Precision Time Protocol (PTP)

What is Precision Time Protocol (PTP)?

Key features and components of PTP include:

• Hierarchy: PTP operates in a hierarchical manner with grand source clocks (GSC), providing the reference time, and boundary and transparent clocks synchronizing their time with GSC.
• Best clock source algorithm: This algorithm allows the devices to select the best source clock based on factors and metrics such as clock quality, stability, and network topology.
• Sync messages: PTP uses these messages to maintain synchronization between devices.
  • Delay request and response messages: These messages are exchanged between the source and sink clocks to measure the network delay and provides additional data needed for accurate synchronization.
• Timestamping: PTP uses precise timestamping to measure the exact time at which messages are sent and received, improving the overall accuracy of synchronization and enabling accurate calculation of network delays.
• Profiles: PTP supports multiple profiles and can be selected depending on the specific application requirements, for instance, the default profile for general use and the telecom profile for telecommunications etc. 

PTP-aware devices have one of four internal time keeping mechanisms, called clocks, that may exist in a network:

• Grand source clock (GSC): High-precision clock used as a time source for the rest of the network. Typically, a device with a built-in GNSS (Global Navigation Satellite System) receiver as the reference time source
• Boundary clock (BC): A network device that is a sink for upstream PTP clocks and a source for downstream clocks. It has an embedded high-precision clock and oscillator and synchronizes its own clock using PTP. It also helps extend PTP synchronization across large or complex networks. Boundary clock functionality is a prerequisite for audio-video bridging (AVB) support
• Transparent clock (TC): Intermediate time-aware device that is neither a sink nor a source. It modifies received PTP synchronization messages from upstream clocks, adds resident time to packet’s existing timestamp, then transmits the modified PTP synchronization messages to downstream PTP devices.
• Ordinary clock: A network device, typically an end station that is a sink for upstream clocks. It has a clock embedded in a PTP client device requiring synchronization with a reference clock via the network. Multimedia broadcast equipment, streaming appliances, audio mixers are some of the types of devices that function as PTP ordinary clocks.

PTP has been heavily utilized by the telecommunications industry for a long time. Today, private 5G (P5G) networks are becoming more prevalent to support critical applications and services that require the PTP level of precision and accuracy. Whether for monitoring, control, communication, or video broadcasting, accurate time synchronization is fundamental to the smooth operation of complex systems and the prevention of errors.

PTP is not only beneficial for Telco or public and private 5G networks but also for emerging line-of-business requirements such as AI inferencing, 5G quality of service  , video broadcasting, and other latency-sensitive applications or use cases. It ensures data consistency, real-time video synchronization, and cloud infrastructure and AI data center reliability. PTP provides the accurate and extremely precise time synchronization critical across various industries like financial sector (to prevent fraudulent trading activities), manufacturing sector (for logistics and inventory management), media/entertainment (audio/video synchronization for streaming), and critical government missions . For businesses to grow, innovate and deliver it is imperative to adopt PTP.