Fault Description
Network topology: Originally, the system uses one-level optical split and the split ratio is 1:8. Later, the customer connects a 1:16 optical splitter to the 1:8 optical splitter. The three ONUs are connected to the 1:16 optical splitter.
During deployment in an office, three ONUs frequently go online and offline.
Alarm Information
None
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 ONU receive optical power. It is found that the receive optical power of the three ONUs is approaching the sensitivity.
Step 2 Analyze the total split ratio of the three ONUs. It is found that the total split ratio is 1: (16 x 8) = 1:128, which is too large and therefore causing too large attenuation, as shown in Figure 1.
Figure 1 Too large split ratio
Step 3 Change the 1:16 optical splitter to a 1:4 one. Then, the fault is rectified.
Step 4 Such a fault does not recur in the next week.
—-End
Suggestion and Conclusion
Bit errors will occur on an ONU if the ONU receive optical power is approaching the sensitivity and even the ONU may go offline. Reserve a 3 dBm attenuation margin in ODN planning.
NOTE
The specifications of the optical path attenuation are as follows (the following are theoretical values and the actual values vary with the environment):
l The optical attenuation on the ONU GPON port should be within the range of 15 dBm to 25 dBm.
l The attenuation on an optical fiber is about 0.3 dB per kilometer.
l The attenuation for an optical splitter is as follows:
l 1:2 optical splitter: 3 dBm
l 1:4 optical splitter: 6 dBm
l 1:8 optical splitter: 9 dBm
l 1:16 optical splitter: 12 dBm
l 1:32 optical splitter: 15 dBm
l 1:64 optical splitter: 18 dBm
5 ONU Frequently Goes Online and Offline(1) – a Rogue ONU
SmartAX MA5600T/MA5603T Multi-service Access Module Troubleshooting: ONU Frequently Goes Online and Offline: TC-C6217 ONU Frequent Going Online and Offline Caused by a RogueONU.
This topic describes how to troubleshoot the fault of ONU frequent going online and offline.
Fault Description
All ONUs connected to a port in an office frequently go online and offline after a flood.
Alarm Information
Rogue ONU 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 After communicating with the customer, we learn that there was once a flood some ONUs are flooded.
Step 2 Analyze the condition. Only certain ONUs are flooded. This should not cause all ONUs to go offline repeatedly. It is concluded that the optical modules of certain ONUs transmit signals abnormally because of flood and the ONUs become rogue ONUs.
Step 3 Check optical lines one by one near the optical splitter. It is found that one ONU works in the continuous mode, as shown in Figure 2.
Step 4 Replace the ONU. System services recover.
Step 5 Such a fault does not recur in the next week.
—-End
Suggestion and Conclusion
In normal conditions, ONU signal transmit timeslots are controlled by the OLT. A rogue ONU is an ONU that goes out of control of the OLT and works in the continuous mode or irregular mode. You can locate a rogue ONU manually or locate a rogue ONU by querying alarms generated on the OLT. If a rogue ONU is detected, replace it in time.
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