What is PTP？

What is PTP?

PTP (Precision Time Protocol) also called IEEE 1588v2, is a packet-based technology for high-precision time synchronization. Initially developed to enhance synchronization in telecommunications, it now provides critical services for mobile backhaul networks and various distributed systems, ensuring accurate clock coordination across IP networks.

PTP ensures accurate synchronization of mobile backhaul networks by enabling efficient communication between the master clock and client clocks via timestamped packets. Using hardware timestamps, PTP can achieve nanosecond synchronization accuracy, making it the most accurate time synchronization protocol available.

How does the PTP work?

To enable PTP to be applied to individual devices in the network synchronized with a reference clock. It operates on the following principles:

1. 1. Selection of Synchronization Modes: The PTP protocol supports several synchronization modes, including E2E(End-to-End) mode and P2P(Peer-to-Peer) mode. E2E mode is suitable for short path lengths, P2P mode is suitable for scenarios with long path lengths.

2. 2. Establishment of Master-Slave Relationship: The PTP protocol first establishes a master-slave relationship through interactive messages between the master and slave nodes. The Master Clock periodically sends Sync messages and records the exact time when the message leaves the Master Clock, t1. When the Slave Clock receives the Sync message, it records the time when it receives it, t2. In this way, the basis of time synchronization between the Master Clock and the Slave Clock is established.

3. 3. Measurement of Propagation Delay: The PTP protocol needs to measure and compensate for the propagation delay in the network, that is, the time it takes for a packet to travel through the network. The master clock sends a Delay_Req message, and when it is received, the slave clock then sends a Delay_Resp message, and the master clock then records the time it received the response, t3. The propagation delay can be derived by calculating the difference between t1, t2, and t3, afterward adjusting the time base of the slave clock accordingly.

4. 4. Time Offset Calculation: PTP further calculates the time offset based on the measured propagation delay. Assuming that the network has a symmetric propagation delay, the propagation time is the average time of the synchronization and delay request messages. By calculating four timestamps (t1, t2, t3, and t4—where t4 is the time the Slave Clock sends the Delay_Resp message), PTP can estimate the time offset between the Slave Clock and the Master Clock. The time base of the slave clock is then corrected to synchronize with the master clock based on the assumption that the one-way network delay is half a cycle.

   

    

    

Benefits of PTP

PTP has demonstrated significant advantages in high-precision time synchronization, making it an indispensable choice in modern networks because of the following features.

Security: PTP provides services through a dedicated fiber-optic connection safer than GNSS radio signals. It effectively prevents natural and human interference, ensuring time synchronization security.

Accuracy: PTP achieves nanosecond-level time synchronization accuracy, far exceeding the sub-second accuracy of NTP.

Flexibility: PTP supports a variety of network topologies and can adapt to different needs. In addition, PTP allows multiple PTP services and profiles to coexist on the same physical Ethernet connection, meeting the specific requirements of different applications.

Reliability: The clocks in the PTP system are automatically organized into a master-slave synchronization hierarchy, which ensures that when the master clock fails, the system can quickly switch to the next best clock, thus improving system reliability.

Applications of PTP

As technology advances, potential applications of PTP are becoming even broader.

Industrial Automation: PTP ensures precise time synchronization between devices, sensors, and controllers. For example, robotic arms in a manufacturing line can coordinate their movements with nanosecond precision, leading to more efficient and reliable production processes.

Mobile Communications: PTP is utilized in telecommunication networks for synchronization between base stations to ensure the timing consistency of data across base stations and to improve network capacity and coverage.

Scientific research: Originally used for precision control and measurement in laboratory environments, PTP has expanded into other areas of scientific research.

Financial transactions: In the financial sector, PTP is used to provide high-precision time synchronization services, especially in scenarios such as high-frequency trading and real-time settlement. Furthermore, PTP is the only protocol that can provide the timestamp and traceability required by the MiFID II regulation for financial transactions.