1-67
Cisco ONS 15600 SDH Troubleshooting Guide, R8.0
July 2010
Chapter 1 General Troubleshooting
1.8.2 Holdover Synchronization Alarm
1.8.2 Holdover Synchronization Alarm
Symptom
The clock is running at a different frequency than normal and the HLDOVRSYNC alarm
appears. Holdover occurs when the node is provisioned for external or line timing and both of the
provisioned references fail. The timing switches to the internal Stratum 3E clock on the TSC card.
describes the potential cause of the symptom and the solution.
Table 1-18
ONS 15600 Switches Timing Reference
Possible Problem
Solution
The optical or building
integrated timing
supply (BITS) input is
receiving loss of signal
(LOS), loss of frame
(LOF), or AIS from its
timing source.
Clear the alarm and set up the timing source to a reliable source.
To clear an LOS (BITS) alarm, see the
“LOS (BITS)” alarm on page 2-85
.
To clear an LOF (BITS) alarm, see the
“LOF (BITS)” alarm on page 2-81
.
To clear an AIS (BITS) alarm, see the
.
Refer to the procedure for setting up timing in the
Cisco ONS 15600 SDH
Procedure Guide
.
The optical or BITS
input is not functioning.
Synchronization status
messaging (SSM)
message is set to do not
use (DUS).
The Synchronization Status Message (SSM) Changed to Do Not Use (DUS)
condition occurs when the synchronization status message quality level is
changed to DUS.
The port that reports the condition is not at fault. The condition applies to the
timing source. SSM-DUS prevents timing loops by providing a termination
point for the signal usage.
To clear the SSM-DUS alarm, see the
“SSM-DUS” condition on page 2-111
.
SSM indicates a
Stratum 3 or lower
clock quality.
The input frequency is
off by more than 15
ppm.
Set up the timing input to a reliable timing source. Refer to the procedure for
setting up timing in the
Cisco ONS 15600 SDH Procedure Guide
.
The input clock
wanders and has more
than three slips in 30
seconds.
Table 1-19
Holdover Synchronization Alarm
Possible Problem
Solution
The primary and
secondary reference
inputs have failed.
This alarm is raised when the primary and secondary reference inputs fail.
See the
“HLDOVRSYNC” condition on page 2-66
for a detailed description.
Note
The ONS 15600 SDH supports holdover timing per
Telcordia GR-436-CORE when provisioned for external timing.
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