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    Enterprise Profile for the Precision Time Protocol

    The Precision Time Protocol (PTPv2), as defined in IEEE 1588-2008 (PTPv2) standard, adds unicast communications to optimize network traffic, adds transparent clocks, improves accuracy, and defines the use of PTP profiles to specify parameters for particular applications and scenarios.

    The need for PTP in the enterprise and financial markets is growing, due to the need to time stamp events on different systems within a large enterprise network with a range of latencies and delays. Expected accuracies range from 100 microseconds to 500 nanoseconds to the grandmaster. These networks commonly prefer multicast communications. A profile for PTP enterprise deployments based on PTPv2 has been created by IETF to meet this need.

    The PTP enterprise profile feature adds the following aspects:

    • IPV4 multicast transport, includes dynamic detection of streams, rather than explicit configuration.
    • Parameter control that is consistent with the defined enterprise profile draft.
    • Identification of PTP remote devices using the clock-identity received in the PTP packet.

    The PTP enterprise profile can be enabled, which is similar to the existing operation of PTP clock synchronization; when enterprise profile is enabled, all other profiles are disabled.

    PTP enterprise profile in ACX Series routers include the following options:

    1. Support for boundary clock (BC) mode.
    2. When enterprise profile is used, Unicast negotiation is disabled.
    3. Support for one-step clock mode with end-to-end delay measurements; support for two-step slave without two-step master mode.
    4. Alternate timescales are not supported.
    5. PTP over IP and UDP packet encapsulation:
      1. Standard PTP over IPv4 and UDP, as per Annexes D and E in IEEE 1588v2.
      2. Reception and transmission of multicast announce and Sync PTP packets.
      3. Reception of multicast or unicast delay request packets for ACX master ports; the delay response is sent with the same multicast and unicast transmission to match the request.
      4. Transmission of unicast delay request packets for ACX slave ports (ACX does not transmit multicast delay request packets).
      5. IPv4 multicast address used for PTP is
      6. Interfaces may be trunk or access ports–so the traffic may or may not have a VLAN.
    6. Dynamic master and slave detection, as announce and delay request packets are received:
      1. Streams identified by clock-identity, rather than IP address.
      2. Up to four remote master clocks are allowed and the clock source is selected by the best master clock (BMC) algorithm.
      3. Up to 512 remote slave clocks are allowed.
      4. When the number of masters or slaves have reached the limit, any new incoming remote devices are ignored.
      5. A timeout mechanism is used if messages are no longer being received from a remote device; streams that are no longer receiving packets are removed.

    The announce packet rate is fixed at 1 PPS. The announce receipt timeout interval is three Announce intervals (3 seconds) for all masters. These values cannot be configured.

    Sync packet rates range from once every 16 seconds to 128 PPS; the default is 16 PPS. Delay request packet rates range from 8 PPS to 64 PPS.

    Modified: 2018-03-12