Time Transfer Using an Asynchronous Computer Network: Results from a 500-KM Baseline Experiment

Sven-Christian Ebenhag, Kenneth Jaldehag, Per Jarlemark, Per Olof Hedekvist, Ragne Emardson, and Peter Löthberg

Abstract:	SP Technical Research Institute of Sweden and STUPI have performed a time transfer experiment over a 500-km-long baseline between Borås and Stockholm. The time transfer technique passively utilizes the data bit stream generated in an optical fiber computer network based on the packet over SONET/SDH technique. A small fraction of the optical signal is monitored both at the transmitter and at the receiver. When an occurrence of a unique bit sequence of the SDH frames is detected, an electrical pulse is generated and compared with a resolution of 100 ps to a local clock. With data from all four positions of an optical bidirectional link, two-way time transfer can be achieved and any symmetrical variations in delay can potentially be cancelled. The results presented here have been obtained over OptoSUNET, the new Swedish University Network. In the experiment, 10 Gbit/s traffic from SP over OptoSUNET is extended in Stockholm to STUPI, a clock laboratory which is the second node in this setup. This reconnection enables that a communication channel is established between two nodes, with no intermediate jump. The time-transfer experiment includes more than 500 km of fiber transmission, of which several km is via air-lines. By comparing the results from a GPS carrier-phase link, a precision better than ± 1 ns is achieved over several months of measurements between two hydrogen-masers.
Published in:	Proceedings of the 39th Annual Precise Time and Time Interval Meeting November 27 - 29, 2007 Hyatt Regency Long Beach Long Beach, California
Pages:	477 - 488
Cite this article:	Ebenhag, Sven-Christian, Jaldehag, Kenneth, Jarlemark, Per, Hedekvist, Per Olof, Emardson, Ragne, Löthberg, Peter, "Time Transfer Using an Asynchronous Computer Network: Results from a 500-KM Baseline Experiment," Proceedings of the 39th Annual Precise Time and Time Interval Meeting, Long Beach, California, November 2007, pp. 477-488.
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