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papers/ISPCS2018/wrApplicationsOverview.bib
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......@@ -274,13 +274,7 @@ author={E. F. Dierikx and et al.},
journal={IEEE T-UFFC},
title={White Rabbit Precision Time Protocol on Long-Distance Fiber Links},
year={2016},
volume={63},
number={7},
pages={945-952},
keywords={Global Positioning System;clocks;local area networks;optical fibre communication;protocols;time measurement;GPS precise point positioning;bidirectional paths;chromatic dispersion;delay asymmetry;distance 950 km;initial calibration;long-distance fiber links;synchronous Ethernet optical fiber networks;time transfer;white rabbit precision time protocol;Clocks;Delays;Optical fiber networks;Optical fibers;Optical switches;Synchronization;Clocks;White Rabbit;optical fiber networks;precision time protocol (PTP);time dissemination;timing},
doi={10.1109/TUFFC.2016.2518122},
ISSN={0885-3010},
month={July},}
}
@inproceedings{biblio:MIKES-50km,
author = "Anders Wallin and et al.",
......@@ -303,17 +297,14 @@ ISSN={},
month={April},}
@INPROCEEDINGS{biblio:SYRTE-LNE-500km,
author={N. Kaur and et al.},
author={Kaur, Namneet and Frank, Florian and Pottie, Paul-Erik and Tuckey Philip},
booktitle={EFTF/IFCS},
title={Time and frequency transfer over a 500 km cascaded White Rabbit network},
title={Time and frequency transfer over a 500 km cascaded {WR} network},
year={2017},
volume={},
number={},
pages={86-90},
keywords={atomic clocks;data acquisition;optical fibre communication;synchronisation;White Rabbit link;active telecommunication networks;cascaded White Rabbit network;commercial White Rabbit equipment;distance 500.0 km;frequency dissemination;frequency transfer stability;integration time;long distance optical fiber links;software parameters;time transfer stability;unidirectional link setup;Clocks;Optical switches;Rabbits;Temperature measurement;Thermal stability;Time-frequency analysis},
doi={10.1109/FCS.2017.8088808},
ISSN={},
month={July},}
}
@inproceedings{biblio:WR-ultimate-limits,
author = "Rizzi, Mattia and et al.",
......@@ -553,3 +544,7 @@ year = "2016",
@Misc{biblio:WRITE,
title = "{{WRITE}: White Rabbit Industrial Timing Enhancement (SRT-i26: Selected Research Topic, was JRP-i26)}",
}
@Misc{biblio:SPEV7,
title = "{Simple PCIe FMC carrier 7}",
howpublished = {\url{www.ohwr.org/projects/spec7/wiki/}},
}
papers/ISPCS2018/wrApplicationsOverview.tex
View file @ 3ad00fd9
......@@ -50,20 +50,20 @@
\begin{abstract}
%\boldmath
This article provides an overview of applications and
This article provides a non-exhaustive overview of applications and
enhancements to the White Rabbit (WR) extension of the Precision Time Protocol (PTP).
Initially developed to serve accelerators at the European Organization for
Nuclear Research (CERN), WR has become widely-used synchronization solution
in scientific installations. This article classifies WR applications
into five types, briefly explains each and describes its example
installations. It summarizes WR enhancements that have been triggered by
installations. The article then summarizes WR enhancements that have been triggered by
different applications and outlines WR's integration into the PTP standard.
Finally, it concludes that WR applications will continue to proliferate in
science and should soon find its way into the industry.
Based on the presented variety of WR applications and enhancement, it concludes
that WR will continue to proliferate in scientific applications and should soon find its way into the industry.
\end{abstract}
\vspace{-0.4cm}
\vspace{-0.1cm}
\section{Introduction}
White Rabbit (WR) \cite{biblio:whiteRabbit} is a new technology that provides sub-nanosecond
accuracy and picoseconds precision of synchronization as well as deterministic and
......@@ -127,7 +127,7 @@ collaboration with companies.
% This article attempts at providing a snapshot of the various WR applications,
% the ongoing work on enhancing WR and evolution of WR into IEEE1588.
The article briefly describes in Section~\ref{sec:wrElements} the portfolio of
available WR network elements. It then explains in
readily available WR network elements. It then explains in
Sections~\ref{sec:time-and-freq}-\ref{sec:RFoverWR} different types of
WR applications, their concept and use examples,
summarized in Table~\ref{tab:applications}. Application-triggered enhancements are described in
......@@ -218,7 +218,7 @@ EPFL & Switzerland & TS & 1km & 2/1/1
\label{sec:wrElements}
WR network elements, nodes and switches, are openly available on the Open Hardware Repository (OHWR)
\cite{biblio:OHWR} and can be purchased from companies. %, see Figure~\ref{fig:WRN}.
\cite{biblio:OHWR} and can be purchased from companies \cite{biblio:WRcompanies}. %, see Figure~\ref{fig:WRN}.
While all of the WR networks use the same design of
the WR switch \cite{biblio:wr-switch},
the design of WR nodes depends on the application. Therefore the WR node design is made available
......@@ -354,8 +354,7 @@ and can be improved to 1e-12 without any modifications to the WR-PTP Protocol, s
Section~\ref{sec:JitterAndStability} and
\cite{biblio:MIKES-50km}\cite{biblio:SYRTE-LNE-500km}\cite{biblio:WR-ultimate-limits}.
Many of the National Time Laboratories are now working together with other WR users
and companies within the EU-founded projects to make prepare WR for industrial applications
\cite{biblio:WRITE}.
and companies within the EU-founded project WRITE \cite{biblio:WRITE} to prepare WR for industrial applications.
% At CERN, the General Machine Timing controller of the Antiproton Decelerator (AD)
% is synchronized with WR link to a similar controller of the LHC Injection
% Chain (LHC) that provides the beam also for AD. Such a WR link provides traceability
......@@ -427,8 +426,8 @@ WR-based GMT has replaced the previously used system for the existing GSI
accelerators and will control GSI's new Facility for Antiproton and Ion Research
(FAIR) \cite{biblio:GSI-WR-GMT}. Control of GSI and FAIR requires that the
control-information is delivered from a common controller to any of the controlled
subsystems in any of the accelerators within 500$\mu$s. The most demanding of
these subsystems require an accuracy of 1-5ns. The controller, called Data Master,
subsystems in any of the accelerators within 500~$\mu$s. The most demanding of
these subsystems require an accuracy of 1-5~ns. The controller, called Data Master,
is a WR node. The subsystems are either WR nodes or have a direct interface with WR Nodes.
All these WR nodes are connected to a common WR network that provides synchronization,
delivers control-information from the Data Master to all subsystems as well as
......@@ -455,7 +454,7 @@ conception and it is yet to be implemented at CERN.
% China Spoliation Neutron Source (CSNS)\\
% General Machine Timing (GMT) and Beam Synchronous Timing (BST)\\
% \newpage
\newpage
\section{Precise Timestamping (TS)}
\label{sec:timestamping}
% \subsection{Basic Concept}
......@@ -471,9 +470,9 @@ measure the time of flight (ToF) or correlate events between distributed systems
% precision and frequency stability are required. %, accuracy is not so important.
Precise timestamping is one of the most widely-used applications of WR.
The ability
to timestamp input signals and send them over WR network to a standard PC for
to timestamp input signals and send these timestamps over WR network to a standard PC for
analysis proves to be an extermely convenient solution to many otherwise
challenging measurements.
challenging distributed measurements.
% \subsection{Example Applications}
......@@ -496,7 +495,7 @@ in the time of arrival, the trajectory of particles are calculated. For these
applications, a high precision and accuracy is required in harsh
environmental conditions due to their locations \cite{biblio:TAIGA-WR-harsh-env}.
The Large High Altitude Air Shower Observatory (LHAASO), located at 4410m above
The Large High Altitude Air Shower Observatory (LHAASO), located at 4410~m above
sea level in China (Tibert), requires a 500~ps RMS \cite{biblio:LHAASO} alignment
of timestamps produced by 7000 WR nodes distributed over 1~km$^2$ and exposed to
day-night variation of -10 to +55 degrees Celsius. To meet such requirements, active
......@@ -652,14 +651,14 @@ The original BTrain system uses coaxial cables to distribute pulses that indicat
increase and decrease of the B-value. This method is now being upgraded to a
WR-based distribution of the absolute B-value and additional information
\cite{biblio:WR-Btrain-MM}. In this upgraded system B-values are transmitted
at 250kHz (every $4\mu$s) from the measurement WR node to all the other WR nodes
at 250~kHz (every $4\mu$s) from the measurement WR node to all the other WR nodes
that are integrated with RF cavities, power converters and beam instrumentation. In the most
demanding accelerator, SPS, the data must be delivered over 2 hops (WR switches)
with latency of $10\mu s\pm 8ns$.
The WR-BTtrain has been successfully evaluated in the PS accelerators where it has
been running operationally since 2017 \cite{biblio:WR-BTrain-RF}. By 2021, all
the accelerators should be running WR-BTrain operationally \cite{biblio:WR-Btrain-status}.
the CERN accelerators, except LHC, should be running WR-BTrain operationally \cite{biblio:WR-Btrain-status}.
% For each accelerator, a separated WR-BTrian system is installed consisting of 1-2
% WR switches and 2-5 WR nodes.
......@@ -685,12 +684,12 @@ WR slave nodes. In such schema, depicted in Figure~\ref{fig:RFoverWR} and detail
\label{fig:RFoverWR}
\end{figure}
a digital direct synthesis (DDS) based on the WR reference clock
signal (125MHz) is used to generate an RF signal. The generated RF signal is then compared by a phase detector to the
signal (125MHz) is used to generate an RF signal in the WR master node. The generated RF signal is then compared by a phase detector to the
input RF signal. The error measured by the phase detector is an input to a
loop filter (e.g. Integral-Proportional controller) that steers the DDS to produce a signal identical
to the RF input - effectively the DDS is locked to the input signal.
The tuning words of the DDS are the digital form of the RF input
that is sent over WR network. Each of the receiving WR nodes recreates the RF input signal
that is sent over WR network. Each of the receiving WR slave nodes recreates the RF input signal
by using the received tuning words to control the local DDS with a fixed delay.
In such way, the WR slave nodes produce RF outputs that are syntonized with
the RF input, phase-aligned among each other, and delayed with respect to the RF input --
......@@ -722,7 +721,7 @@ frequencies.
The radio-frequency transfer in CERN's Super Proton Synchrotron (SPS)
accelerator is also being upgraded to use WR. The SPS requires distribution
of a 200~MHz RF signal with 0.25ps RMS jitter (100Hz to 100kHz) and an accuracy of $\pm$10ps.
These requirements necessitate enhancements of WR performance.
These requirements necessitate enhancements of WR.
% \section{WR Applications outside CERN}
% \label{sec:GSI-GMT}
......@@ -1149,7 +1148,8 @@ The improved WR Switches are now commercially available \cite{biblio:WR-LJD-swit
A high performance low-jitter WR node is developed for the SPS's RF transmission
achieving jitter of sub-100fs RMS from 100Hz to 20MHz \cite{biblio:SPS-WR-LLRF}.
A WR node \cite{biblio:SPEV7} to achieve stability of 1e-13 over 100 s is designed
within the WRITE project.
\subsection{Temperature Compensation}
\label{sec:}
......@@ -1162,11 +1162,11 @@ delays, considering links below 10~km (see next section).
These delays are usually calibrated for WR devices
\cite{biblio:wrCalibration} at a room temperature and assumed constant throughout
operation. Their variation however is linear with temperature and so an online
correction can be applied. It was developed for the LHAASO
correction can be applied. Such correction was developed for the LHAASO
experiment \cite{biblio:wr-cngs} that requires 500ps RMS
synchronization of 7000 WR nodes in harsh environmental. For temperatures between
-10 and 50 degrees Celsius, such correction reduces the
peak-to-peak variation from 700~ps to $<$150ps with a standard deviation $<$50~ps \cite{biblio:LHAASO-WR-temp}.
-10 and 50 degrees Celsius, the developed correction reduces the
peak-to-peak variation from 700~ps to $<$150~ps with a standard deviation $<$50~ps \cite{biblio:LHAASO-WR-temp}.
% This online compensation
% is used in LHAASO to ensure 500ps (rms)
......@@ -1182,13 +1182,13 @@ Links longer than 80~km require active amplifiers and/or unidirectional fibers.
This deteriorates accuracy due to an unknown asymmetry.
On the 137~km bidirectional link in the Netherlands \cite{biblio:MIKES+VSL},
dedicated optical amplifiers that work with bidirectional fibers are used in
an attempt to overcome these limitation. The tests so far have shown $<$8ns accuracy
while a new "in-site" calibration method developed at VLS is expected to calibrate
an attempt to overcome these limitation. The tests so far have shown $<$8~ns accuracy
while a new "in-site" calibration under development at VLS is expected to calibrate
out this asymmetry (over a 2x 137km link) to a few 0.1~ns or less \cite{biblio:VLS-WR-insite-calib}.
On the 950~km unidirectional link in Finland \cite{biblio:MIKES+VSL} , GPS precise point positioning
On the 950~km unidirectional link in Finland \cite{biblio:MIKES+VSL}, GPS precise point positioning
(PPP) was used to calibrate asymmetry and achieve $\pm$2~ns accuracy. This
method requires re-calibration after any disruption of the network. Laboratory
tests of a 500km WR connection using five cascaded WR devicies and four 125km unidirectional
tests of a 500~km WR connection using five cascaded WR devicies and four 125~km unidirectional
links showed a 2.5~ns peak-to-peak time error \cite{biblio:SYRTE-LNE-500km}.
\subsection{Link Asymmetry}
......@@ -1198,11 +1198,11 @@ WR estimates and compensates asymmetry of bidirectional links knowing the relati
between the wavelengths in the two directions. This relation, characterized by the \textit{alpha}
parameter, is calibrated at room temperature and assumed constant.
However, the variation of fiber temperature results in changes of the actual
\textit{alpha} (-0.12~ps/km/K for 1310/1490~nm and -0.05~ps/km/K for 1490/1550~nm)
\textit{alpha} (e.g -0.12~ps/km/K for 1310/1490~nm)
while the variation of WR nodes/switches temperature result in laser wavelength
variation, e.g. 17~ps/nm km for 1550 nm. These and other
variation( e.g. 17~ps/nm km for 1550 nm). These and other
effects analyzed in \cite{biblio:SKA-80km} are significant on long links and
can amount to over 5~ns inaccuracy for bidirectional link using 1490/1550nm
can amount to over 5~ns inaccuracy for bidirectional link using 1490/1550~nm
and exposed to 50 degrees Celsius temperature variation. The Square Kilometre Array (SKA) \cite{biblio:SKA}
radio telescope mitigates these effects to achieve $<$1~ns accuracy on 80~km links
by using DWDM SFP on ITU channels C21/C22 (1560.61/1558.98~nm) and combining them
......@@ -1260,18 +1260,19 @@ is described in \cite{biblio:WRin1588}.
\section{Conclusions}
\label{sec:conclusions}
The number of WR applications and their specifications (link lenght, synchronization
performance) have exceeded the original requirements of the project.
This profileration of applications can be attributed to the fact that WR is based
The number of WR applications and their specifications have exceeded the original
assumptions of the project.
This proliferation can be attributed to the fact that WR is based
on standards, it is openly as well as commercially available, and it has a very
active community. Open nature of the project allows WR users to contribute with their
specific expertise and new developments opening the WR to even more applications.
active community. Open nature of WR allows its users to contribute to the
project with their
specific expertise and new developments, opening WR to more applications.
WR has become a \textit{de facto} for synchronization in scientific installations.
and it is now becoming industry standard within the IEEE1588.
WR has become a \textit{de facto} for synchronization in scientific installations
and it is now becoming an industry standard within the IEEE1588.
With its wide adaptation in science, commercial support, up-coming
standardization and EU-founded project to catalyze applications in the
industry, we can conclude that WR applications will continue to proliferate in
industry, WR applications will ontinue to proliferate in
science and should soon find its way into industry.
% \\
......
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