Time synchronisation is paramount in the Internet of Things (IoT). In industrial IoT for example, accurate synchronisation can prevent production errors by ensuring that sensors and machines work together.
In security applications such as the supervision of critical infrastructures, time synchronisation allows for precise correlation of events recorded by different devices (time clocking terminals, security cameras), centralised in a master server.
Why is a reliable and accurate time synchronisation necessary for the IoT?
The importance of time synchronisation for the IoT is based on 4 major requirements:
- Time accuracy. An accurate synchronisation ensures that actions and measurements of IoT devices are reliable.
- Security. Several types of attacks on systems and networks can be avoided by using a reliable time synchronisation mechanism. For example, in the case of replay attacks, a timestamping mechanism enables to check the integrity of messages. Timestamping represents a very efficient countermeasure against attacks.
- Interoperability. We can often find a host of different connected devices within the same network. An accurate time synchronisation is then paramount so that all devices work together efficiently.
- Energy. Connected devices must synchronise precisely while conserving their batteries. There is an interest to find energy-efficient solutions, such as time servers with low consumption for time synchronisation.
What are the different time synchronisation protocols for the IoT?
There are several technical solutions for managing the clocks of connected devices. Some of them are based on best-known protocols (NTP, NTS and PTP) while others have been specifically developed for mobile devices (IoT and mobile communication).
Below are the most widely used protocols in the IoT:
- Network Time Protocol (NTP). NTP is the best-known synchronisation protocol. It allows synchronisation of computer clocks on a network with an accuracy of a few milliseconds, while maintaining a high level of security due to the use of the NTS (Network Time Security) protocol. For many IoT applications, this level of accuracy is enough. However, in environments where a higher level of accuracy is required, in the financial or energy sector for example, NTP is not a suitable solution.
- Roughtime protocol. The Roughtime protocol is a secure time synchronisation protocol similar to NTS and offering a simple and robust solution in a decentralised installation. This protocol is particularly suitable for connected objects since it uses modern cryptographic techniques withstanding malicious attacks.
- Precision Time Protocol (PTP). PTP, or IEEE 1588 offers a solution to the need of increased accuracy that NTP does not meet. Designed to meet the needs of industrial networks where a synchronisation with a precision of microseconds is required, the PTP protocol has become an essential solution for critical applications. It is now also used for synchronising telecommunication networks, especially in the rollout of 5G, for managing reliable communications with low latency in the network. A simplified version has been introduced: the SPTP protocol (Simple Precision Time Protocol). The latter enables the number of exchanges between a server and a client to be significantly reduced, thus favouring a much more efficient network communication.
- Short Packet Transmission (SPT). In IoT networks, the bandwidth is often limited and devices must be energy efficient. Using short messages allows for efficient synchronisation without imposing an excessive network load. The small size of packets reduce the variability of the transmission delay, thus enabling devices to maintain synchronisation with a minimum margin of error.
How to maintain time accuracy?
To avoid having to synchronise too frequently with an external time server, it is recommended to equip the network infrastructure with a local time server. Indeed, these servers are capable of maintaining a good time accuracy, especially when their hardware has a built-in TCXO oscillator (Temperature Controlled Crystal Oscillator), for example.
Time synchronisation for the IoT shares some of the same requirements and solutions that can be found in clock management of a more traditional network. NTP and PTP protocols are therefore used in this context of Internet of Things. Additional issues such as interoperability between heterogeneous devices, and energy management are emerging. In order to meet this two new requirements, solutions are already being implemented (Roughtime, SPT, internal synchronisation, and so on). Besides, R&D is very dynamic in addressing these issues.
With more than 150 years of expertise in time management and present in more than 140 countries, Bodet Time is a major French leader in time synchronisation and time frequency. Eco-designed and featuring a TCXO oscillator, our Netsilon time servers provide a reliable, accurate and secure reference time.