A special calibration test under service ID # 78110S will be implemented as a link between the NIST time scale located at NIST in Boulder Colorado and a customer’s outside user facility, providing a time reference to an outside user that is directly traceable to UTC(NIST). The initial goal will be to realize an accuracy of 1 microsecond in a remote location, with the eventual improvement to 100 ns or better. The link will include a fiber connection between the endpoints and compatible end-point hardware chosen to support the required accuracy of the time signal at the user’s facility. The accuracy will be validated by diagnostics that are part of the link hardware and may also be confirmed with a portable clock trip between the end points or by similar techniques.

1. In an initial realization, the time signal at a user’s facility will be within 1 microsecond of UTC(NIST), with an ultimate goal of an accuracy of 100 ns at a user’s facility with respect to UTC(NIST).
2. In normal operation, service to a user’s facility will be implemented by a physical or logical circuit based on an optical fiber link from the NIST facility at Boulder, Colorado. It will not depend on signals from GPS satellites or any other satellite system.
3. Details of the message exchange, characteristics of the fiber link, and end-point hardware will be chosen to support the accuracy requirement specified above. A preliminary design suggests that the IEEE 1588/Precise Time Protocol may be able to satisfy the technical requirements, but this may be revised based on further study. We expect that commercial off-the-shelf hardware will be used throughout.
4. NIST will provide end-point hardware at the NIST Boulder end of the link and a customer will provide end-point hardware at the user’s end. 
5. NIST will provide an interface between the end-point hardware in Boulder and the NIST Time Scale. We expect that 5 or 10 MHz and 1 pps will be needed. An additional link to provide the time of day will also be required. These capabilities are already present in the Boulder facility or will be implemented as part of this project.
6. NIST will provide assistance in interfacing a fiber link from the demarc point of the NIST campus to the NIST Time Scale.
7. The accuracy of the time reference at a user facility will be validated by periodic calibration campaigns. These campaigns will be realized by portable clock trips, portable GPS receiver trips or similar methods. The calibration hardware will be transported to a user facility and then returned to NIST; no calibration hardware will be permanently installed at a user facility other than whatever is present as part of the end-point interface described above. These campaigns will be conducted as often as needed, but generally not more often than once per month.
8. A link will be designed so that a temporary loss of connectivity between the end points or a reboot of any of the components of the link system will not affect the calibration.
9. Parties to a special test will have complete control and management responsibility for the components of the system at their site. Some minimal access, TBD, to a remote site may be needed from time to time to support the calibration campaigns discussed above. No other access to either facility is expected to be needed. The fiber connection will be operated and maintained by a third-party communications provider, and employees of the third party might need access to repair the fiber link.
10. The NIST contribution to this work will be charged to the customer "at cost," with the details TBD on a case-by-case basis. 
11. The performance of a link will be monitored from Boulder and the link status will be incorporated into the real-time monitoring system. The monitoring system can provide various status and failure messages to the user’s staff. The hardware at the NIST Boulder site is highly redundant, but the fiber link and the interface hardware represent a single point of failure. We can choose to accept the risk of such a failure or we can discuss various mitigation strategies. The mean time between failures (MTBF) is probably quite long, but the mean time to repair (MTTR) could be appreciable.
12. The project will be re-evaluated after 6 months of operation.