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Understanding the Precision Time Protocol Enterprise Profile

 

The enterprise profile is based on Precision Time Protocol (PTPv1) as defined in IEEE 1588-2002. This profile was designed to distribute system time of day (TOD) and clock frequency from a grand master clock to client clocks within the same network and clock domain, and to use multicast communications. The enterprise profile PTPv2 is not backwards compatible with PTPv1.

With the enterprise profile, you can use either boundary or ordinary clocks. Up to 512 downstream client clocks are supported. Slave clock ports can recover clocks from one-step or two-step master clocks, but master clocks only support one-step PTP.

The enterprise profile supports PTP over IPv4 and UDP encapsulation, which includes the following functionality:

  • Reception and transmission of Multicast Announce and Sync PTP packets.

  • Reception of multicast or unicast Delay Request packets for the master clock interfaces.

    The Delay Response is sent with the same multicast or unicast transmission to match the request.

  • Transmission of unicast Delay Request packets for the client clock interfaces.

    The switch will not transmit Multicast Delay Request packets.

  • IPv4 Multicast address of 224.0.1.129 for PTP.

  • PTP Interfaces can be trunk or access ports, so the traffic might or might not be part of a VLAN.

The enterprise profile supports dynamic master clock interface and client clock interface detection as Announce and Delay Request packets are received and supports the following functionality:

  • Streams are identified by the clock identity, rather than the IP address.

  • Up to four remote master clocks that use the best master clock (BMC) algorithm to select the clock source.

  • Up to 512 remote client clocks with up to 64 logical interfaces.

  • Remote devices are ignored when the number of master and client clocks has reach the limit.

    If messages are no longer being received from a remote device; a timeout mechanism is used. Streams are removed if they are no longer receiving packets after a default value of 30 seconds.

To support a 1-Gigabit Ethernet connection to a grandmaster clock, you can use a special interface that is labeled PTP on the faceplate of the QFX10002 switch. This interface is named ptp0 in the Junos OS CLI. This interface only supports encapsulated PTP, ARP, and PING packets to support the grandmaster clock connection. Non-PTP traffic is not supported. You can configure this interface as a client clock interface to connect to a grandmaster but not as a tagged interface. You can, however, configure 10-, 40-, and 100-Gigabit Ethernet interfaces as master clock, client clock, and in tagged and untagged configurations.

With the enterprise profile enabled, there are restrictions on which parameters you can configure or cannot configure.

With the enterprise profile enabled, you can configure the following parameters:

  • Priority1

    The range is from 0 to 255, and the default value is 128.

  • Priority2

    The range is from 0 to 255, and the default value is 128.

  • Domain number

    The range is from 0 to 127, and the default value is 0.

  • Clock mode

    Clock mode can be ordinary or boundary.

  • Delay request

    The Range -7 to +7 seconds, and the default value is 0 (1pps).

  • Sync interval

    The range is -7 to +4 seconds, and the default value is 0 (1pps).

With the enterprise profile enabled, you cannot configure the following parameters:

  • Announce interval

    Default value is 0 (1pps).

  • Announce timeout

    The announce receipt timeout interval is set for three announce intervals for preferred master clocks, and four announce intervals for all other master clocks. All master clocks will be treated as preferred master clocks, so the announce receipt timeout interval is set to three announce intervals.

  • Unicast negotiation