The WRITE (White Rabbit for Industrial Timing Enhancement) Project Update

Time and frequency dissemination for industrial applications is still predominantly realised through radio signals and satellite time broadcasting, such as the widely used Global Positioning System (GPS). However, the weak signal power received on Earth from GPS and other Global Navigation Satellite Systems (GNSS) represents a significant threat to their integrity and resilience since they are vulnerable to jamming, spoofing, and disruption by space weather events. There is therefore considerable motivation to progress beyond GNSS-based time and frequency dissemination techniques. However, any alternative time and frequency distribution technique must have a high degree of resilience with built-in redundancy. Moreover, in order to facilitate widespread and rapid uptake by industrial and commercial users, any alternative should possess a number of features: it should lend itself to standardization and be capable of practical interfacing with existing network infrastructures; it should be scalable and address a range of user requirements; and it should enable measurement traceability to the time standard Coordinated Universal Time (UTC). One potential alternative to satellite-based techniques for time and frequency distribution which meets these criteria is the White Rabbit (PTP-WR) protocol. This open-source technology provides sub-nanosecond accuracy and picosecond-level precision of synchronization over optical fibre, scalable to many nodes. The protocol is developed at CERN in collaboration with research organisations and companies, leading to rapid innovation and commercialisation opportunities. It has recently been integrated into the IEEE 1588 Precision Time Protocol (PTP) standard as IEEE 1588-2019 PTP High Accuracy, a significant achievement which will facilitate industry uptake. In June 2018, the White Rabbit for Industrial Timing Enhancement (WRITE) project was started with the aim of further developing the PTP-WR hardware, monitoring and calibration techniques. The project will demonstrate resilient, validated, precision time dissemination to industrial and commercial user testbeds, which will be UTC traceable. As of October 2020, the WRITE project has already made significant progress in improving PTP-WR methods and devices, validating some techniques on in-field deployments. Four testbeds have been established, designed to demonstrate UTC(k) dissemination to industry partners alongside the ‘accuracy’, ‘precision’, ‘redundancy’ and ‘connectivity’ challenges identified by the project. Outreach activities such as a virtual Stakeholder workshop have facilitated the WRITE project engagement with end users in industry, research, NRENs (National Research and Education Networks) and metrology. As part of this project, new scalable calibration techniques have been developed for fibre propagation asymmetry, PTP-WR devices and SFPs. Calibration of each individual component of a PTP-WR link is required for interoperability of PTP-WR equipment from different manufacturers and replacement in the event of equipment failures. A system with calibrated components will in future lead to “plug-and-play” cost-effective time services to industry, replacing expensive in-situ end-to-end calibrations of each link. NPL are participating in this interoperability testing of a new PTP-WR device, using the White Rabbit Electrical Absolute Calibration technique. The WRITE project is also investigating network topologies and monitoring techniques to improve redundancy. Different hardware and software holdover mechanisms have been tested to improve resilience. Within this task, NPL are evaluating the PTP-WR holdover mechanism based on a commercial caesium clock.