In 5G networks, the Internet of Things, and other applications, the requirement for precise timing is getting higher and higher. In order to provide faster and more stable services, IEEE 1588 (also known as the Precision Timing Protocol or PTP) has become the most important standard for compliance. This article will show you the specifications and applications of IEEE 1588, as well as the IEEE 1588 solution introduced by Silicon Labs.
Emerging applications impose increasingly stringent requirements on timing
Precise timing is increasingly used in a wide range of applications and commercial infrastructure such as mobile communications, networking, the smart grid, the Internet of Things (IoT), industrial automation, and financial technologies (Fintech). There is an ever-expanding set of critical infrastructure that is required to provide precise times and frequencies for such applications. This requirement is growing and becoming increasingly pervasive in worldwide communication networks and commercial infrastructure.
In addition, measurement and automation systems require event synchronization and data correlation especially when multiple devices are involved in the measurement. Such devices have direct access to timing signals from a common source, or the devices must have a way to interact and synchronize their individual clocks in order to share a common time base.
Time synchronization between different devices
Devices that are close to each other and sharing a common timing signal may be the easiest way of achieving time synchronization. For example, servers or adapter cards could share a common clock signal from a backplane, enabling event synchronization to a high degree of accuracy. To accurately use such a common timing signal, some calibrations would be required to compensate for issues such as propagation delays, but since these are statically determinable, engineering such a method is relatively easy.
In some respects, GNSS-based timing (Global Navigation Satellite System) is a similar method for obtaining clock time from a common source (GNSS signal). However, having a common timing signal becomes unfeasible when the distance between devices increases, or when devices are located indoors (where GNSS signals do not penetrate) or when such devices are nomadic, frequently changing their location.
In such situations, clock synchronization needs to be distributed using either a dedicated network or an existing network. Examples of distributed clock synchronization include a PC’s internal clock synchronized to an NTP time server, or a group of devices similarly synchronized using the IEEE 1588 (PTP) protocol from a PTP Grand Master. In both these protocols, these devices periodically exchange information and adjust their local timing sources to match each other.
Both these methods of time synchronization require a continuous process of clock adjustment. If two clocks were set fully aligned and their frequency sources ran at the exact same rate, they would remain synchronized indefinitely. In practice, however, clocks are set with limited precision, and their frequency sources run at slightly different rates, and the rate of a frequency source varies over time, temperature, and some other physical factors. Most modern electronic clocks use some form of a crystal oscillator as a frequency source. The inherent instability in all oscillators requires that the clocks must continually be synchronized to match each other in frequency and phase.
IEEE 1588 meets a variety of application requirements through profiles
IEEE 1588 outlines a standard protocol for synchronizing clocks connected via a network, such as Ethernet. Released as a standard in 2002, IEEE 1588 was designed to provide fault tolerant synchronization among heterogeneous networked clocks requiring little network bandwidth overhead, processing power, and administrative setup. IEEE 1588 provides this by defining a protocol known as the precision time protocol, or PTP. The standard has undergone major improvements and has been used to cater to a multitude of applications by adding special features for such applications to evolve the basic IEEE 1588 into multiple‘profiles’.
The PTP protocol provides a fault tolerant method of synchronizing all participating clocks of varying capabilities to use the highest quality clock in the network. IEEE 1588 defines a standard set of clock characteristics. By running a distributed algorithm, called the Best Master Clock algorithm (BMC), each clock in the network identifies the highest quality clock and the self-adjusting network can run in the most optimal mode, using the best source of clock. This way, IEEE 1588 creates a simple self-adjusting network of clocks that always stays optimally synchronized.
This precise synchronization function of IEEE 1588 can be widely used in mobile and telecommunications infrastructure, data centers, smart power and power infrastructure, cyber-physical systems/industrial Internet of Things, testing and measurement, factory automation, robotic control, financial networks, and other fields.
High-stability timing source is used to reduce drift
Many factors affect the accuracy of the synchronization levels achievable using IEEE 1588. During the time between synchronization packets, the individual clocks in a system will drift apart from each other due to frequency changes in their local timing source. Obviously, this drift can be reduced by using higher stability timing sources and by shortening the intervals between synchronization packets.
In increasing order of stability – Temperature-controlled crystal oscillators (TCXOs), oven-controlled crystal oscillators (OCXOs) or atomic clocks provide higher stability than commercial standard crystal oscillators. In addition to this, a clock’s resolution and a good implementation of the timestamps transmitted in the PTP synchronization messages are important factors. Devices that have a higher resolution clock are able to more accurately timestamp messages. Significant contributors to problems are variations in network delay caused by packet delay variations introduced by variable traffic and intermediate networking devices such as hubs and switches all combine to reduce the achievable synchronization level.
IEEE 1588 complete solution accelerates system integration
Silicon Labs has introduced a new complete solution designed to simplify implementation of IEEE 1588. Silicon Labs’ ClockBuilder ProTM software, an industry-leading, highly versatile software tool, enables designers to accelerate development of IEEE 1588 system integration by combining PTP profile selection, PTP network configuration, and physical-layer clock/port configuration in a single, unified software utility.
The adoption of IEEE 1588 packet-based time synchronization is proliferating beyond communication networks into an increasingly broad range of emerging applications where system designers may have limited prior experience with timing and synchronization. One key design challenge facing engineers is optimizing IEEE 1588 system-level performance, a function of board-level hardware/software design, as well as network impairments, such as the packet delay variation caused by changing traffic loads.
Silicon Labs’ ClockBuilder Pro provides a robust, reliable solution by combining PTP profile selection, clock/port programming, and simple control of Silicon Labs’ AccuTimeTM IEEE 1588 software to configure operation for a wide variety of network conditions and topologies. Silicon Labs IEEE 1588 modules are standards-compliant with telecom (G.8265.1, G.8275.1, and G.8275.2), power (IEEE C37.238-2011 and 2017), broadcast video (SMPTE 2059.2), and default profiles, while meeting the stringent timing and synchronization requirements outlined in ITU-T G.8261, G.8273.2 (T-BC, T-TSC), G.8273.4 (T-BC-P and T-TSC-P), G.8262, G.812, G.813 and Telcordia GR-1244-CORE/GR-253-CORE.
Conclusion
Precise timing synchronization can be realized through IEEE 1588. IEEE 1588 solutions offered by Silicon Labs can help the industry accelerate the implementation of IEEE 1588. With the support of ClockBuilder Pro software and an IEEE 1588 module, it can help customers shorten the time to market and overcome the system design challenges brought by the solutions with a lower integration level, and will be the best choice for the clock synchronization function of related applications.