In a world where automation based on robust and reliant connectivity is being implemented across a wide range of industries, time synchronization within networks has become a key factor in advancing technology and developing new applications to benefit humanity.
This year IEEE has brought changes to how time within networks is synchronized with the publication of IEEE 1588™-2019 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems.
IEEE 1588 is commonly known by the protocol that it specifies, the Precision Time Protocol (PTP), which is used to transfer time through a network. A single endpoint in the network acts as the source of time, and PTP transfers that time through various switches and routers to other endpoints so that everything in the network operates in a synchronized manner.
Why is PTP needed?
Consider the implementation of a clock in a device.
The device’s clock hardware consists of an oscillator that is specified as ticks per second, such as 100 million ticks per second (100 MHz). Software in the device reads a counter that tells it how many ticks have occurred since the oscillator was powered on. If the device has a network connection, it can receive time from another device over the network. If the devices need to synchronize time accurately, simple messages that contain the current time are insufficient because time changes as messages travel over networks. Slight operational discrepancies between oscillators can also cause times to eventually drift apart, and that drift can also be affected by environmental factors like temperature. The PTP protocol operates continuously to resolve these challenges.
IEEE 1588-2019 brings real-world benefits to academia and research institutions, world’s financial markets, the automotive and industrial automation sector, the telecom and broadcast industry, power generation and distribution companies. The standard has the potential to be further augmented and utilized to drive new and improved applications across a number of domains.
CERN and White Rabbit
The European Organization for Nuclear Research (CERN) and its well-known Large Hadron Collider (LHC) uses a large Ethernet network where the required time synchronization performance is sub-nanosecond.
To meet these requirements a PTP Profile called White Rabbit was developed that specified many innovative techniques, such as enhancements for use of Ethernet hardware clocks, and calibration of asymmetry in fiber optic cabling. A PTP profile is a configuration of PTP for a specific application. The specifications from White Rabbit are incorporated into IEEE 1588-2019 as the High-Accuracy Delay Request-Response Default PTP Profile. In effect, formalizing White Rabbit as part of the IEEE 1588 standard helps to bring best-in-class performance to any application.
Telecom Internet Service
While devices are connected to the Internet using an Ethernet cable, telecom service providers also implement large Ethernet networks outside of the home or office, and similar Ethernet networks exist within 4G/5G base stations to transfer mobile phone data to and from the Internet—all of which requires time synchronization based on PTP.
Past ITU-T standards specified storage of performance statistics in logs, with local measurement in 15-minute and 24-hour periods, accessible at any time by a remote management client. While ITU-T’s past logging standards were unrelated to PTP, experts from ITU-T helped to specify this sort of logging for PTP during development of IEEE 1588-2019 resulting in the Performance Monitoring feature published within IEEE 1588-2019.
In-Vehicle Automotive and Industrial Automation
IEEE 802 is a family of standards for local area networks, such as Ethernet (IEEE 802.3) and Wi-Fi (IEEE 802.11) technologies. As part of that family, the IEEE 802.1 Working Group specifies a PTP Profile within IEEE 802.1AS – Timing and Synchronization for Time-Sensitive Applications. The PTP Profile in IEEE 802.1AS is well known for providing a cost and performance tradeoff that is an excellent fit for time-sensitive applications, such as the network inside a self-driving car and the network on a factory’s production floor.
For a self-driving car, devices read input data from the physical world (e.g., radar and cameras to detect objects in front of a car), perform computations on that data, and generate output back to the physical world (e.g., steer the car). These in-vehicle devices communicate over a network, and the devices must be synchronized in time, which is where IEEE 802.1AS comes in.
The factory automation example is similar. Robots on the factory floor read input data (e.g. “Is there a bottle in front of me?”), perform computations, and generate output data (e.g., fill the bottle with the factory’s sparkling water). The devices on the factory floor are networked and time synchronized, and IEEE 802.1AS fulfills their requirements.
Historically, television studios used direct audio/video cabling, but over time many studios have transitioned to use Ethernet networking. In the context of Ethernet, the audio often travels in separate messages than the video. As one would expect, time synchronization is important for these studio networks to precisely control their audio and video. The Society of Motion Picture and Television Engineers (SMPTE) specifies a PTP Profile for this application (ST 2059-2:2015).
Organizations like SMPTE need the ability to configure PTP in a switch using broad-based protocols like SNMP and NETCONF. As a result, the new revision IEEE 1588-2019 contains architectural changes that significantly clarify and improve the ability to configure PTP using other standards. Using IEEE 1588-2019 as a foundation, work is ongoing in SMPTE and other PTP Profile organizations to establish a clear roadmap for PTP configuration into the future.
Power companies often use Ethernet networks for operating and managing electrical equipment. To quickly detect and mitigate electrical faults, companies use synchrophasor technology, meaning a precise measurement of the magnitude and phase angle of the sine waves found in electricity. It is important to obtain multiple synchrophasor measurements in different neighborhoods, and those measurements must be accurately synchronized in time. To achieve this the electrical power industry specifies several PTP Profiles for synchronization, one of which is the IEEE C37.238 standard .
Due to accuracy requirements, the IEEE C37.238-2011 revision specified the addition of Time Inaccuracy information. So, as PTP transfers time through the network, each Ethernet switch adds its own inaccuracy to this C37.238-specific information.
As development proceeded on the new IEEE 1588-2019 revision, other applications saw value in the work done in IEEE C37.238 on Time Inaccuracy. As a result, IEEE 1588-2019 specifies an analogous and slightly enhanced feature called Enhanced Synchronization Accuracy Metrics.
Today, financial trades are often made by automated systems. Financial trading companies build out large networks that span multiple cities, and due to government regulations and other reasons, the trading actions in each city must be accurately time synchronized.
IEEE 1588-2019 specifies enhancements and clarifications for mixing multicast and unicast communication in a single PTP network. These multicast/unicast clarifications are being used for future development of a PTP Profile specifically for financial applications.
IEEE 1588 has become a pervasive part of networking in modern times. The standard’s concept of a PTP Profile enables each application to customize the protocol to its needs. As the foundation of that PTP Profile ecosystem, the new IEEE 1588-2019 revision has been modified and enhanced to incorporate new technologies, bringing measurable benefits to our increasingly connected world.