Time Over Fiber

Executive Order 13905 ("Strengthening National Resilience Through Responsible Use of Positioning, Navigation, and Timing Services) directed NIST to make available a source of precise Coordinated Universal Time (UTC) with no dependence on Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS). In response, NIST launched a Special Test remote calibration service called Time over Fiber, which seeks to offer direct connectivity to UTC(NIST) atomic time signals at either Boulder and Gaithersburg campuses to private industry and other agencies.

Common to all forms of time transfer is the challenge of measuring, modeling, or otherwise discounting the signal delay, and variations in signal delay, between clocks. This is especially true for time transfer over fiber optic links; the best practices for delay estimation, and the expected residual noises and biases, depend critically on the nature of physical connection medium, any signal routing or interconnection nodes, and the endpoint transceiver hardware. For example, laboratory demonstrations of White Rabbit (now incorporated into the IEEE 1588-2019 High Accuracy profile) links exhibit picosecond-level transfer stability; in contrast, packet-based publicly routed schemes (like Network Time Protocol over the Internet) can suffer noise and biases of the order of many milliseconds. Interested Special Test customers are invited to contact NIST for further details.