Configuring the Automatic Clock Source Selection Mode

Context

A switch supports three clock source selection modes: automatic, manual, and forcible. By default, a switch works in automatic clock source selection mode.

When multiple clock sources are available, a switch selects a clock source as its reference clock according to the clock source priority and Synchronization Status Message (SSM) quality level.

Clock source priority

The default priority for a clock source is 0, indicating that this clock source does not participate in clock source selection. To enable the clock source to participate in clock source selection, specify a priority for it.

A lower priority value indicates a higher priority of a clock source.
Clock source SSM quality level

An SSM is a group of codes used to indicate the clock quality level on a synchronized network. SSM reflects the level of synchronous timing signals transmitted on a synchronous timing link. A higher clock accuracy indicates a higher SSM quality level. A device can be configured to select a clock source according to the SSM quality level.

SSM quality levels are sorted in descending order of preference: primary reference clock (PRC), Synchronization Supply Unit A (SSU-A), Synchronization Supply Unit B (SSU-B), SDH equipment clock (SEC), and Do Not Use (DNU).

When multiple clock sources are available on the network, a switch selects a clock source according to the following rules:

If no SSM quality level is specified for clock source selection, the switch selects the clock source to be traced based on the priorities configured for the clock sources.
If an SSM quality level is specified for clock source selection:
1. The switch selects the clock source to be traced based on the SSM quality levels of clock sources.
2. If there are multiple clock sources with the same SSM quality level, the switch selects the clock source to be traced based on the priorities of these clock sources.

Procedure

Run system-view
The system view is displayed.
Run clock clear slot slot-id
The clock source selection mode is restored to automatic.

If a clock source has been selected manually or forcibly, run this command to restore the automatic mode.
Run clock ssm-control on
SSM quality levels are enabled to participate in automatic clock source selection.

By default, SSM quality levels are used for clock source selection.
Run clock run-mode normal slot slot-id
The system clock running mode is set to the normal mode.

By default, the system clock works in normal mode.