What is the PTP Grandmaster Clock?

TP is a time synchronization protocol defined in IEEE 1588 version 2 (ITU-T G.8275.1) for devices across a network. Using PTP, you can synchronize distributed clocks with nanoseconds accuracy. The clocks in the PTP-enabled devices follow a master-slave hierarchy. The slaves are synchronized to their masters. The top-level master is called the grandmaster. The grandmaster clock is synchronized with a Global Positioning System (GPS).

In a PTP-enabled network, synchronization between master and slave clocks occurs through a series of message exchanges. The master first sends a synchronization message to the slave. In response, the slave sends a delay request to the master, which then replies with a delay response. This process measures the network delay and ensures that the slave clock is accurately synchronized with the master clock. This synchronization method is known as one-step synchronization.  

What is the PTP Grandmaster clock?

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.

Grandmaster Clocks: The Heartbeat of a Network  

As the demand for highly accurate network time sources continues to rise—spanning industries from radio access to national defense—Precision Time Protocol (PTP) synchronization has become essential for maintaining precise timing across local area networks. At the core of PTP systems lies the grandmaster clock, a critical component responsible for distributing standardized time information to all other clocks within the network.  

Grandmaster clocks ensure accurate and stable synchronization, whether they are locked to Global Navigation Satellite Systems (GNSS) or operating in holdover mode when satellite signals are unavailable. Their ability to maintain precise timing, even in challenging conditions, makes them indispensable for modern time-sensitive applications.

What is Grandmaster Time?

Grandmaster clocks receive UTC-based time information from an external time reference, most commonly a GNSS satellite source. The GNSS-receiver and a PTP engine deliver a PTP service over Ethernet ports. This is then distributed downstream to other clocks.

PTP Clock Modes  

PTP-enabled devices can operate in different clock modes, including:  

- Ordinary Clock (OC): A clock with a single PTP-enabled port that maintains the timescale of the domain. It can function as either a master or a slave.  

- Boundary Clock (BC): A clock with multiple PTP-enabled ports that maintains the timescale of the domain. Each port can operate as a master or a slave.  

To determine the most accurate and reliable master clock in a distributed network, PTP devices run the Best Master Clock (BMC) algorithm. This algorithm compares attributes from multiple clocks to identify the highest-quality time source.  

The BMC algorithm is responsible for:  

- Selecting the best master clock among those announced in the network.  

- Comparing a newly discovered foreign master with the local clock to determine if a change in master selection is necessary.  

For a detailed specification of the BMC algorithm, refer to the ITU-T G.8275.1 standard.