Development of improved and scalable calibration techniques for PTP-WR fibre links (Objective 1)

Fibre propagation asymmetry measurement techniques in the laboratory on testbeds were developed. Low-asymmetry links were tested in laboratory. Both fixed-wavelength transceivers and tuneable-transceivers have been tested. Data from laboratory tests on spools were collected, Single fibre calibration techniques were developed using fixed-wavelength or tuneable-wavelength transceivers. Calibration techniques were documented.

Work is documented on the open hardware website:

Field-tests for single-fibre propagation asymmetry calibration techniques were performed on the VTT Otaniemi-Metsähovi testbed (50km) and on the INRIM-LEONARDO connection. The links were set up and brought into operational within the project.

The calibration techniques developed in WRITE achieved a reliable and unprecedented level of better than 200 ps accuracy.

Even though the COVID-19 pandemic outbreak slowed down field and laboratory activities, the consortium set up calibration test for the electro-optic components of the time dissemination devices, assessing a metrological validation of the WRITE methods at the interlaboratory level.

This objective was successfully achieved.

Development of validated techniques for redundant and resilient PTP-WR time transfer to industrial end users (Objective 2)

WRITE identified topologies for redundant WR networks. Parallel and ring topologies are acceptable solutions. The scalability was evaluated for WR-PTP in parallel networks using WR-PTP switches in different configurations: boundary clock, transparent clock and hybrid clock. The requirements for system holdover have been identified for several industrial domains (power grid, electrical substations, synchro phasor, etc).

Two reliability mechanisms for WR-PTP network solutions were identified: holdover and switchover. For switchover of the WR-PTP switch, two possible mechanisms have been identified: (i) Best Master Clock Algorithm (BMCA): not seamless (20 seconds recovery), and (ii) Seamless switchover: hot-swap between several references. From these two options, only the BMCA was developed in this project, because this approach was in line with the existing IEEE 1588 standard. A prototype version of a BMCA was tested and will be included in the next formal release of the WR firmware beyond this project (more info at

Holdover mechanisms in case of loss of the link to the WR grandmaster were identified using either an oven-controlled crystal oscillator (OCXO) in the WR main loop or using an internal expansion board with a suitable oscillator or using 1PPS/10MHz reference signals from an external reference clock. An evaluation of an OCXO in the WR main loop was made with and without hold-over capabilities implemented in the software.

Redundant WR links have been implemented into new firmware releases of WR switches. In particular, concerning the resilience targets, a hold-over oscillator solution has been developed together with an update of the WR switch firmware for supporting different types of hold-over oscillators, responding to different requirements, i.e. the tolerable level of accuracy after few hours and up to one day. That level typically spans from 100 ns up to 1 microsecond (finance, aerospace, telecommunications) or even up to hundreds of microseconds (electronic manufacturers).

For the first time, a systematic analysis for PTP-WR redundancy and resilience has been made, targeting the needs of industrial users. 

This objective was successfully achieved.

Development of a next generation of PTP-WR devices with improved performance and high-compatibility interfacing with industrial applications (Objective 3)

The consortium completed the analysis of single components to be improved, to increase the overall performances of WR-PTP devices. In particular, WRITE tested alternative Local Oscillators and as a result, the new design of the board progressed well. Different WR platforms have been compared, completing the design and realisation of a new SPEC 7 board (KINTEX). Tests on the board by different partners ensured repeatability and reproducibility, thanks to a strong collaborative attitude in the the consortium.

New low jitter circuitry has been realised. The data and designs from all the activities are accessible via the WR open hardware repository ( The Local Oscillator (LO) in existing hardware has been improved, with a full review and a complete laboratory test of alternative LOs for PTP-WR hardware. An external servo loop circuit for the improved LO has been designed, realised and optimised, and the new LO is available for the hardware technology SPEC 7. In addition, a low noise power supply as well as a new 4x output distribution unit have been developed and realised.

Twelve SPEC7 boards (Zynq-7000) were produced, and they have been assessed at CERN, INRIM, VTT, NPL and NWO-I. SPEC7 sources are now merged into the main branch of the WR open hardware repository. This is a fruitful collaboration among partners of the consortium but also relevant stakeholders such as CERN.

A High Precision Oscillator (HPSEC) was designed and tested, and a Low-Jitter WR switch has been developed.

All the new hardware developed in the project took a step beyond previous state of the art, and for the first time a stability of 6×10-15 in terms of fractional frequency Allan deviation has been achieved, together with an accuracy at 200 ps level.

This objective was successfully achieved.

Demonstration of the use of PTP-WR to deliver UTC(k) time scales and frequency in the RF domain from NMIs to industrial users and evaluation of the end-to-end uncertainty of the established time transfer (Objective 4)

The architecture of four testbeds has been developed, and these four testbeds have been assessed and are now established in Italy, the Netherlands, France, and Sweden.

COVID-19 pandemic outbreak severely impacted field activities, however the partners have managed to deliver project activities despite these delays.

In France, OBSPARIS and Thales AVS established the link over a distance of the order of 50 km. WR is implemented on a dark fibre, even though DWDM architecture is present, resulting in a valuable flexibility of this link for future testing.

In Italy, INRIM and LEONARDO completed the link (230 km) disseminating UTC (IT). The link is realised by DWDM multiplexing, and a coherent time and frequency transfer is also present on the same fibre. LEONARDO used the link to evaluate the performance and the absolute frequency of their local commercial clocks (Hydrogen Masers), as part of their production line. The link is under continuous operation, and it will be kept under operation also after the end of WRITE project.

In the Netherlands, VSL and OPNT installed a link from VSL to Amsterdam, close to potential customers. The link is currently under operation, disseminating UTC (VSL).

Additionally, the two established WR links to NETNOD AB in the Stockholm area have been operated and characterised, UTC (SP) is disseminated.

This objective was successfully achieved.



M36 Progress Meeting

23 Nov 2021

The final consortium meeting to assess WRITE progress was held online.

M27 Progress Meeting

23 Dec 2020

A consortium meeting to assess WRITE progress at month 27 was held online.

M18 Progress Meeting

12-13 Dec 2019

A consortium meeting to assess WRITE progress at month 18 was held at Seven Solutions, Spain.

M9 Progress Meeting

11-12 March 2019

A consortium meeting to assess WRITE progress at month 9 was held at NIKHEF, Amsterdam.

Euramet Technical Committee for Time and Frequency

7-8 March 2019

Dr. Anders Wallin presented WRITE on behalf of the Consortium at the  Euramet Technical Committee for Time and Frequency meeting  at NPL, Teddington.

WP1 Calibration Bootcamp

12–16 November 2018

WP1 Calibration Bootcamp

Attendees gained hands-on experience with the calibration devices and other instruments required for White Rabbit calibrations. It was discussed how calibration devices and setups could be replicated by the other WRITE partners in their home laboratories. The documentation of calibration techniques (WP1 deliverable) was started. WRITE participants from VTT, INRiM, NPL, 7Sols and OPNT attended the bootcamp.

A hands-on ‘calibration bootcamp’ took place at Nikhef in Amsterdam on 12–16 November 2018. The motivation was to transfer knowledge that Nikhef has on absolute calibration and delay-propagation calibration to other (mainly WP1) WRITE partners.

10th White Rabbit Workshop

6–7 October 2018

The 10th WR workshop was held at CERN, Geneva (Switzerland) on 6–7 October 2018.

Topics included WR technology evolution, applications and the process of standardisation under IEEE 1588.

View full meeting report