Reference Monitoring: Phase

The quality of input references can be assessed by comparing their phase offsets against the current system reference, and against each other. This is called Reference Monitoring.

Reference Monitoring helps to understand and predict system behavior, and is an interference mitigation tool. It can also be used to manually re-organize reference priorities e.g., by assigning a lower reference priority to a noisy reference or a reference with a significant phase offset, or to automatically failover to a different reference if certain quality thresholds are no longer met.

NetClock allows Reference Monitoring by comparing the phase data of references against the System Ontime Point. The phase values shown are the filtered phase differences between each input reference 1PPS, and the internal disciplined 1PPS.

The data is plotted in a graph in real-time. The plot also allows you to display historic data, zoom in on any data range or on a specific reference. A data set can be exported, or deleted.

To monitor the quality of references, navigate to TOOLS > SYSTEM: Reference Monitor. The Reference Monitor screen will display:

On the left side of the screen, Status information is displayed for the System and the References. Note that the Reference Status panel also displays the latest PHASE OFFSET reading (1) for active references against the System Ontime Point. The reading is updated every 30 seconds.

This Reference Phase Offset Data is plotted over time (abscissa) in the Reference Monitor panel in the center of the screen. Use the check boxes in the References panel (2) to select the reference(s) for which you want to plot the phase offset data. Use the handles (3) to zoom in on a time window.

The scale of the axis of ordinate (4) is determined by the largest amplitude of any of the references displayed in the current time window. Use the checkboxes in the References panel on the right to remove references from the graph, or add them to it.