What is PTP and why should you use it

But what is PTP, how does it work and why should you consider using it? In this post we will take a look at some of the issues involved in measuring time and frequency. We will look at what is involved in ensuring that time and frequency systems are accurate and in line with the latest technical and regulatory developments.

Measuring time and frequency

Many organisations use the Global Positioning System (GPS) for their timing systems. But GPS has a range of issues that can introduce significant errors in time and frequency measurements. For mission-critical systems, these errors can be disastrous unless you have a very reliable oscillator and monitor the steering of the oscillator by the GPS carefully. As a result, a variety of government agencies and industry bodies, including Netnod, recommend that organisations have a reliable secondary source of time.

Issues with GPS based solutions include:

• signal interference

• unpredictable latency

• leap seconds

• oscillator instabilities

• rollover issues

• vulnerability to attack using signal jamming and spoofing

Some of these issues are also worrisome for other mechanisms used to steer time and frequency. We will take a look at how GPS issues can affect two industries in which measuring time to the highest level of accuracy is essential: the energy sector and financial services.

Time and power

The power grid needs precision timing for monitoring and coordination. Without a consistent and accurate source of time, it is impossible to effectively monitor power systems, to identify issues and to mitigate specific events. Accurate time measurement is essential for ensuring power supply and demand are consistently matched and power outages are prevented.

The performance of Phasor Measurement Units (PMUs) provides a good example here. PMUs are used to measure voltage, current and frequency throughout multiple points on the power grid. They determine the magnitude and phase angle of current or voltage making real-time measurements throughout the power grid known as synchrophasors. The synchrophasor data provides power grid operators with real-time data enabling them to mitigate potential stresses or possible outages on the grid. But even the smallest error from the time source, or delay in propagation between time source and point of time stamping, leads to incorrect synchrophasor data and can cause serious consequences.  

Most PMUs use GPS for their Coordinated Universal Time (UTC) source. However, since GPS signals are weak and have issues such as signal interference, jamming, loss of signal, and spoofing, they cannot be relied on as the only source of time. For synchrophasors and other mission-critical applications dependent on high precision timing, a redundant, reliable and accurate secondary time source is essential.  As a result, the electric industry is currently working to integrate PTP in power grid applications and systems.

What is Precision Time Protocol (PTP)?

PTP is defined in the IEEE 1588 standard (“Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems”). It has been designed for systems needing the highest level of accuracy. By enabling hardware time-stamping, and used in conjunction with specific hardware arrangements, PTP can provide time stamping to the level of tens of nanoseconds. As PTP systems send packets both from and to the master clock, it is possible to cancel the networking delay from the master clock and avoid problems in time propagation. As a time distribution protocol offering the highest level of precision without the inherent weakness of GPS, PTP is used in military applications, the electric industry, at high-level research institutes (such as CERN), in telecommunications and in the financial services industry.

Time and money

The financial services industry is based on the precise timing of financial transactions. However, there have been instances of attacks that have jammed the GPS signals used to time-stamp financial transactions. Many financial firms have turned to alternate time sources to remove their reliance on GPS and to ensure they have traceable and certified time for their financial transactions. The Times reported in 2017 that financial firms in the City of London were so concerned about the issue that the Intercontinental Exchange signed a deal with the UK’s National Physical Laboratory (NPL) to buy a direct time feed from the NPL’s atomic clock.

Accurate time in the financial sector has become an increasingly important issue with the new EU regulations on the time stamping of financial transactions that were introduced in 2017. The  requirements for clock synchronisation, as specified in Commission Delegated Regulation (EU) 2017/574 (known as RTS-25), specifically require that financial firms establish timestamp systems with traceability to UTC and the capacity to document the system design, functioning and specifications. With annual reviews of their system’s compliance to this regulation mandatory, many financial firms are turning to sources of traceable time that provide high precision without the issues, complications and potential inaccuracies involved with GPS.  

Staying in time

For any systems where time precision is important, you should:

• get time and frequency from multiple sources

• compare them with each other

• measure frequency and phase errors

• know the stability of the oscillator you use

• make a risk assessment of errors

• compare with acceptable errors

PTP and Netnod

Netnod provide PTP services delivered over a dedicated fibre and offering a robust, reliable and highly accurate source for time and frequency.

Netnod’s redundant time and frequency node, with cesium atomic clocks
 

More information about Netnod’s PTP service is available here.

References

“Time Synchronization in the Electric Power System, NASPI Technical Report”. NASPI Time Synchronization Task Force, March 2017.  Accessed 14 May 2019.

“London’s Atomic Bombshell for Hackers.” The Times, 9 May 2017.  Accessed 14 May 2019.