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Application Information
PTP Graphs Application
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PRISM MPI-MPX User Manual
should converge on the same value. This value represents the average network
delay between the master and slave for the traffic in both directions.
If the network delay is too unstable, then the PTP might never lock. This appears
as large variations on this trace.
– Master Slave Variation: The master-to-slave variation graph is derived from the
same data as the master-to-slave delay. The absolute value of the changes in
delay are filtered according to RFC1889 and displayed. This display then shows a
measure of the variation of the network delay. A low value indicates a PTP slave is
likely to quickly lock, a large value indicates it could be difficult for a PTP slave to
lock.
– Slave to Master Delay: This graph indicates the difference in the time stamps for
the PTP Delay Request messages that go from the slave to the master. This
display indicates effects of the upstream network delay and adjustments made
to the slave clock. After the slave is locked and the timing is stable, the
perturbations on this graph are largely due to network variations. Traffic often
causes some messages to be delayed so the maximum delay increases.
As the PTP is locking, the slave clock adjusts, so the trace may have large swings
or jumps. As the system locks, the master-to-slave and slave-to master-delays
should converge on the same value. This value represents the average network
delay between the master and slave for the traffic in both directions.
If the network delay is too unstable, then the PTP might never lock. This appears
as large variations on this trace.
– Slave to Master Variation: The master-to-slave variation is derived from the same
data as the master-to-slave delay. The absolute value of the changes in delay are
filtered according to RFC1889 and displayed. This display then shows a measure
of the variation of the network delay. A low value indicates a PTP slave is likely to
quickly lock. A large value indicates it could be difficult for a PTP slave to lock.
– PTP Phase Lag: The graph shows the error in the slave clock phase as measured
by the PTP time stamps. This value is used to adjust the slave clock to drive the
error toward zero.
The PTP phase lag is the phase error of the phase-locked loop, which controls the
slave clock. The phase lag is a reasonable estimate of how well the PTP slave is
locked to the master; however, the phase lag does not indicate if there is any
asymmetry in the network.