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

Last updated: 4 Mar 2019