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.
Calibration based on time (i.e. SI: International System of Units)
Absolute calibrated WR devices can serve as "Golden Standards" for the
relative calibration procedures.
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
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
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
such that the system can automatically reach absolute calibration during
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.