1588 PTP Networks: Tutorial

Applications such as process control, power distribution, motion control, and machine guidance all need distributed real-time regulation. The potentially exponential increase in use cases as a result of the developing Industrial Internet of Things (IIoT) is driving the move from legacy and proprietary networking solutions to ethernet as a unified communications medium. As a result, it is essential to provide methods to allow ethernet to give the highest levels of performance for time-sensitive applications.

The IEEE 802.1 working group continues to develop and improve standards to deliver on three aspects of Time-Sensitive Networking (TSN): accurate synchronisation, deterministic latency and controlled bandwidth. Accurate synchronisation is one of the key factors in a network implementation. The success of real-time data recording, precise sequencing of events, or even the viability of other TSN methods such as time-aware traffic scheduling (802.1Qbv) cannot be separated from accurate synchronisation.gPTP, developed from PTP, the solutions to achieving high-accuracy time synchronisation for industrial applications.

Similar to PTP, it does not require GPS installations. Such installations can be costly and are sensitive to their installation location. Additionally, gPTP uses a logical syntonization technique that can deliver fast and accurate frequency locking using ‘off-the-shelf’ components – which is an essential enabler for developing and deploying large-scale IoT systems.

So how do you prove timing and synchronisation performance meets standards compliance? Ideally a robust testing structure to validate the ‘system’ prior to deployment helps avoid adverse impact and costs associated with problems discovered post-deployment. For example, interoperability is one of the biggest challenges in deploying gPTP networks as the network requires compatible applications of the PTP profile across all devices. Testing can reduce interoperability risks by highlighting device and network misconfigurations and protocol-related issues and verify compliance to the specified standards.

Test equipment that can simulate negative network conditions such as protocol errors and timing offsets etc., allows designers to evaluate how each device within the network might respond under such conditions. This not only helps with the optimization of time-sensitive traffic flows, but also validates network performance.

Of course, test equipment should have a measurement accuracy of at least an order of magnitude greater than the specified requirements. Test equipment that provides a real-time test environment to analyse device delay calculations, path delay calculations, neighbour rate ratio calculations simultaneously, together with any stress-testing stimuli, will give you the confidence that time synchronisation performance truly does comply with the standards.

How can Calnex help?

No matter whether you want to validate PTP fields for interoperability, optimise network design, test devices in negative conditions, or even recreate real-world conditions in your lab, Calnex Paragon family and Sentinel can help. Our equipment is designed to: help address the test challenges, reduce the complexity of testing, enhance test effectiveness and validate standards compliance of devices and networks to the highest levels of accuracy available.