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OSN 500 550 580 V100R008C50 Alarms and Performance Events Reference 02

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The S1_SYN_CHANGE alarm indicates that the clock reference source of the clock board is switched in the S1 byte mode.


Alarm Severity Alarm Type


Equipment alarm


When you view an alarm on the network management system, select the alarm. In the Alarm Details field display the related parameters of the alarm. The alarm parameters are in the following format: Alarm Parameters (hex): parameter1 parameter2...parameterN. For details about each parameter, refer to the following table.

Name Meaning

Parameter 1

Indicates the switching type of the clock source.

  • 0x01: switching of the clock source traced by the system
  • 0x02: switching of 2M phase-locked clock source 1
  • 0x03: switching of 2M phase-locked clock source 2

Impact on the System

When the S1_SYN_CHANGE alarm occurs, the clock reference source of the clock board is switched to other synchronization clock sources in the S1 byte mode, due to the failure in the line source or tributary source or external clock source that is set in the clock source priority table.

Possible Causes

Possible causes of the S1_SYN_CHANGE alarm are as follows:

  • A fiber cut or a cable cut occurs.

  • The external BITS is broken.
  • Clock switching occurs at the uplink station.
  • New clock source is set in the local station.


  1. View alarms on the U2000 to check whether there are alarms that are caused by the following reasons on the local NE.

    If... Then...
    There is the R_LOS, R_LOC, R_LOF, T_ALOS, or EXT_SYNC_LOS alarm. See the corresponding section in this document to clear the alarm.
    There are such alarms as the MS_AIS and B2_EXC, and these alarms are set as conditions that can trigger the clock switching See the corresponding section in this document to clear the alarm.
    There is no alarm Go to the next step.

  2. Clock source protection switching occurs in the network. Check the clock source switching status in the network on the U2000. Check whether there are alarms that can trigger the clock source switching on the upstream NE. If yes, handle these alarms.

Related Information

Updated: 2019-01-21

Document ID: EDOC1100020975

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