Technical Resources
Timing and Synchronization for Modern Power Grids
Accurate and synchronized timing signals are necessary for effective monitoring,
control, coordination, and protection of power grids. This report explores the various services
prevalent in power grids, focusing on their critical timing requirements for effective operational
functionalities and performance. The importance of precise timing and synchronization across various
power grid services is examined, highlighting how timing and synchronization influences the
reliability and efficiency of power grids.
October 13, 2025
Secure NTP Implementation for Power System Synchronization
The Center for Alternative Synchronization and Timing (CAST) promotes resilient,
terrestrial based time synchronization through protocols such as Precision Time Protocols (PTP) and
Network Time Protocol (NTP) to maintain accuracy across the electric grid. This technical bulletin
focuses specifically on secure NTP implementation, covering best practices, closed-loop timing architecture,
and step-by-step configuration for both general purpose and dedicated NTP servers, as well as clients. CAST
reduces reliance on public time sources and ensures resilient, secure timekeeping across power system
operations.
August 12, 2025
Implementing a Terrestrial Timing Solution: Best Practices
This document is an overview and guide on the concept of precision time and how an
alternative terrestrial timing solution to the Global Positioning System (GPS) can be implemented. A set of
recommendations and best practices, derived from research at Oak Ridge National Laboratory, across industry,
and within the US government are provided to enable implementation of a system of precision timing and
synchronization to support resilient operations for the US grid. Precision time is a fundamental necessity
for operating the grid today, and it becomes even more important as the grid modernizes with distributed
energy resources, microgrids, and precision sensors placed throughout the grid system to ensure
failure-resistant operations. The Global Navigation Satellite System (GNSS), which includes GPS, is currently
the primary provider of precision timing. A terrestrial-based system for time delivery and synchronization to
augment GPS is outlined in this document. It provides secure time, synchronized with Coordinated Universal Time
(UTC), in the event of outages or other interruptions associated with time delivery.
July 23, 2025
Performance of Precision Time Protocol (PTP) over Optical Transport Networks (OTN)
The US Department of Energy Office of Electricity has partnered with Oak Ridge National
Laboratory (ORNL) to find alternative precision timing solutions for the nation's power grid. This effort is in
response to the vulnerabilities identified in the Global Navigation Satellite System (GNSS), of which the US Global
Positioning System (GPS) platform is a part. Additionally, Executive Order 139055 has highlighted the need for
alternative or backup timing solutions. ORNL has established a Timing Lab and has been testing various
technologies and timing devices as part of this effort. Precision Time Protocol (PTP), and the off-the-shelf
timing devices and network connections that support it, are among the alternatives being tested. This work reports
the accuracy of PTP over the Optical Transport Network (OTN) and is part of a series published by the Center for
Alternative Synchronization and Timing (CAST).
June 20, 2025
Lessons Learned from TWSTFT Implementations
Two-way satellite time and frequency transfer (TWSTFT) has been a trusted time
transfer and synchronization method for a long time. It provides good timing accuracy, usually 100 ns
or less.
May 16, 2025
CAST Holdover Experiment #1 - DOCXO and Magnetic Cesium Reference
Stable and accurate timing forms the foundation of many modern essential services.
While global Navigation Satellite Systems (GNSS) provide a cheap way to achieve extremely accurate
timing, these systems are vulnerable to interference and complete outages, forcing systems that rely
on them into a state of holdover. Testing and characterizing holdover performance is therefore
essential for ensuring that these modern services do not go down when GNSS-based timing is unavailable.
March 27, 2025
Timing Holdover Experiments Summary
Stable and accurate timing forms the foundation of many modern essential services.
While Global Navigation Satellite Systems (GNSS) provide a cheap way to achieve extremely accurate
timing, these systems are vulnerable to interference and complete outages, forcing systems that rely
on them into a state of holdover. Testing and characterizing holdover performance is therefore
essential for ensuring that these modern services do not go down when GNSS-based timing is unavailable.
March 27, 2025
NTP Monitoring
Network Time Protocol (NTP) is an established internet protocol that has been widely
used for clock synchronization between computers and time-critical devices over packet-switched networks.
It is a bidirectional protocol that allows network nodes to send timing information in a hierarchical
structure. In the US Department of Energy's national energy delivery mission, NTP has been widely
deployed for keeping the power grid devices in sync for safe and efficient electricity delivery. ORNL's
Center for Alternative Synchronization and Timing (CAST) aims to provide a terrestrial timing
infrastructure alternative for next-generation power delivery by using an effective combination of NTP
with high-precision Precision Time Protocol (PTP). In CAST, whereas PTP carries the bulk of long-distance
terrestrial synchronization transmission, both NTP and PTP can be effective means for enterprise internal
time synchronization subscriptions. This bulletin examines various tools and methods that can be used to
monitor multiple aspects of NTP operation and its performance.
September 20, 2024
Implementing NTP Internally
Network Time Protocol (NTP) is a widely consumed standard for distributing time
across network devices. It is also a legacy system with known security vulnerabilities. The
vulnerabilities can be mitigated through modern implementations of NTP that include internal and
external redundancy, ensure fault tolerance, and reduce cyber threats. While Precision Time Protocol
(PTP) is a preferred approach, this technical bulletin provides recommendations for leveraging NTP
internally when architectures require it or devices are not PTP-enabled.
August 19, 2024
The Role of GPS for Timing System Calibration
This CAST technical bulletin highlights the importance of GPS connectivity for
Remote Timing Units. This bulletin will describe how GPS is currently used in a timing and
synchronization architecture to validate the accuracy of a PTP signal. GPS provides an important
link to an authoritative timing source and enables the calibration and validation of terrestrial
timing systems for meeting power grid accuracy requirements. Absent GPS, a well-calibrated
grandmaster clock will maintain a highly stable PTP timing distribution using a reference atomic
clock, such as a Cesium reference.
June 11, 2024
The Flow of Timing Signals from Clocks to Devices
This CAST technical bulletin gives a description of the updated efforts
on Oak Ride National Lab (ORNL) Center for Alternative Synchronization and Timing (CAST)
project's work investigating a terrestrial-based high precision timing infrastructure
intended for tie synchronization of the next generation power delivery infrastructures.
We will provide a high-level description of the CAST application context, key protocols,
critical architecture issues, and how GPS/timing data traverse through the system.
May 30, 2024
Network Monitoring using PTP
This CAST technical bulletin highlights the effect of network path routing
automation on time synchronization precision, network performance visibility through synchronization data.
Utilizing Precision Time Protocol (PTP) over DOE's Energy Sciences Network (ESNet), we show that as ESNet
reroutes network traffic to maintain/improve overall network latency can result in significant inaccuracies
for time synchronization between network devices.
January 26, 2024