 This topic describes how to troubleshoot the fault when the ONUs under the same PON port frequently fail to be recovered. Fault Type Quality of the optical path Fault Description 18 ONUs are connected to a GPON port of the GPBC board through a 1:32 optical splitter on the MA5600T. More than 10 ONUs (including MA5616 and MA5620E) are in the configuring state, but they fail to be recovered. A certain ONU can be recovered after a while, but turn to configuring state again, affecting the service. Alarm Information Loss of ONT optical signal, loss of GEM channel, the optical module fails to transmit signals (fails to deliver TF) Cause Analysis - The attenuation of the optical signals received by ONU is excessively large.
- The optical signals on the PON port are interfered.
- The optical module is faulty.
Procedure - This fault occurs on more than ten ONUs, which indicates that the fault is not caused by the hardware of ONUs.
- Run the undo ont ipconfig command on one of the faulty ONUs to clear the IP information. Then run the snmp-profile delete command to disable the SNMP management profile and run the ont activate command to reactivate the ONU. Run the display ont info command to query the Config state. The failed is displayed.
- Evaluate the optical power range on the ONU: The mean launched power of the PON port is about 3 dBm. The attenuation of the optical splitter is about 17 dBm. The insertion loss of the optical fiber is about 1 dBm. Therefore, the optical power on the ONU is calculated as follows: 3 - 17 - 1 = -15 dBm. Measure the optical power on the fiber patch cord of one faulty ONU. The receive optical power is -16.5 dBm, which is within the normal range.
- Check whether non-PON optical signal is transmitted to the optical splitter. No such signals are found.
- Check the historical alarms. It is found that the LOS alarm is generated on the No.12 ONU most frequently, and the optical path of NO.12 ONU is of poor quality but this problem has not been resolved. Measure the onsite ONU receive optical power of No.12 ONU. It is -34 dBm. However, the optical power of other ONUs is about -16 dBm, which is 18 dBm different from that of NO.12 ONU. Normally, the difference between the maximum optical attenuation and minimum optical attenuation of ONUs connected to the same PON port should be within 15 dBm. Improve the optical path quality of No.12 ONU. Then all the ONUs recover to normal state.
Suggestion and Summary - The difference between the maximum optical attenuation and minimum optical attenuation of the OLT optical receiver is within 15 dBm. If the difference exceeds the range, the bit error rate (BER) will increase or some ONUs go offline.
- The faulty ONU or ONU optical path must be handled timely. Otherwise, other ONUs on the same PON port will be affected.
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