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OSN 500 550 580 V100R008C50 Alarms and Performance Events Reference 02

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The T_ALOS alarm indicates loss of analog signals at the E1 or T1 interfaces. If no service signals are input at the 2 Mbit/s or 1.5 Mbit/s port, the T_ALOS alarm is reported.


Alarm Severity Alarm Type


Communication alarm



Impact on the System

When the T_ALOS alarm occurs, the PDH services are interrupted.

Possible Causes

Possible causes of the T_ALOS alarm are as follows:

  • The E1 or T1 services are not accessed.
  • The output port of the E1 or T1 interface on the DDF side is disconnected or loose.
  • The cable is faulty.
  • The board is faulty.


  1. View the T_ALOS alarm on the U2000 to confirm the alarmed board.
  2. Check whether the E1 or T1 services in the alarmed path of the board are accessed. After making sure that the services are accessed, check whether the T_ALOS alarm is cleared. If the alarm persists, go to the next step.
  3. If the alarm persists, perform service self-loop (namely, hardware inloop) to the path at the DDF.

    The loopback causes service interruption.

    • If the alarm is cleared, the equipment at the opposite station is faulty. After rectifying the fault, check whether the T_ALOS alarm is cleared.
    • If the alarm persists, go to the next step.
  4. If the alarm persists, check whether the equipment at the opposite station is faulty. If yes, replace the faulty board at the opposite station.

Related Information


Updated: 2019-01-21

Document ID: EDOC1100020975

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