System Management
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Basic System Configuration Guide
3HE 11010 AAAC TQZZA Edition: 01
• phase tracking
• frequency tracking
• holdover
• free-run
When a port’s ACR state is normal, phase tracking, or frequency tracking, the
recovered ACR clock is considered to be a qualified reference source for the SSU. If
this reference source is being used, then transitions between any of these three
states will not affect SSU operation.
When a port’s ACR state is free-run or holdover, the recovered ACR clock is
disqualified as a reference source for the SSU. If this reference source is being used,
then transitions to either of these two states cause the SSU to drop the reference and
switch to the next highest prioritized reference source. This can potentially be SSU
holdover.
6.4.3.2 ACR Statistics
The system collects statistics on all ACR-capable ports. ACR statistics detail how the
digital phase locked loop (DPLL) is functioning in one or more ACR instances in the
adapter card. ACR statistics assist with isolating a problem during degraded
synchronization performance or with anticipating future issues.
Within the DPLL, there are two values that contribute to ACR statistics:
• DCO frequency
• input phase error of each 2-second update interval
The DCO is the digitally controlled oscillator that produces the regenerated clock
signal. The input phase error is the correction signal that provides feedback to the
DPLL in order to tune the DCO output. The input phase error should approach zero
as the DPLL locks in to the source timing information and stabilizes the output.
The continuous 2-second updates to the output DCO frequency are directly applied
as the clock output of the ACR instance. ACR statistics allow you to view the mean
frequency and the standard deviation of the output DCO frequency.
During every 2-second update interval, the input phase error and the output DCO
frequency are recorded. The input phase error mean, input phase error standard
deviation, output DCO mean (Hz and ppb), and output DCO standard deviation are
calculated every 60 seconds.
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