These pages provide information on the calibration of White Rabbit devices. The goal of this subproject is to create methods for, what we call, absolute calibration.
Relative calibration
Calibration based on a WR "Golden Standard".
-
White Rabbit devices
calibration
- provides coarse calibration values for the official releases of WR Switch and WR PTP Core firmware. You can use them as defaults for matching hardware and gateware version. However, to achieve the best possible synchronization results you should perform the full calibration procedure for your WR hardware.
- WR Calibration Procedure
Absolute calibration
Calibration based on time (i.e. SI: International System of Units)
measurements.
Absolute calibrated WR devices can serve as "Golden Standards" for the
relative calibration procedures.
Overview
Absolute calibration enforces standardization since it enables
independent developers and/or vendors to exchange their WR gear while
achieving absolute sub ns timing. Absolute calibrated devices can be
used as "golden standards" for the relative calibration
procedure.
Absolute calibration is achieved by measuring the time relationship (Δ
TXcal, Δ RXcal) between the external electrical
phase planes of the PPS signal and the interface to the
Electrical-Optical / Optical-Electrical converter (EO/OE, usually the
electrical SFP connector) as shown in Figure
1.
Figure 1: White Rabbit link delay model for absolute calibration
EO/OE converters have their own calibration parameters that define the
relationship between their electrical and optical phase planes.
For some WR applications the electrical system can be broken into
different parts (for example a DIO
FMC to be plugged
onto a SPEC board). When the
electrical phase plane of the PPS signal is defined on such an
exchangeable module and future exchange is foreseen then separate
calibration of each of these parts is necessary. The calibration
parameters for EO/OE converters and exchangeable modules are stored in
EEPROM
such that the system can automatically reach absolute calibration during
link initialization.
Last but not least, there is an asymmetry (WR asymmetry coefficient
alpha) between forward- and backward propagation delay over the fiber
due to chromatic dispersion. This can be measured and monitored in-situ.
A detailed description and overview of Absolute Calibration can be found
in the ISPCS 2018 Best Paper
Award winning article
below:
White Rabbit Absolute
Calibration
published in: 2018 IEEE International Symposium on Precision Clock
Synchronization for Measurement, Control, and Communication
(ISPCS)
To conclude:
Calibration of WR devices spans three main calibration topics, each described on the following wiki pages:
- Electrical absolute calibration
- Electrical-Optical / Optical-Electrical
- Insitu determination of alpha
Contacts
Peter Jansweijer, Henk Peek, Tjeerd Pinkert, Guido Visser
Status
Date | Event |
---|---|
24-02-2016 | Start of project |
22-07-2016 | added description of White Rabbit Absolute Calibration Procedure |
17-07-2017 | divided calibration into three topics each described in sub-wiki pages |
26-05-2018 | change the somewhat confusing titles at the top of the page |
28-05-2018 | fine tuned relative v.s. absolute definitions. |
29-11-2018 | added reference to ISPCS-218 paper. |
04-03-2019 | upadated references after OHWR migration. |
Last updated: 4 Mar 2019