The Precision Time Protocol (PTP) is a computer networking protocol for synchronizing Network Element’s clock. It can deliver sub-nanosecond clock accuracy over packet based networks when properly implemented. Thus, making it essential part of 5G mobile networks, measurement and control systems, financial transactions, submarine acoustic arrays or other networks that require accurate time source but do not have direct access to Global Navigation Satellite System (GNSS) signal.
With sub-nanosecond accuracy, PTP is more than a suitable alternative to GNSS/GPS synchronization source. As such, PTP introduces two major advantages. The first is reducing CAPEX, since in a PTP network only a PTP Grandmaster device requires a GPS receiver, contrary to providing an individual GPS receivers to each network node. The other advantage refers to network resiliency. In the event of GPS outage (e.g. due to jamming or spoofing), a PTP Timing source will remain operational. This is vital to mission-critical systems, such as Electric Power grids, Emergency services, Telecommunication services, etc.
Propagating time accurately with PTP is done by exchanging timestamped messages between the device sending the timing signal (Master) and the device receiving it (Slave). These messages allow the Slave device to receive an updated timestamp and the means to calculate the transport latency in order to eliminate any time offset from the Master device. For achieving optimal performance all the devices on the path between Master and Slave units must also support PTP.
While the first version of PTP (IEEE 1588-2002 or PTPv1) is still in use in the industrial sector it is less accurate and not compatible with PTP Version 2 (IEEE 1588-2008) or above. The latest update IEEE 1588-2019 released in November 2019 includes updates to the 2008 publication and is also backward compatible.
With the emerging of 5G networks the demand for high accuracy PTP time sources is increasingly growing. These PTP Grandmasters are equipped with a built-in GNSS receiver and highly stable oscillator such as OCXO or Rubidium. The Grandmaster clocks are tasked with propagating the Timing signal from the GNSS/GPS to the rest of the element in the network. These clocks must continuously maintain stable and accurate Timing signal while locked to GNSS and long duration of Holdover periods with minimal offset when satellite signals are lost.