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OSN 500 550 580 V100R008C50 Alarms and Performance Events Reference 02

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The DDN_LFA is an alarm indicating the loss of frame alignment in the PDH framed E1 services on the electrical interface side. When the electrical interface side fails to receive the frame alignment signals in the framed E1 services, the DDN_LFA alarm is reported.


Alarm Severity Alarm Type


Communication alarm



Impact on the System

  • When the DDN_LFA alarm occurs, the E1 services of the board are unavailable.
  • The DDN_RFA alarm is returned to the opposite end.

Possible Causes

The possible causes of the DDN_LFA alarm are as follows:

  • The DDN equipment interconnected to the path is faulty.
  • The service frame format is incorrectly configured.
  • The board hardware is faulty.


  1. View the DDN_LFA alarm on the U2000 to confirm the relevant board.
  2. Check whether the interconnected DDN equipment works well by performing loopback to the equipment cable. If any fault is found, take priority to remove it, and then check whether the DDN_LFA alarm is cleared.
  3. Check whether the frame format of the E1 signals transmitted from the opposite end is consistent with that specified at the local end. Make sure that the service configuration is correct, and that the frame format of the E1 signals matches each other at the two ends. Then check whether the DDN_LFA alarm is cleared.
  4. If the alarm persists, perform a cold reset on the board. Then check whether the DDN_LFA alarm is cleared.

    If the services travel through the board are not configured with protection, the services are interrupted after the cold reset of the board.

  5. If the alarm persists, the board is faulty. Replace the board. Then the DDN_LFA alarm is automatically cleared.

Related Information


Updated: 2019-01-21

Document ID: EDOC1100020975

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