Preparing to Extend Commercial Telecom PTP Across the United States

Many areas of industry have a growing need for accurate time, in addition to that provided from GPS. This paper provides an update on a joint project employing commercial equipment to send national timing signals through a telecommunication network. We are now developing a link between the UTC(NIST) time scale located in Boulder, Colorado and a GPS-based reference in a telecommunications office in Chicago, Illinois. The office is a large facility with several companies having their own Points-of-Presence. Timing signals using the Precision Time Protocol (PTP) will be sent in the usual two-way fashion, but each one-way delay will be measured, because first, we will have UTC time scales at both ends of the network that were within 20 ns of each other, and second, the device in Boulder will be acting as a probe, measuring the one-way delays. By probing the link, rather than simply slaving one device to a master, we are able to better characterize the performance of the network itself, and investigate the cause of any asymmetry. In this way, we can show the possibility of an actual service for delivering UTC directly from a national lab across the U.S. using the public telecom infrastructure. Previously, this experiment connected UTC( NIST) between Boulder, Colorado with UTC(USNO) located at Schriever Air Force Base in Colorado via a telecommunication provider's optical network. We are calling that phase 1. We found that the asymmetry of the PTP time transfer in phase 1 resulted in 10s of microseconds of time transfer error, but that the stability through the entire connection was better than 100 ns, as long as the connection remained complete. This implies that if the time delays of the network could be calibrated, it could maintain under 100 ns accuracy as long as the circuit did not go down. We are now preparing for phase 2 of this experiment, to connect UTC( NIST) to a telecom office in Chicago, using UTC from GPS as the reference there.