Terms

  • 1 second, is 1000 ms.
  • 1 millisecond: Network latency is measured in ms, or 1 thousandth of a second 0.001.
  • 1 microsecond: 1 μs (a millionth) of a second. 0.000 001. 1000 μs is 1 ms.
  • 1 nanosecond: 1 ns (a billionth) of a second. 0.000 000 001. 1000 ns is 1 μs.
  • NTP: An older time standard. Can sync time between 10 to 1 ms.
  • PTP: Modern time standard. Can sync time between 10 to 1 ns.
  • PTPv1: - Defined in IEEE 1588-2002
  • PTPv2: - Defined in IEEE 1588-2008, not backwards compatible.
  • PTPv2.1: - Defined in IEEE 1588-2019, is backward compatible.
  • 1588 Clock: A clock in the PTP time domain. Clocks have ports.
  • Terminating Clock: A clock with one port.
  • Ordinary Clock: a clock in a terminating device.
  • Boundary Clock:: a clock in a transmitting device, like an ethernet switch. Connects PTP domains.
  • Transparent Clock: a boundary clock that can correct for delay and modifies the PTP event message.
  • Grandmaster: All clocks sync to this one clock.
  • Master: All clocks in a subdomain sync to the master. The master sync's to the grand master.

Time Terms

  • Epoch: The start of time.
  • Offset: The estimated time between a master clock sending time, and a slave clock receiving it.

Uses

  • Robotics, synchronizing movements.
  • Mobile Phone networks, telemetry, billing, logging
  • Financial Networks, trade settling fairness.
  • Power Networks, to sync to the 60hz grid.
  • Science network, seismic data

Process

After PTP has time from something like a GPS device, it can pass that time along, so long as the devices in the path can mark and read the timestamps

PTP Delay and Offset Calculations

General Messages

  • Announce: Used to determine which Grand Master is selected Best Master

  • Follow_Up: Used to convey a captured timestamp of a transmitted SYNC message

  • Delay_Response: Used to measure delay between IEEE 1588 devices

  • Pdelay_Response_Follow_Up: Used between IEEE 1588 devices to measure the delay on an incoming link

  • Management: Used between management devices and clocks

  • Signaling: Used by clocks to deliver how messages are sent

Event Messages

  • Sync: Used to convey time

  • Delay_Request: Used to measure delay from downstream devices

  • Pdelay_Request: Used to initiate and measure delay

  • Pdelay_Response: Used to respond and measure delay