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OSN 500 550 580 V100R008C50 Alarms and Performance Events Reference 02

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The EXT_SYNC_LOS alarm indicates loss of the external clock source in the timing unit.


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 channel of the external clock source that is lost.

  • 0x01: the first channel of the external clock source
  • 0x02: the second channel of the external clock source

Impact on the System

This alarm results in incorrect frame alignment, or a great many bit errors on the receive side and pointer justification events. As a result, services are unavailable.

Possible Causes

The possible cause of this alarm is as follows:

  • The signals of the physical port of the external clock source are lost.


  1. Check whether the cable for inputting the external clock is correctly connected, the cable is loosely connected, or the cable is broken.
  2. Rectify the cable fault. Then, check on the U2000 whether the EXT_SYNC_LOS alarm is cleared.

    If... Then...
    If this alarm is cleared No further action is required.
    If this alarm persists Go to the next step.

  3. Check whether the equipment that provides the external clock is properly operating. If the equipment is not properly operating, replace the equipment.

Related Information


Updated: 2019-01-21

Document ID: EDOC1100020975

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