About PTP in OKD cluster nodes

The grandmaster clock provides standard time information to other clocks across the network and ensures accurate and stable synchronisation. It writes time stamps and responds to time requests from other clocks. Grandmaster clocks synchronize to a Global Navigation Satellite System (GNSS) time source. The Grandmaster clock is the authoritative source of time in the network and is responsible for providing time synchronization to all other devices.

The boundary clock has ports in two or more communication paths and can be a source and a destination to other destination clocks at the same time. The boundary clock works as a destination clock upstream. The destination clock receives the timing message, adjusts for delay, and then creates a new source time signal to pass down the network. The boundary clock produces a new timing packet that is still correctly synced with the source clock and can reduce the number of connected devices reporting directly to the source clock.

The ordinary clock has a single port connection that can play the role of source or destination clock, depending on its position in the network. The ordinary clock can read and write timestamps.

You can use a cluster host that has dual NIC hardware as PTP grandmaster clock. One NIC receives timing information from the global navigation satellite system (GNSS). The second NIC receives the timing information from the first using the SMA1 Tx/Rx connections on the E810 NIC faceplate. The system clock on the cluster host is synchronized from the NIC that is connected to the GNSS satellite.

Figure 2. Dual NIC grandmaster clock

For 5G telco networks that deliver mid-band spectrum coverage, each virtual distributed unit (vDU) requires connections to 6 radio units (RUs). To make these connections, each vDU host requires 2 NICs configured as boundary clocks.

ts2phc synchronizes the PTP hardware clock (PHC) across PTP devices with a high degree of precision. ts2phc is used in grandmaster clock configurations. It receives the precision timing signal a high precision clock source such as Global Navigation Satellite System (GNSS). GNSS provides an accurate and reliable source of synchronized time for use in large distributed networks. GNSS clocks typically provide time information with a precision of a few nanoseconds.

pmc implements a PTP management client (pmc) according to IEEE standard 1588.1588. pmc provides basic management access for the ptp4l system daemon. pmc reads from standard input and sends the output over the selected transport, printing any replies it receives.

ptp4l implements the PTP boundary clock and ordinary clock and runs as a system daemon. ptp4l does the following:

phc2sys synchronizes the system clock to the PHC on the network interface controller (NIC). The phc2sys system daemon continuously monitors the PHC for timing information. When it detects a timing error, the PHC corrects the system clock.

ubxtool CLI allows you to communicate with a u-blox GPS system. The ubxtool CLI uses the u-blox binary protocol to communicate with the GPS.

gpspipe connects to gpsd output and pipes it to stdout.

gpsd is a service daemon that monitors one or more GPS or AIS receivers connected to the host.

GNSS is a satellite-based system used to provide positioning, navigation, and timing information to receivers around the globe. In PTP, GNSS receivers are often used as a highly accurate and stable reference clock source. These receivers receive signals from multiple GNSS satellites, allowing them to calculate precise time information. The timing information obtained from GNSS is used as a reference by the PTP grandmaster clock.

DPLL provides clock synchronization between different PTP nodes in the network. DPLL compares the phase of the local system clock signal with the phase of the incoming synchronization signal, for example, PTP messages from the PTP grandmaster clock. The DPLL continuously adjusts the local clock frequency and phase to minimize the phase difference between the local clock and the reference clock.