Time Synchronization of Devices in IP Networks

time synchronization

You probably know the Network Time Protocol (NTP). This protocol is used for time synchronization of devices in the millisecond range. But what to do if accuracies in the microsecond range are required?

The Network Time Protocol (NTP) transmits time information from the Internet and allows time synchronization of devices that are often distributed worldwide.

The Precision Time Protocol (PTP) is used for the time synchronization of devices and clock signals with an accuracy in the milliseconds to microseconds range.

Typical applications include professional multimedia broadcasting (e.g., broadcasters, IPTV solutions, voice messaging systems), cellular networks, Internet of Things solutions, autonomous vehicles and many more.

The accuracy of the timing signals of different sources depends on their implementation, the signal propagation time, the temperature of the clock source (e.g., quartz crystal), but also in other components, magnetic and electrical fields, the age of the system, and many other factors.

The delay time when exchanging time information over networks is a big challenge. Especially with networks that use the Internet Protocol for information exchange, latency of IP packets over physical links and network paths are difficult to predict because packets of different size have to be transmitted over the same links and block each other. As a result, latency increases, delay time varies and, in the worst case, results in packet losses (since packet buffers overflow or transmission errors occur on lines).

For all devices to have the same time and clock information, permanent synchronization between systems is required (both in terms of frequency and phase).

Distributed systems require a master clock and a synchronization protocol. This means that devices periodically exchange time information and constantly adjust themselves.

Known standards describing time and clock synchronization are “IEEE 1588-2008 – IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems” and “ITU-T G.8275 and Y.1369 Architecture and Requirements for Packet-based Time and Phase Distribution”

IEEE 1588

The IEEE 1588 standard describes a protocol (the “Precision Time Protocol (PTP)” for time synchronization in multicast-capable networks (e.g., Ethernet).

The goals of the specification were to define a fault-tolerant synchronization over heterogeneous networks with low protocol overhead, low bandwidth requirements, and low administration overhead.

In general, the Precision Time Protocol is used for time synchronization with a master clock. This master clock can come from different sources, e.g. from the Global Positioning System (GPS). To obtain and distribute the time information from the GPS signal, special components are available on the market.

Link:

Webinar „Precision Time Protocol“ (in German)

About the Author

Ronald Schlager is an independent trainer, consultant, book author and blogger covering topics around communications technologies and their applications. Ranked #23 in Onalytica´s List of Top 100 Influencers of “Unified Communications”.

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