Minimizing the impact of asymmetry in High Accuracy White Rabbit long distance links using Single Fiber Single Wavelength transceivers

The meaning of the term high accuracy in industrial time synchronization scenarios has evolved over the years. After the incorporation of the High Accuracy (HA) profile in the IEEE 1588-2019 standard, the term high accuracy has been redefined in practice to sub-nanosecond accuracy. Applications like the coherent network Primary Reference Time Clock (cnPRTC), High Frequency Trading, Time-over-Fiber (ToF) or quantum networking keep pushing further down this meaning. Therefore, sub-nanosecond accuracy has led to focusing into usually neglected time error sources, targeting picosecond or even femtosecond error sources. In this context, calibration techniques and the characterization of optical distribution effects on the accuracy of time synchronization protocols have gained attention over the last years and remain an active topic in the community. This paper does a review of the explored mechanisms for both calibration and optical distribution characterization. This work is complemented with an initial characterization of the performance of White Rabbit (WR), as a pre-implementation of IEEE 1588 HA profile following a novel approach based on the use of Single Fiber Single Wavelength (SFSW) optics combined with Optical Time-Domain Reflectometer (OTDR) for time synchronization.