.This work was partially supported by the ECSEL Joint Undertaking in the H2020 project IMOCO4.E, grant agreement No.10100731, and by the Basque Government within the fund for research groups of the Basque University System IT1440-22 and KK-2023/00015
Nanosecond-Level Resilient GNSS-Based Time Synchronization in Telecommunication Networks Through WR-PTP HA
In recent years, the push for accurate and reliable time synchronization has gained momentum in critical infrastructures, especially in telecommunication networks, driven by the demands of 5G new radio and next-generation technologies that rely on submicrosecond timing accuracy for radio access network (RAN) nodes. Traditionally, atomic clocks paired with global navigation satellite systems (GNSS) timing receivers have served as grand master clocks, supported by dedicated network timing protocols. However, this approach struggles to scale with the increasing numbers of RAN intermediate nodes. To address scalability and high-accuracy synchronization, a more cost-effective and capillary solution is needed. Standalone GNSS timing receivers leverage ubiquitous satellite signals to offer stable timing signals but can expose networks to radio-frequency attacks due to the consequent proliferation of GNSS antennas. Our research introduces a solution by combining the white rabbit precise time protocol with a backup timing source logic acting in case of timing disruptive attacks against GNSS for resilient GNSS-based network synchronization. It has been rigorously tested against common jamming, meaconing, and spoofing attacks, consistently maintaining 2 ns relative synchronization accuracy between nodes, all without the need for an atomic clock
Ethernet-based timing system for accelerator facilities: The IFMIF-DONES case
This article presents the design of a timing system for accelerator facilities, which relies on a general networking
approach based on standard Ethernet protocols that keeps all the devices synchronized to a common time
reference. The case of the IFMIF-DONES infrastructure is studied in detail, providing a framework for the
implementation of the timing system. The network time protocol (NTP) with software timestamping and the
precision time protocol (PTP) with hardware timestamping are used to synchronize devices with sub-millisecond
and sub-microsecond accuracy requirements, respectively. The design also considers the utilization of IEEE 1588
high accuracy default PTP profile (PTP-HA) to provide sub-nanosecond accuracy for the most demanding
components. Three different solutions for the design of the timing system are discussed in detail. The first solution
considers the deployment of one time-dedicated network for each synchronization protocol, while the
second one proposes the integration of the synchronization data of NTP and PTP into the networks of the facility.
The third solution relies on the single distribution of PTP-HA to all the systems. The final design aims to be fully
based on standard technologies and to be cost-efficient, seeking for interoperability and scalability, and minimizing
the impact on other systems in the facility. An experimental setup has been implemented to evaluate and
discuss the suitability of the solutions for the timing system by studying the synchronization accuracy obtained
with NTP, PTP and PTP-HA under different network conditions. It includes a timing evaluation platform that
tries to resemble the network architecture foreseen in the facility. The measured results revealed that PTP is the
most limiting protocol for the second solution. Using the default PTP configuration, it tolerates less than 20% of
maximum bandwidth utilization for symmetric bidirectional flows, and around 30% in the case of unidirectional
flows (server to client or client to server), with the current setup and using switches without enabled timing
support. This case study provides a better understanding of the trade-off between bandwidth utilization, synchronization
accuracy and cost in these kinds of facilities
Time Sensitive Networking over 5G Networks
Time-Sensitive Networking (TSN IEEE 802.1Q), is an Ethernet technology that provides deterministic messaging on standard Ethernet. When centrally managed, the TSN technology offers the capability of guaranteed delivery of messages with reduced jitter. TSN uses time-scheduling in providing deterministic communications and works at Layer 2 (L2) of the Open System Interconnection. The advantage of TSN working at L2 is that TSN entities (switches and bridges) only need the information contained in Ethernet headers to make forwarding decisions. In addition, the information carried in Ethernet frame payloads does not have to be limited to IP only, making TSN applicable in industrial applications with different application payloads.
The goal of the thesis was to come up with a state-of-the-art design of IEEE TSN modules. This goal involved designing a topology for testing TSN, prototyping the TSN modules, and testing the modules when completed. The thesis evaluates how the developed TSN module's performance compares to IEEE WG set standards.
I carried out the experimentation based on the IEEE Working Group (WG) recommendations and publications which provided the necessary modifications to Precision Time Protocol version 2 (PTPv2) regarding packets that needed to be modified to develop generalized Precision Time Protocols (gPTP). Before entering and exiting the 5G System (5GS), the gPTP messages are changed. These encompass all the needed packet header modifications and necessary calculations to achieve the synchronization accuracies of 900 nanoseconds as stipulated by the IEEE 802.1AS standard.
The project's findings were that the functionalities stipulated by the IEEE TSN WG were possible to implement and even achieve synchronization between the different TSN modules. The thesis did not accomplish the synchronization accuracy levels specified by the IEEE TSN. This low synchronization accuracy level was understandable, considering that the 5GS and equipment needed to improve performance were missing. The thesis evaluates the exactness with which gPTP packets arriving at the TSN modules could be detected, captured, modified, and sent to end stations successfully and provides an in-depth explanation for why the synchronization accuracy levels achieved were low
A Comprehensive Review on Time Sensitive Networks with a Special Focus on Its Applicability to Industrial Smart and Distributed Measurement Systems
The groundbreaking transformations triggered by the Industry 4.0 paradigm have dramati-cally reshaped the requirements for control and communication systems within the factory systems of the future. The aforementioned technological revolution strongly affects industrial smart and distributed measurement systems as well, pointing to ever more integrated and intelligent equipment devoted to derive accurate measurements. Moreover, as factory automation uses ever wider and complex smart distributed measurement systems, the well-known Internet of Things (IoT) paradigm finds its viability also in the industrial context, namely Industrial IoT (IIoT). In this context, communication networks and protocols play a key role, directly impacting on the measurement accuracy, causality, reliability and safety. The requirements coming both from Industry 4.0 and the IIoT, such as the coexistence of time-sensitive and best effort traffic, the need for enhanced horizontal and vertical integration, and interoperability between Information Technology (IT) and Operational Technology (OT), fostered the development of enhanced communication subsystems. Indeed, established tech-nologies, such as Ethernet and Wi-Fi, widespread in the consumer and office fields, are intrinsically non-deterministic and unable to support critical traffic. In the last years, the IEEE 802.1 Working Group defined an extensive set of standards, comprehensively known as Time Sensitive Networking (TSN), aiming at reshaping the Ethernet standard to support for time-, mission-and safety-critical traffic. In this paper, a comprehensive overview of the TSN Working Group standardization activity is provided, while contextualizing TSN within the complex existing industrial technological panorama, particularly focusing on industrial distributed measurement systems. In particular, this paper has to be considered a technical review of the most important features of TSN, while underlining its applicability to the measurement field. Furthermore, the adoption of TSN within the Wi-Fi technology is addressed in the last part of the survey, since wireless communication represents an appealing opportunity in the industrial measurement context. In this respect, a test case is presented, to point out the need for wirelessly connected sensors networks. In particular, by reviewing some literature contributions it has been possible to show how wireless technologies offer the flexibility necessary to support advanced mobile IIoT applications
The Virtual Bus: A Network Architecture Designed to Support Modular-Redundant Distributed Periodic Real-Time Control Systems
The Virtual Bus network architecture uses physical layer switching and a combination of space- and time-division multiplexing to link segments of a partial mesh network together on schedule to temporarily form contention-free multi-hop, multi-drop simplex signalling paths, or 'virtual buses'. Network resources are scheduled and routed by a dynamic distributed resource allocation mechanism with self-forming and self-healing characteristics. Multiple virtual buses can coexist simultaneously in a single network, as the resources allocated to each bus are orthogonal in either space or time. The Virtual Bus architecture achieves deterministic delivery times for time-sensitive traffic over multi-hop partial mesh networks by employing true line-speed switching; delays of around 15ns at each switching point are demonstrated experimentally, and further reductions in switching delays are shown to be achievable. Virtual buses are inherently multicast, with delivery skew across multiple destinations proportional to the difference in equivalent physical length to each destination. The Virtual Bus architecture is not a purely theoretical concept; a small research platform has been constructed for development, testing and demonstration purposes
On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks
Flow reshaping is used in time-sensitive networks (as in the context of IEEE
TSN and IETF Detnet) in order to reduce burstiness inside the network and to
support the computation of guaranteed latency bounds. This is performed using
per-flow regulators (such as the Token Bucket Filter) or interleaved regulators
(as with IEEE TSN Asynchronous Traffic Shaping). Both types of regulators are
beneficial as they cancel the increase of burstiness due to multiplexing inside
the network. It was demonstrated, by using network calculus, that they do not
increase the worst-case latency. However, the properties of regulators were
established assuming that time is perfect in all network nodes. In reality,
nodes use local, imperfect clocks. Time-sensitive networks exist in two
flavours: (1) in non-synchronized networks, local clocks run independently at
every node and their deviations are not controlled and (2) in synchronized
networks, the deviations of local clocks are kept within very small bounds
using for example a synchronization protocol (such as PTP) or a satellite based
geo-positioning system (such as GPS). We revisit the properties of regulators
in both cases. In non-synchronized networks, we show that ignoring the timing
inaccuracies can lead to network instability due to unbounded delay in per-flow
or interleaved regulators. We propose and analyze two methods (rate and burst
cascade, and asynchronous dual arrival-curve method) for avoiding this problem.
In synchronized networks, we show that there is no instability with per-flow
regulators but, surprisingly, interleaved regulators can lead to instability.
To establish these results, we develop a new framework that captures industrial
requirements on clocks in both non-synchronized and synchronized networks, and
we develop a toolbox that extends network calculus to account for clock
imperfections.Comment: ACM SIGMETRICS 2020 Boston, Massachusetts, USA June 8-12, 202
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