Procedure

1. Query the alarms on the network management and process the related alarms according to the reported alarm information.
   1. Browse the current alarms.

      If ......	then ......
      the network element reports an alarm such as R_LOS, R_LOF, T_ALOS, P_LOS, or IN_PWR_ABN.	Continue to the next step.
      The network element did not report an alarm such as R_LOS, R_LOF, T_ALOS, P_LOS, or IN_PWR_ABN.	Turn to other reasons.

   2. See Alarm and Performance Event Reference for handling alarms such as R_LOS, R_LOF, T_ALOS, P_LOS, or IN_PWR_ABN.
   3. Check to see if the service is back to normal, if not, go to another cause.
2. Cause 1: Fiber breakage causes service interruption.
   1. Use the OTDR meter to measure the fiber and determine whether the fiber is broken by analyzing the line attenuation curve displayed by the meter. Refer to the OTDR operation guide for how to use the meter.

      If ......	then ......
      the line has a broken fiber.	Replace the fiber. Check if the service is back to normal, if not, turn to other reasons.
      There is no fiber breakage on the line.	Refer to other reasons.

3. Cause 2: Excessive fiber and flange attenuation, resulting in service interruption.
   1. Measure the transmit optical power of the opposite-end veneer and the receive optical power of the local-end veneer. For details, see Querying the Optical Power of a Single Board.

      If ......	then ......
      the transmit optical power of the opposite end is abnormal.	Go to cause 3.
      This end receives optical power abnormally.	Proceed to the next step.

   2. The difference between the optical power transmitted at the opposite end and the optical power received at this end is the actual optical power attenuation of the line segment. Compare this value with the line attenuation in the engineering design, if the attenuation is too large, you can refer to the following ideas to locate and troubleshoot.
      • Whether the bending degree of the section of fiber is within the permissible range: bending radius ≥ 60mm, if the bending degree is less than 60mm, re-arming fiber.
      • Whether there are many fiber optic connectors in the section of fiber optic line, and whether the contact is good. If the contact is poor, at the fiber optic connectors, push the connectors tightly into the optical module.
      • Is there any overhead fiber optic cable in this section of fiber optic line that is easily affected by weather. If there is an overhead fiber optic cable, it is recommended that the overhead fiber optic cable be protected from the elements.
      • Is the fiber type and attenuation coefficient of the fiber optic line normal and consistent with the requirements of the engineering design documents. If inconsistent, replace the fiber.
      • Are the fiber optic connectors in this section of the fiber optic line fouled. See Inspection of Fiber Optic Connectors to check for signs of connector fouling and clean the fiber optic connectors promptly.
   3. See if operations are back to normal, if not, turn to other causes.
4. Cause 3: Loose cable connector, no cable connection or wrong cable connection, resulting in business interruption.
   1. Check the cables at the single board interface at this end.

      If ......	then ......
      the cable is loosely connected to the interface.	Tighten the cable. Check if the service is back to normal, if not, continue to the next step.
      The cable is tightly connected to the interface.	Continue to the next step.

   2. Check that the cables are properly connected at the local single board interface.

      If ......	then ......
      the cables are connected incorrectly.	Connect the cables correctly. Check if the service is back to normal, if not, turn to other reasons.
      The cable is connected correctly.	Refer to other causes.

5. Cause 4: Faulty single board laser.
   1. Replace the single board. If the single board supports pluggable optical modules, replace the optical module.
   2. Check whether the single board laser is working properly, if not, turn to other causes.