This topic describes how to troubleshoot the fault of ONU frequent going online and offline.
Fault Description
Network topology: Optical split level: one level; split ratio: 1:32; backbone fiber: 8.6 km long; branch fiber: 1.5 km long. In an office, an ONU frequently goes online and offline.
Alarm Information
LOSi alarm and LOFi alarm
Possible Cause
l The ONU receive optical power is larger than the overload optical power.
l The ONU receive optical power is smaller than the sensitivity.
l There is abnormal attenuation on ODN lines.
Procedure
Step 1 Test the receive optical power on ONU optical ports. It is found that the receive optical power is only -28 dBm. This indicates that there is abnormal attenuation on ODN lines.
Step 2 Check field conditions. It is found that fibers are placed disorderly, the fiber bend radius is too small and the fiber is almost broken, as shown in Figure 1.
Figure 1 Too small fiber bend radius
Step 3 Replace the fiber and test the ONU receive optical power again. -18 dBm optical power is obtained and services recover. This indicates that the too small fiber bend radius causes abnormal attenuation on ODN lines and consequently causes the ONU to go online and offline frequently.
Step 4 Such a fault does not recur in the next week.
—-End
Suggestion and Conclusion
Make sure that the fiber bend diameter is larger than 8 cm when bending a fiber.
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