Ethernet Time Transfer through a U.S. Commercial Optical Telecommunications Network, Part 2
Marc A. Weiss, Lee Cosart, James Hanssen
There is a need to back up critical timing infrastructure at the national level. This paper provides an update on a joint project employing commercial equipment to send national timing signals through a telecommunication network. This experiment connects UTC(NIST) in Boulder, Colorado with UTC(USNO) at the Alternate Master Clock at Schriever AFB via a telecommunication provider's optical network. Timing signals using the Precise Time Protocol (PTP) were sent in the usual two-way fashion, but each one-way delay was measured, because we had UTC at both ends within 10 ns of each other. This part of the experiment is now nearly completed. It was started in April 2014 and extensions of the project will run through the end of 2016. It appears that there is at least one commercial transport mechanism that could serve to back up GPS for time transfer at the 100 ns level. We found that the asymmetry of the PTP time transfer resulted in 10s of microseconds of time transfer error, but that the stability as long as the connection remained was under 100 ns. The implication is that if the time transfer of a circuit could once be calibrated, it could maintain under 100 ns accuracy as long as it did not go down. We have established the likely causes of the bias, as well as run simulations of various configurations in a lab. Hence we have some certainty that similar results will apply if this technique were used as a service across the country. The focus here is using a US commercial telecom carrier to transfer time between two national real-time standards of UTC. While many researchers have shown that fiber can transfer time and frequency with high accuracy, this experiment addresses the practicality of using the US telecom infrastructure for timing.
Proceedings of Precise Time And Time Interval (PTTI)
September 28-30, 2015
Precise Time Protocol, Time backup, critical infrastructure, time transfer through telecom, Ethernet, SONET, OTN