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Assisted Partial Timing Support on ACX7024 and ACX7024X Routers

Assisted Partial Timing Support (APTS) is a GNSS backed by PTP delivering accurate timing and synchronization in mobile backhaul networks. This topic talks about the APTS support on ACX7024 and ACX7024X routers.

ACX7024 and ACX7024X routers act as Telecom Boundary Clock for Assisted partial timing support (T-BC-A). The router locks to GNSS as a primary source. When GNSS loses lock, it operates in a frequency or phase backup mode by deriving the time information from a G8275.2 packet timeReceiver.

You can configure the clock class threshold. The system will consider the upstream PTP timeTransmitter as a backup source only if the timeTransmitter's clock class is less than or equal to the set threshold value.

If GNSS loses lock and PTP is unavailable or not ready, then the system moves into a holdover-in-spec state with the internal clock and continues to be in that state until the holdover timer expires. You can configure the holdover time using the holdover-in-spec-duration option under the [set protocols ptp] hierarchy. Once GNSS is available, the router locks back to it.

Note:

Once the system enters the holdover state, it remains in that state until GNSS is restored, even if PTP becomes available again.

The supported APTS features include:

  • Both G.8275.1 and G8275.2 timeTransmitter ports are supported, and up to four G.8275.2 timeReceiver ports can be configured as the backup path for APTS.

  • Up to 512 PTP over IPv4 timeTransmitter streams are supported and up to 128 PTPoE timeTransmitter streams are supported. PTP over IPv4 and PTPoE are supported simultaneously.

  • Four PTP over IPv4 timeReceiver streams are supported when APTS is configured.

  • PTP over IPv4 timeReceiver configuration is supported for interfaces that belong to a routing-instance.

  • Unicast negotiation is enabled by default in APTS mode.

  • APTS is supported for 100 G, 50 G, 40 G, 25 G, 10 G, 1 G ports.

TimeReceiver Selection when GNSS is Down

During normal operation with GNSS active, the system selects the best PTP timeReceiver using the G.8275.2 BMCA and calculates a base phase offset relative to GNSS. If GNSS fails, it switches to the PTP source and adjusts phase using the stored base offset with only incremental changes. When BMCA changes the active timeReceiver, the previous timeReceiver's offset is reset, and the new timeReceivers follow the standard G.8275.2 profile with full phase correction. If the phase offset exceeds 1.1 µs (microseconds), the system raises an alarm and enters holdover until GNSS is restored. For the original timeReceiver, this threshold applies to the delta offset, while for the new timeReceivers it applies to the entire phase offset.

Configuration

To support this feature on ACX7024 and ACX7024X, you need an APTS node with GNSS source configured at the [edit chassis synchronization] hierarchy level and PTP boundary clock configured at the [edit protocols ptp] hierarchy level as shown below.

  1. Configure ptp-mode to enable PTP functionality:

  2. Configure GNSS settings:

  3. Configure PTP. Note that the clock-mode is set to boundary clock and the base profile is set to G.8275.1 in this configuration for downstream timeReceivers. The configuration [set protocols ptp apts] is required when configuring boundary clock with APTS.

    Optionally configure the domain used for APTS profile:

    You can enable PTP on an interface that belongs to a routing instance:

  4. (Optional) Configure holdover-in-spec-duration settings by specifying the time in minutes:

  5. (Optional) Configure the clock class threshold of the upstream PTP timeTransmitter to a value between 1 and 255.

    The system will consider the timeTransmitter as a backup only if its clock class is less than or equal to the set threshold value. If this parameter is not configured, the default is value is set to 248.

Verification

  • Verify the PTP configuration:

  • Verify PTP lock status:

  • Verify PTP clock details by executing the show ptp clock detail command.

  • Verify the available upstream PTP timeTransmitter details by executing the show ptp all-master-clock detail command.

  • Verify PTP port details by executing the show ptp port detail command.

  • Verify PTP statistics details by executing the show ptp statistics detail command.