Phase Adjustment Mitigation in Hybrid Mode

Benefits

• Maintain service integrity by ignoring erroneous phase adjustments due to GNSS interference.

• Enhance synchronization stability by preventing service disruptions caused by significant phase jumps from upstream PTP nodes.

• Offer control over synchronization behaviors with configurable phase-error limits, allowing precise management of timing and synchronization thresholds.

• Facilitate recovery from upstream discrepancies through grace period management, preventing smaller phase jumps during normalization.

• Maintain synchronization integrity by integrating synchronous Ethernet holdover actions, preventing unintentional clock source changes during PTP holdover conditions.

Overview

The Phase Adjustment Mitigation feature in PTP and synchronous Ethernet hybrid configurations is designed to enhance the robustness of timing and synchronization by addressing significant phase jumps. Configure thresholds to determine when phase offsets should be ignored when coming in from an upstream T-GM or T-BC, thus preventing disruptive changes in time-sensitive deployments. Set phase-error limits using the CLI statement protocols ptp phase-error-limit relative-threshold <nanoseconds> to ensure network stability even when upstream PTP nodes experience phase disturbances. When thresholds are exceeded, the system ignores these phase changes, safeguarding against erroneous time propagation, particularly in scenarios involving GNSS interference.

In addition to ignoring phase adjustments, the PTP node will go into holdover if the phase offset remains too high for over 10 servo measurement windows (MWs). When going into holdover, the node will transmit the same clock class as it would ordinarily under the current servo behavior. This means that any timeTransmitter ports on the PTP node will transmit a clock class of 135 to downstream PTP nodes if locked to a synchronous Ethernet source. If synchronous Ethernet is not locked while the servo is in holdover, a clock class of 135 is transmitted for the first 5 minutes and then clock class 165 is transmitted.

Note:

The following conditions should be met to ensure the feature is active:

• The line card of the selected timeReceiver has been up for 30 minutes or more in a distributed PTP node.
• The feature has been configured at least five minutes ago.
• The PTP servo has been phase aligned for five minutes or more and is not in the holdover state because of this feature.
• The calculated phase adjustment is not because of a change in PTP timeTransmitter or synchronous Ethernet source.
• An asymmetry configuration change hasn’t occurred in the past three measurement windows (MWs) since the change was seen by the PTP servo. If an asymmetry configuration change is made, it can cause the threshold to be exceeded on downstream nodes where the Phase Adjustment Mitigation feature is configured.

Additionally, the feature integrates synchronous Ethernet holdover actions, crucial during PTP holdover conditions. When PTP servo enters holdover due to a high phase offset, use the statement protocols ptp phase-error-limit force-synce-holdover to force synchronous Ethernet sources into holdover. This action prevents clock source changes during critical holdover periods, maintaining synchronization stability across the network. The integration between PTP and synchronous Ethernet during holdover is pivotal for consistent time propagation, preventing unintentional shifts in synchronization that could lead to service disruptions. You can configure protocols ptp phase-error-limit max-holdover-time <minutes> to specify a time limit during which the PTP servo stays in holdover after receiving a phase adjustment exceeding the threshold.

Monitoring the Phase Adjustment Mitigation feature is equally important. Utilize the statements show ptp phase-error-monitoring status and show ptp global-information to track the status of phase-error monitoring and configuration changes. These monitoring tools provide insights into synchronization behaviors and help ensure phase-error parameters are precisely managed. This capability is essential for maintaining synchronization integrity, especially during recovery periods where grace period management ignores smaller phase jumps post-normalization. This mechanism bolsters system resilience, facilitating recovery from upstream discrepancies.

Note:

Use Feature Explorer to confirm platform support for the Phase Adjustment Mitigation feature.

Implementation Considerations

In distributed PTP topologies, the Phase Adjustment Mitigation feature operates primarily at the first T-BC. It focuses solely on PTP-originated phase changes, without addressing adjustments due to synchronous Ethernet frequency drifts.

Platform-Specific Phase Adjustment Mitigation Behavior

Use Feature Explorer to confirm platform and release support for specific features.

Use the following table to review platform-specific behaviors for your platform:

Table 1: Platform-Specific Behavior

Platform	Difference
MX Series	Distributed PTP topologies refer to topologies containing distributed PTP nodes. The platforms that use distributed PTP are MX204, MX240, MX480, MX960, MX2008, MX2010, and MX2020. Not all of these platforms necessarily support the Phase Adjustment Mitigation feature. Refer to the Feature Explorer.