Skip to content

W
White Rabbit
Commit 3e77f47d authored by Maciej Lipinski's avatar Maciej Lipinski
Browse files
Options

Implemented simple comments from the review

parent 3ac04318
Show whitespace changes
Inline Side-by-side
Showing with 25 additions and 23 deletions
papers/ISPCS2018/wrApplicationsOverview.tex
View file @ 3e77f47d
......@@ -91,7 +91,7 @@ Precision Time Protocol (PTP, IEEE 1588) to synchronize
them. A WR network consists of switches and nodes
that implement WR enhancements:
\begin{enumerate}
\item \textbf{Synchronization with sub-ns accuracy and picoseconds precision} between all
\item \textbf{Synchronization with sub-ns accuracy and picoseconds precision} \textcolor{red}{among} all
WR switches/nodes. Such synchronization is provided by the WR extension to PTP (WR-PTP,
\cite{biblio:WRPTP}) and its supporting hardware \cite{biblio:ISPCS2011}\cite{biblio:TomekMSc}\cite{biblio:WRproject}.
\item \textbf{Deterministic and low-latency communication} between WR nodes provided by
......@@ -112,7 +112,7 @@ manner ensuring at most a single failure per year for a network of 2000 WR nodes
Since its conception in 2008, the number of WR applications has grown beyond
any expectations. The WR Users \cite{biblio:WRusers} website attempts to keep
track of WR applications. Apart from the suitable synchronization performance, the reasons for such a proliferation of WR applications
are the open nature of the WR project, the fact that the WR technology is based
are the open nature of the WR project \textcolor{red}{and} the fact that the WR technology is based
on standards. The former encourages collaboration,
reuse of work and adaptations that also prevent vendor lock-in. The latter allows using
off-the-shelf solutions with WR networks and catalyzes
......@@ -221,7 +221,7 @@ WR network elements, nodes and switches, are openly available on the Open Hardwa
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
as an open-source IP core \cite{biblio:wr-node} that can be easily used in one of
as an open-source \textcolor{red}{intellectual property (IP)} core \cite{biblio:wr-node} that can be easily used in one of
the supported boards or integrated into a custom design. WR-compatible boards
are available on OHWR in various form factors, including:
% Peripheral Component Interconnect Express (PCIe) \cite{biblio:spec},
......@@ -347,7 +347,7 @@ UTC(INRIM) over
within their campus UTC(NIST) and UTC(OP), respectively. All
laboratories are studying WR with different types and lengths of fiber links and attempt to
increase its performance, see Table~\ref{tab:timelabs}.
These studies have shown that the stability (at tau=1s) of the off-the-shelf
These studies have shown that the stability (at \textcolor{red}{$\tau=1s$}) of the off-the-shelf
WR switch is 1e-11 (Alan Deviation, ADEV, similar to a typical frequency counter e.g. Keysight 53230A)
and can be improved to 1e-12 without any modifications to the WR-PTP Protocol, see
Section~\ref{sec:JitterAndStability} and
......@@ -469,7 +469,7 @@ 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 these timestamps over WR network to a standard PC for
to timestamp input signals and send these timestamps over \textcolor{red}{a} WR network to a standard PC for
analysis proves to be an extermely convenient solution to many otherwise
challenging distributed measurements.
......@@ -489,8 +489,9 @@ challenging distributed measurements.
The most demanding WR applications in terms of timestamping are cosmic ray and
neutrino detectors that record the time of arrival of particles in individual
detector units distributed over up to kilometers. Based on the difference
in the time of arrival, the trajectory of particles are calculated. For these
detector units distributed over \textcolor{red}{distances up to several} kilometers.
Based on the difference
in the \textcolor{red}{times of arrival of the same particles detected by different unit}, the trajectories of these 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}.
......@@ -508,7 +509,7 @@ Other applications of WR that use timestamping include the
Cubic Kilometre Neutrino Telescope (KM3NeT)
\cite{biblio:KM3NeT}\cite{biblio:WR-KM3NeT-Letter}\cite{biblio:WR-KM3NeT-presentation}
located at the bottom of the Mediterranean Sea, the
Tunka Advanced Instrument for Gammy ray and cosmic ray Astrophysics (TAIGA) project in Siberia
Tunka Advanced Instrument for \textcolor{red}{Gamma} ray and cosmic ray Astrophysics (TAIGA) project in Siberia
\cite{biblio:TAIGA-WR-1}\cite{biblio:TAIGA-WR-2}\cite{biblio:TAIGA-WR-harsh-env},
Cherenkov Telescope Array to be built in Chile and Spain \cite{biblio:CTA-WR-timestamps},
the Extreme Light Infrastructures in Hungary \cite{biblio:ELI-ALP-WR} and Czech Republic
......@@ -548,7 +549,7 @@ a precise delay with respect to the input signal.
The input trigger can be either a pulse or an analogue signal exceeding a treshold.
Once the trigger occurs, the information about the trigger (e.g. ID), along with
the timestamp, is sent over the WR network to other WR nodes, usually as a broadcast.
The deterministic characteristics of the WR network allows to calculate the
The deterministic characteristics of the WR network allows \textcolor{red}{the calculation of} the
upper-bound latency for the message to reach all the WR nodes.
In order to make sure that all the "interested" nodes act upon the trigger
simultaneously, the delay between the input trigger and the time of execution
......@@ -559,18 +560,18 @@ is set to be greater than the upper-bound latency.
The trigger distribution schema has been used at CERN since 2015 in the
WR Trigger Distribution (WRTD) system for instability
diagnostics of the LHC \cite{biblio:WR-LIST}\cite{biblio:WR-LIST-2}.
In the WRTD, there is a number of instruments capable of detecting
In the WRTD, there \textcolor{red}{are} a number of instruments capable of detecting
LHC instabilities and continuously acquiring data in circular buffers. Upon detection of instabilities, such a device generates a
pulse that is timestamped by a Time-to-Digital Converter (TDC) integrated in
a WR Node \cite{biblio:fmc-tdc-5cha}, as depicted in Figure~\ref{fig:WRTD}.
The timestamp produced by the TDC is broadcast over the WR network,
with a user-assigned identifier, allowing to uniquely identify the source of the
with a user-assigned identifier, allowing \textcolor{red}{the unique identification of} the source of the
trigger. WR nodes interested in this trigger take its timestamp, add
a fixed latency (300$\mu s$) and produce a pulse at the calculated moment. This
pulse is an input to a device that continuously acquires beam monitoring
data in a circular buffer. These buffers are deep enough to accommodate the introduced
fixed latency so that they can be rolled back to provide diagnostic data of the
beam at the time the instability was detected by the source device. In such way,
beam at the time the instability was detected by the source device. In such a way,
the onset of instabilities can be coherently recreated. It is worth noting
that the diagnostic instruments used in WRTD do not implement WR. They are integrated with
WR through timestamping of their trigger outputs and generation of inputs that trigger
......@@ -584,7 +585,7 @@ their actions.
\end{figure}
The concept that has proven to work in WRTD is now being generalized to
The concept that has \textcolor{red}{been} proven to work in WRTD is now being generalized to
provide trigger distribution for CERN's Open Analog Signals Information System
(OASIS) \cite{biblio:OASIS}. OASIS is a gigantic distributed oscilloscope that
provides $\approx$6000 input channels and spans all CERN's accelerators except LHC.
......@@ -672,8 +673,9 @@ the CERN accelerators, except LHC, should be running WR-BTrain operationally \ci
\section{Radio-Frequency Transfer (RF)}
\label{sec:RFoverWR}
% \subsection{Basic Concept}
Radio-frequency transfer allows to digitize periodic input signals in a WR master node, send
their digital form over a WR network, and then regenerate this signal coherently with a fixed delay in many
Radio-frequency transfer allows \textcolor{red}{the digitization of} periodic input signals in a WR master node,
\textcolor{red}{the sending}
their digital form over a WR network, and \textcolor{red}{the subsequent regeneration of the} signal coherently with a fixed delay in many
WR slave nodes. In such schema, depicted in Figure~\ref{fig:RFoverWR} and detailed in \cite{biblio:WR-LIST},
\begin{figure}[!ht]
\centering
......@@ -1136,11 +1138,11 @@ have shown that the performance of a WR switch currently commercially available
improved:
\begin{itemize}
\item ADEV clock stability (tau=1s) from 1e-11 to 1e-12,
\item Random jitter from 11 to 1.1~ps RMS
\item Random jitter from \textcolor{red}{1.1 to 11~ps} RMS
over 1Hz-100kHz.
\end{itemize}
This prompted the development of the Low-Jitter Daughterboard
\cite{biblio:WR-LJD} that improves the performance of the WR switch to 1e-12 without any
\cite{biblio:WR-LJD}\textcolor{red}{, which} improves the performance of the WR switch to 1e-12 without any
modifications to the WR-PTP Protocol, see
\cite{biblio:MIKES-50km}\cite{biblio:SYRTE-LNE-500km}\cite{biblio:WR-ultimate-limits}.
The improved WR Switches are now commercially available \cite{biblio:WR-LJD-switch}.
......@@ -1157,13 +1159,13 @@ of WR nodes and switches degrades synchronization performance, still
maintaining sub-ns accuracy.
This degradation and its sources have been carefully characterized
\cite{biblio:LHAASO-WR-temp} showing that its major contributor is the variation of hardware
delays, considering links below 10~km (see next section).
delays, \textcolor{red}{considering links whose lengths are less than 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. 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
experiment \cite{biblio:wr-cngs}\textcolor{red}{,} which requires 500ps RMS
synchronization of 7000 WR nodes in \textcolor{red}{a} harsh environmental. For temperatures between
-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}.
......@@ -1175,7 +1177,7 @@ peak-to-peak variation from 700~ps to $<$150~ps with a standard deviation $<$50~
\label{sec:LongLinks}
Experiments have shown that WR can successfully provide sub-ns accuracy on bidirectional links up to 80~km
\cite{biblio:WR-INRIM}\cite{biblio:WR-INRIM}\cite{biblio:SYRTE-LNE-25km}\cite{biblio:MIKES-50km}\cite{biblio:SKA-80km}
\cite{biblio:WR-INRIM}\cite{biblio:WR-INRIM}\cite{biblio:SYRTE-LNE-25km}\cite{biblio:MIKES-50km}\cite{biblio:SKA-80km}\textcolor{red}{,}
taking care for the effects described in the next section.
Links longer than 80~km require active amplifiers and/or unidirectional fibers.
This deteriorates accuracy due to an unknown asymmetry.
......@@ -1232,7 +1234,7 @@ synchronized WR devices are calibrated against the same "golden calibrator".
% Relative calibration is performed for a complete WR device (e.g. a given version of WR switch and SFPs)
% and needs to be repeated each time a composing elements changes.
An ongoing work on absolute calibration \cite{biblio:WR-calibration} allows
to measure precisely actual value of hardware delays and their different contributors.
\textcolor{red}{the precise measurement of the} actual value of hardware delays and their different contributors.
With such calibration, a "golden calibrator" will not be required and adding a new type of component
(e.g. SFP) to a WR network will not necessitate a time-consuming calibration of all
devices with this component.
......@@ -1241,7 +1243,7 @@ devices with this component.
\label{sec:WRin1588}
The P1588 Working Group \cite{biblio:P1588} is revising the
IEEE1588 standard, due to finish in 2019. This group has been studying
IEEE1588 standard, due to \textcolor{red}{be finished} in 2019. This group has been studying
WR in order to incorporate its generalized
version into the standard \cite{P1588-HA-enhancements}.
This resulted in a third Default PTP Profile, High Accuracy,
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment