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Precision Time Protocol (PTP) Overview

SUMMARY Precision Time Protocol (PTP) is a time-based protocol, designed to distribute precise time and frequency over packet-switched Ethernet networks.

PTP, also known as IEEE 1588v2, is a packet-based technology that enables the operator to deliver synchronization services on packet-based mobile backhaul networks. IEEE 1588 PTP (Version 2) clock synchronization standard is a highly precise protocol for time synchronization that synchronizes clocks in a distributed system. The time synchronization is achieved through packets that are transmitted and received in a session between a timeTransmitter clock and a timeReceiver clock. When a clocks serves as a source of time, it is known as a timeTransmitter clock. When a clock may synchronize to another clock, it is called a timeReceiver clock. The following list explains these clocks in detail:

  • TimeTransmitter clock—The timeTransmitter clock transmits the messages to the PTP timeReceiver clocks (also called timeReceiver node or boundary node). This allows the timeReceiver clocks to establish their relative time distance and offset from the timeTransmitter clock (which is the reference point) for phase synchronization. Delivery mechanism to the timeReceiver clocks is either unicast or multicast packets over Ethernet or UDP.

  • TimeReceiver clock—located in the PTP timeReceiver (also called timeReceiver node), the timeReceiver clock performs clock and time recovery operations based on the received and requested timestamps from the timeTransmitter clock.

The system clocks can be categorized based on the role of the node in the network. They are broadly categorized into ordinary clock, boundary clock, grandmaster clock and transparent clock. The following list explains these clocks in detail:

  • Boundary clock—The boundary clock has multiple PTP ports in a domain and maintains the timescale used in the domain. The boundary clock operates as a combination of the timeTransmitter and timeReceiver clocks. The boundary clock endpoint acts as a timeReceiver clock to the timeTransmitter clock, and also acts as the timeTransmitter to all the timeReceiver clocks reporting to the boundary endpoint.

  • Ordinary clock—The ordinary clock has a single PTP port in a domain and maintains the timescale used in the domain. It operates either as a timeTransmitter or timeReceiver clock.

  • Transparent clock—Transparent clocks measure and adjust for packet delay. The transparent clock computes the variable delay as the PTP packets pass through the switch or the router.

  • Grandmaster clock—Grandmaster clock is the primary source of time and provides root time reference in PTP. It is connected to a reliable time source such as GPS. All other clocks directly or indirectly synchronize with the grandmaster clock. The grandmaster clock is always configured as a timeTransmitter clock.

See the Feature Explorer page to confirm platform and release support for specific features.

Note:

  • Unified in-service software upgrade (unified ISSU) is currently not supported when clock synchronization is configured for PTP and Synchronous Ethernet on the MICs and Enhanced MPCEs on MX240, MX480, MX960, MX2010, and MX2020 routers.

  • To switch between the PTP and Synchronous Ethernet modes, you must first deactivate the configuration for the current mode and then commit the configuration. Wait for a short period of 30 seconds, configure the new mode and its related parameters, and then commit the configuration.

  • PTP configuration might not work properly when MX10008 Router with JNP10K-LC2101 Line card and Hypermode Enabled. Hypermode can be enabled by default when MX10008 Router has Switch Fabric Board 2 (SFB2), or by using the command set forwarding-options hyper mode. Hence, such PTP interfaces (timeReceiver, timeTransmitter, stateful) are unsupported.