Precision Time Protocol

About: Precision Time Protocol is a research topic. Over the lifetime, 604 publications have been published within this topic receiving 6006 citations. The topic is also known as: PTP & IEEE 1588.

Precision Time Protocol Prototype on Wireless LAN

Abstract: IEEE 1588 is a new standard for precise clock synchronization for networked measurement and control systems in LAN environment. This paper presents the design and implementation of an IEEE 1588 PC software prototype for Wireless LANs (WLAN). Accuracy is improved using two new developed methods for outbound latency estimation. In addition, an algorithm for adjusting the local clock is presented. The achieved accuracy is measured and compared between WLAN and fixed LAN environments. The results show that 2.8 μs average clock offset can be reached on WLAN, while wired Ethernet connection enables 2.5 μs.

Mitigation of Asymmetric Link Delays in IEEE 1588 Clock Synchronization Systems

Abstract: The IEEE 1588 standard defines the Precision Time Protocol (PTP) which provides mechanisms for synchronizing distributed clocks in packet-based networks. The accuracy of PTP synchronization depends on a number of factors such as the quality of the timestamps, packet delay variation, clock stability, and the asymmetry. In the latest update of the standard, IEEE 1588 version 2008, compensations for asymmetric delays have been introduced into the protocol. However, specific procedures for determining the asymmetry have not been specified. This paper analyzes various asymmetry mitigation measures for software timestamping and proposes a timestamp correction-based asymmetry compensation scheme. Measurements using WLAN synchronization hardware show that the proposed scheme can almost mitigate the link asymmetry without requiring any changes in PTP or additional messages.

ReversePTP: a software defined networking approach to clock synchronization

Abstract: We introduce ReversePTP, a novel approach to clock synchronization in Software Defined Networks (SDN). ReversePTP is based on the Precision Time Protocol (PTP), but is conceptually reversed; in ReversePTP all nodes (switches) in the network distribute timing information to a single node, the controller, that tracks the state of all the clocks in the network. Hence, all computations and bookkeeping are performed by the controller, whereas the `dumb' switches are only required to send it their current time periodically. In accordance with the SDN paradigm, the controller is the 'brain', making ReversePTP flexible and programmable from an SDN programmer's perspective.

IEEE 1588 High Accuracy Default Profile: Applications and Challenges

Abstract: Highly accurate synchronization has become a major requirement because of the rise of distributed applications, regulatory requests and position, navigation and timing backup needs. This fact has led to the development of new technologies which fulfill the new requirements in terms of accuracy and dependability. Nevertheless, some of these novel proposals have lacked determinism, robustness, interoperability, deployability, scalability or management tools preventing them to be extensively used in real industrial scenarios. Different segments require accurate timing information over a large number of nodes. Due to the high availability and low price of global satellite-based time references, many critical distributed facilities depend on them. However, the vulnerability to jamming or spoofing represents a well-known threat and back-up systems need to be deployed to mitigate it. The recently approved draft standard IEEE 1588-2019 includes the High Accuracy Default Precision Time Protocol Profile which is intensively based on the White Rabbit protocol. White Rabbit is an extension of current IEEE 1588-2008 network synchronization protocol for sub-nanosecond synchronization. This approach has been validated and intensively used during the last years. This paper revises the pre-standard protocol to expose the challenges that the High Accuracy profile will find after its release and covers existing applications, promising deployments and the technological roadmap, providing hints and an overview of features to be studied. The authors review different issues that have prevented the industrial adoption of White Rabbit in the past and introduce the latest developments that will facilitate the next IEEE 1588 High Accuracy extensive adoption.

System level tests of transformer differential protection using an IEC 61850 process bus

Abstract: The IEC 61850 family of standards for substation communication systems were released in the early 2000s, and include IEC 61850-8-1 and IEC 61850-9-2 that enable Ethernet to be used for process-level connections between transmission substation switchyards and control rooms. This paper presents an investigation of process bus protection performance, as the in-service behavior of multi-function process buses is largely unknown. An experimental approach was adopted that used a Real Time Digital Simulator and 'live' substation automation devices. The effect of sampling synchronization error and network traffic on transformer differential protection performance was assessed and compared to conventional hard-wired connections. Ethernet was used for all sampled value measurements, circuit breaker tripping, transformer tap-changer position reports and Precision Time Protocol synchronization of sampled value merging unit sampling. Test results showed that the protection relay under investigation operated correctly with process bus network traffic approaching 100% capacity. The protection system was not adversely affected by synchronizing errors significantly larger than the standards permit, suggesting these requirements may be overly conservative. This 'closed loop' approach, using substation automation hardware, validated the operation of protection relays under extreme conditions. Digital connections using a single shared Ethernet network outperformed conventional hard-wired solutions.