Hello, everyone!
Today, I'd like to share a case with you.
Fault Description
Two fiber cuts occur in the ultra-long span transmission (attenuation in the span is greater than 44 dB). That is, the optical cable between station Legasp and station CAL, and the optical cable between station TAC and station CAL are broken at the same time. Lasers on the HBA and RPC boards are automatically shut down and station CAL is unreachable to the NMS. After the optical cables are restored, the laser on the RPC board cannot be automatically started.
Possible Causes
The possible causes are as follows:
The span does not contain any one of wavelengths numbered 74, 76, 78, and 80. The PIN on a CRPC board can detect only wavelengths numbered 74, 76, 78, and 80. Therefore, a system configured with IPA pairs must carry at least one of the mentioned wavelengths. In a system configured with the ASON function, the CRPC board may not detect any optical power if the four wavelengths are rerouted to other paths.
The alarm detection threshold for the OA board is set incorrectly. Check whether the alarm detection threshold for the OA board is set correctly by referring to Detection Board Threshold (dBm) (for a System Using Only Backward CRPC Boards) in section 2.1.1 "Principles for Setting Parameters."
No auxiliary detection board is configured. To improve the accuracy of determining a fiber cut, you need to configure auxiliary detection boards in a system configured with CRPC boards. In addition, you need to set the OSC board as an auxiliary detection board and you can choose whether to set the OTU or CRPC board as an auxiliary detection board.
The NE is unreachable to the NMS.It is found that no SC2 board is configured at station CAL and the system adopts ESC communication. The NE is unreachable to the NMS when the optical cable is broken. When the optical cable is restored, the IPA function cannot be restarted and therefore the laser on the RPC board cannot be started. If the NE is reachable, start the lasers on the CRPC boards at two ends of the IPA pa*****d then restart the IPA function. In this case, alarms on the OTU board can be cleared and the IPA function can be restarted.
Procedure
Cause 1: The span does not contain any one of wavelengths numbered 74, 76, 78, and 80.It is found that the system contains the mentioned wavelengths and is not configured with the ASON function.
Cause 2: The alarm detection threshold for the OA board is set incorrectly.
Step 1 Measure the actual receive optical power of the detection board and compare the result with the value of Detection Board Threshold (dBm)
Step 2 If the actual receive optical power is lower than the value of Detection Board Threshold (dBm), recalculate and change the value of Detection Board Threshold (dBm). Ensure that the value is smaller than the actual receive optical power.For details on how to calculate the value of Detection Board Threshold (dBm), see section 2.1.1 "Principles for Setting Parameters."
Cause 3: No auxiliary detection board is configured.In this example, the transmission span is ultra long. In this case, the laser on the CRPC board is not started when the IPA function is restarted. Consequently, the input optical power of the OTU board is very low and the OTU board reports the LOS alarm. This indicates that the system determines that the optical cable is not restored by default. Therefore, the OTU board cannot be set as an auxiliary detection board in this example.
It is found that no OSC board is configured in the system. It is recommended to configure the HSC1 board and set the board as an auxiliary detection board. The maximum output optical power and the receiver sensitivity of the HSC1 board are +10 dBm and –48 dBm respectively.
If the HSC1 board is configured, the FIU board must be configured.
Cause 4: The NE is unreachable to the NMS.
It is found that no SC2 board is configured at station CAL. The NE is unreachable to the NMS when the optical cable is broken. When the optical cable is restored, the IPA function cannot be restarted and therefore the laser on the RPC board cannot be started.
----End
Thanks！
