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.

Asymmetry Mitigation in IEEE 802.3 Ethernet for High-Accuracy Clock Synchronization

Abstract: Clock synchronization is one of the basic services in a distributed network as it enables a palette of services, such as synchronized measurements and actions, or time-based access to shared communication media. The IEEE 1588 standard defines the precision time protocol (PTP) that is capable of synchronizing multiple slave clocks to a master by means of synchronization event messages. Supported by the recent advances in hardware timestamping, PTP devices are ready for achieving synchronization accuracies in the subnanosecond range. The accuracy of practical synchronization systems is, however, often bounded by the inability to determine and compensate for asymmetric line delays leading to unresolvable clock offsets. Although IEEE 1588 version 2008 is able to compensate for known asymmetry, no specific measures to estimate the asymmetry are defined in the standard. In this paper, we present a solution to determine the asymmetry for 100Base-TX networks based on line swapping and highly accurate timestamping. When the presented approach is used within the startup procedure of an Ethernet link, the synchronization offsets can be minimized while the operation of the network is not impaired. We show by an FPGA-based prototype system that our approach is able to reduce the clock offset from multiple nanoseconds to below 120 ps.

An implementation of IEEE 1588 protocol for IEEE 802.11 WLAN

Abstract: Clock synchronization is one of the enabling technologies for Wireless Local Area Networks (WLAN). It is crucial to perform applications such as data fusion, location detection and energy conservation. IEEE 1588 Precision Time Protocol (PTP) is a widely used clock synchronization protocol, but its accuracy is affected by bidirectional asymmetric delays in WLAN. A detailed analysis of the generation mechanism and statistical properties of the bidirectional asymmetric delays in IEEE 802.11 WLAN is conducted firstly. Then, a Kalman filter is designed for delay filtering. And based on the Kalman filter, a clock servo system is proposed using pure software-based implementation of PTP for IEEE 802.11 WLAN. Finally, the effectiveness of the implementation is verified by experiments. Experimental results show that the implementation has the virtues of high synchronization accuracy, short convergence time and small deviation error.

Precision timing in the NEPTUNE Canada network

Abstract: Delivery of accurate timing to subsea instruments is one of the essential functions of the NEPTUNE Canada ocean observatory. In the context of an ocean observing system, “timing” is understood to mean the ability to timestamp data using a clock which is traceable to Universal Time Coordinates (UTC) within some desired level of precision. Transmission or delivery of timing means transporting the necessary timing signals and data to subsea instruments or data collection processors. Timing signals are conventionally delivered in the form of a logic state transition on a dedicated communications line followed by a data string indicating the time at which the transition occurred. NEPTUNE Canada employs Ethernet communications channels to deliver timing. This avoids the need to provision additional communications channels and ensure that timing signals are available at all points within the network. The disadvantage of this approach is that timing signals must share the communications channels on which data is transmitted and may suffer delays or packet loss. Three timing protocols are employed: Network Time Protocol (NTP) described in IETF RFC 1305, Simple Network Time Protocol (SNTP) as described in RFC 2030 and IEEE 1588 Precision Time Protocol (PTP) per IEEE 1588. NTP/SNTP are generally accepted to be accurate to within a few milliseconds and are suitable for a wide variety of applications. PTP provides significantly better accuracy which is required for applications such as seismology and acoustic thermography. Master clocks located in the shore station acquire time from the Global Positioning System for transmission to subsea instruments. Alcatel-Lucent Submarine Networks and NEPTUNE Canada have successfully demonstrated PTP operation on a test bed which is representative of the NEPTUNE Canada network under simulated data traffic conditions, achieving a precision of ±10 microseconds or better. Ongoing development of IEEE 1588 will allow precision to within 100s of nanoseconds in future observatories. Science instruments which can take advantage of PTP timing delivery are currently under development.

Interworking agent adapted to interact between network and precision time protocol entities

Abstract: The embodiments of the present invention refer to an interworking agent aimed at being installed in a network node comprising a Precision Time Protocol “PTP” module, said agent comprising: a synchronization-side interface configured to measure Precision Time Protocol “PTP” metrics for detecting a Precision Time Protocol “PTP” signal failure, read and modify Precision Time Protocol “PTP” parameters of the Precision Time Protocol “PTP” module, at least one network-side interface configured to measure network metrics for selecting the optimal path for packet synchronization signals monitor network events for detecting a network path change, read and modify signals exchanged with a network planning entity and, signals exchanged between network nodes at the network level in order to communicate with remote interworking agents located in other network nodes.

Method and devices for time and frequency synchronization

Abstract: This invention relates to methods and devices for time and frequency synchronization, especially over packet networks using, for example, the IEEE 1588 Precision Time Protocol (PTP). Timing protocol messages are exposed to artifacts in the network such as packet delay variations (PDV) or packet losses. Embodiments of the invention provide a recursive least squares mechanism for clock offset and skew estimation. A major potential advantage of such estimation is that it does not require knowledge of the statistics of the measurement noise and process noise. An implementation using a digital phase locked loop based on direct digital synthesis to provide both time and frequency signals for use at the slave (time client) is also provided.