The role of precision time protocol synchronisation in Ethernet cameras

21st December 2023
Kristian McCann

Ethernet cameras rely on precise timing and synchronization for accurate data transmission. The Precision Time Protocol (PTP) ensures sub-microsecond accuracy, synchronizing time clocks among IP-connected devices. 

Ethernet cameras, renowned for their efficient data transfer, integrated system functionalities, high bandwidth capabilities and a reliable connectivity, hold pivotal roles across various domains like surveillance, industrial automation, medical, and retail sectors. These cameras rely on precise timing and synchronisation to capture and transmit data accurately. This is where the Precision Time Protocol (PTP) comes into play, providing a solution for achieving synchronisation with sub-microsecond accuracy.

What is PTP?

Precision Time Protocol is an Ethernet or IP-based protocol utilised for synchronising time clocks among a group of IP connected devices. Its primary purpose is to achieve exceptionally accurate time synchronisation, often reaching sub-microsecond levels of precision. This level of precision is particularly valuable in applications where precise timing and coordination among networked devices are essential. PTP’s specifications are outlined in the IEEE 1588-2008 standards, commonly known as 1588v2.

In understanding how PTP works and achieves this precision, let’s explore its operational details.

How PTP works?

PTP operates on a master-slave architecture, which involves designating a single master device on the network as the reference clock. All other devices in the network act as slaves and synchronise their clocks to match the master’s time. This synchronisation process is facilitated through a series of messages exchanged between the master and slave devices.

The key components of the PTP synchronisation process are shown below.

Key Components of PTP Synchronization

Figure 1: Key Components of PTP Synchronisation


Key components of PTP synchronisation

Grandmaster clock: The Grandmaster Clock serves as the principal time source, often receiving highly accurate time information from sources like Global Positioning System (GPS) or atomic clocks. The Grandmaster Clock establishes the ultimate reference time for the entire PTP network.

Boundary clocks (masters): Boundary Clocks, also known as Masters, are intermediate devices within the PTP network. These clocks have multiple network ports, allowing them to act as clock sources for other devices. They serve as intermediaries between the Grandmaster Clock and ordinary clocks (end-user devices).

Ordinary clocks (members): Ordinary Clocks represent the end-user devices within the PTP network. These devices synchronise their clocks to the time provided by the Boundary Clocks or the Grandmaster Clock. Ordinary Clocks ensure that all devices in the network maintain consistent and highly accurate time.

PTP synchronisation process

Let us now discuss how the PTP synchronisation process works.

The PTP network comprises one or more communication devices, with a single network connection provided by a Grandmaster Clock device.

The simplified illustration of this process is shown below.

PTP Messages and Timestamp Exchange

Figure 2: PTP messages and timestamp exchange

The Grandmaster Clock generates an accurate time signal. This accurate time signal is transmitted over the Ethernet network in the form of PTP messages. These messages contain the time value of the Grandmaster Clock. The messages are received by the slave devices in the network, which can include both Boundary Clocks and Ordinary Clocks.

As the PTP messages propagate through the network, each device timestamps the message when it receives it. By comparing the timestamped time in the PTP message with its own local clock time, each device calculates the clock offset and delay incurred by the message as it traverses the network. Using this offset and delay information, the slave devices adjust their internal clocks to align with the time of the Grandmaster Clock. This adjustment occurs gradually to ensure a smooth transition.

The process of message exchange, timestamping, and clock adjustment is iterative and continuous, ensuring that all devices in the network remain synchronised with sub-microsecond precision.

Challenges addressed by PTP synchronisation

As described earlier, PTP synchronisation provides solutions to several factors that can lead to timing inconsistencies in Ethernet network systems, including:

Time mismatch: Devices on a network inherently have different internal clocks, leading to time mismatches.

Hardware’s nature: Variations in hardware components can cause timing inconsistencies.

Power fluctuations: Power interruptions and fluctuations can affect the accuracy of device clocks.

CPU load: Processing load on devices can impact their clock accuracy.

Interrupt latency: The time it takes for devices to respond to external events can introduce timing errors.

PTP synchronisation modes for Ethernet cameras

When it comes to Ethernet cameras, PTP synchronisation can be implemented in two primary modes:

Master-slave synchronisation: In this mode, one Ethernet camera is designated as the master clock, while the other cameras act as slaves. The master clock sends its precise clock signal to the slave cameras, which then adjust their internal clocks to synchronise with the master. This mode is particularly useful when one camera needs to serve as a reference for others.

Auto-synchronisation: In auto-synchronisation mode, the Ethernet cameras negotiate among themselves to determine which camera will function as the master clock. This negotiation process involves the cameras exchanging clock signals and comparing their results to identify the most accurate clock source. Once the master is selected, all cameras synchronise their clocks to match the chosen master. Auto-synchronisation is convenient in scenarios where the selection of a single master camera can change dynamically.

Benefits of PTP Time synchronisation in Ethernet cameras

The advantages of implementing PTP time synchronisation in Ethernet cameras are numerous and extend to various applications:

  1. Frame alignment

PTP ensures that frames captured by different Ethernet cameras are precisely synchronised. This precise synchronisation allows for seamless alignment and coordination in applications like video streaming and industrial automation. When events need to be reconstructed or analysed in real time, frame alignment is crucial to maintain data integrity.

  1. Multi-camera coordination

In setups involving multiple Ethernet cameras, PTP guarantees that images and videos are accurately timestamped. This precise timing enables synchronisation and correlation of events across cameras, a vital requirement for applications such as 3D reconstruction and motion analysis. Multiple cameras can work together seamlessly, capturing different perspectives of the same scene with perfect synchronisation.

  1. Real-time control and coordination

For applications requiring real-time control and coordination across networked devices, PTP is indispensable. Robotics and automation systems, for example, rely on distributed systems operating on the same time scale to ensure smooth, synchronised operation. PTP enables these systems to communicate and respond in real time, enhancing their precision and reliability.

  1. Reduced jitter and latency

PTP minimises clock drift and network-induced jitter, resulting in smoother and more stable data transmission. This is crucial for real-time applications where even slight delays or inconsistencies can lead to performance issues.

  1. Improved data integrity

Ethernet cameras that rely on timestamped data, PTP ensures that the data is accurately timestamped, facilitating accurate analysis, correlation of events, and historical record-keeping.

Final thoughts

PTP synchronisation is a fundamental aspect of Ethernet camera technology that empowers these devices to deliver sub-microsecond accuracy in timing and synchronisation. Its master-slave architecture and auto-synchronisation modes ensure that Ethernet cameras can work together seamlessly, yielding benefits such as frame alignment, multi-camera coordination, and real-time control. As technology advances, PTP will continue to play a pivotal role in enabling Ethernet cameras to meet the stringent demands of various industries and applications such as Autonomous Mobile Robots, Smart farming, Smart traffic, Telepresence robots, Patient care, and Autonomous shopping.

PTP synchronised Ethernet cameras offered by e-con Systems

e-con Systems offers a range of cutting-edge products, including the RouteCam series of GigE cameras. These cameras are designed to take full advantage of PTP synchronisation, ensuring highly accurate timestamped data in various applications. It provides high-resolution imaging even in low light conditions and supporting cable lengths of up to 100 meters.

e-con Systems, with 20+ years of experience, has designed, developed, and manufactured GigE cameras like:

RouteCAM_CU22_IP67 – This rugged IP67-rated Full HD Power-over-Ethernet (PoE) camera with IEEE 802.3af compliance is designed for demanding environments. Based on the Sony STARVIS IMX662 1/2.8″ CMOS image sensor, it excels in challenging conditions while maintaining exceptional image clarity.

RouteCAM_CU20 – This 2MP HDR GigE camera (also IEEE 802.3af compliant), featuring the Sony STARVIS IMX462 sensor, delivers exceptional image quality. Its GigE interface allows seamless video data transfer over cable lengths of up to 100 meters. As an ONVIF-supported camera, it ensures reliable image and control data transmission over a wired LAN network.

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