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The concept of Zero Trust Network first appeared in 2010 and introduces a new way of thinking the security of computer networks. It is opposed to the classical vision which consists in maintaining hackers outside the network, therefore making the inside of a network a poorly secured area. With this oldest vision, once a hacker enters the network, it becomes difficult to follow and prevent this hacker from accessing to all resources.

The NTP protocol broadcasts a time information within a network in order to make sure that all clocks on a network are synchronised with an acceptable offset. NTP is one of the first protocols to be introduced and it has met a great success. NTP is easy to implement since it operates on the Internet network and since there are public servers available to retrieve the time.

The need for time synchronisation is omnipresent in industrial companies, where the accuracy of operations can have a significant impact on security, productivity and costs. Technologies such as NTP, IEEE 1588v2 (PTP) or IEEE 802.1AS are essential for synchronising systems present on the same network with each other or with reference clocks.

It is paramount to make sure that all machines on a computer network are synchronised for software or industrial operations of many economic sectors. There are several ways to time synchronise machines via the network. To do so, time synchronisation protocols are used to synchronise different machines by broadcasting timestamps. These protocols usually broadcast the time of a reference clock such as an atomic clock or a GPS. However, the more extended a network, the more difficult it can be to synchronise machines.

Nowadays, the most widely used protocols are NTP (Network Time Protocol) and PTP (Precision Time Protocol). Each one of these protocols meets specific purposes which are more or less suitable depending on required applications.

Precision Time Protocol (PTP) is a time synchronisation protocol which ensures that all clocks within the same network are synchronised with the minimum possible offset. To do so, the PTP protocol will broadcast the time of a reference clock, which is most of the time an atomic clock or a GPS.

The PTP protocol is standardised under the name IEEE-1588. The first version dates back to 2002. It has been developed to offer greater accuracy than existing protocols (such as NTP Network Time Protocol). PTP offers a theoretical accuracy in the nanosecond range on LAN networks.

The breakdown of a service within a computer network is an issue that must be avoided where possible, and resolved as quickly as possible when it could not be avoided.

When the service in question turns out to be an essential component of several other services such as time synchronisation via a time server implementing the PTP or NTP protocol, then the breakdown can have disastrous consequences. Fortunately, there are several ways to avoid such breakdowns to happen.

Whether they broadcast video (television or streaming) or audio (radio) content, time synchronisation is paramount for broadcast networks.

Indeed, if equipment is not perfectly synchronised, various errors can occur such as audio/video desynchronisation, or editing errors caused by inverted frames.

These issues can be amplified due to poor network quality or very important traffic. It is therefore important for time synchronisation to be optimum in order to offer a satisfying user experience.

Beyond a simple time display, an airport must deliver a reliable, accurate and highly secure time to all equipment present in the different airport terminals.

An exact time enables to coordinate operations across the airport network, to organise departures and arrivals, to anticipate delays, etc. A single time reference must be deployed across all devices on the IT network to achieve synchronisation (clocks, computers, check-in counters, video surveillance systems, and so on). To meet the need of high time reliability and ongoing availability of time information, airports equip their control tower and operations centre with high-precision time servers.

IRIG standards (Inter-Range Instrumentation Group) define a set of timestamp broadcast parameters for synchronising devices over a limited network. Each standard defines a frame format and a transmission method (carrier frequency, modulation, etc). Not all standards have the same resolution and are able to obtain the same accuracy.