The wavelength wander of an OTU board causes the downstream OTU boards to report the IN_PWR_LOW alarm.
Symptom
The OptiX BWS 1600G is networked in the chain mode: OTM----OTM (A)----OTM (B) ----OTM, that is, multiple OTM stations form a ring of 7 channels (one is standby). One day, the IN interface of the 18th-channel LWC board at station B reports the IN_PWR_LOW alarm.
Cause Analysis
- The LWC board of station B is faulty or a fault in the fiber from the D40 to LWC causes excessively high attenuation.
- The launched optical power of the opposite station A is abnormal. As a result, the local received optical power is abnormal.
- Other boards are faulty, for example, the M40 at the transmit end or the D40 at the receive end is faulty. Because these two boards are passive optical components, they are less likely to be faulty.
- Other causes.
Check the optical power of the equipment level by level from the downstream to the upstream according to the signal flow for fault locating.
Procedure
- Measure the input optical power of the D40 and LWC at station B. Excessively low optical power causes the OTU board to report the alarm.
- Scan the wavelengths of the D40 and OAU at station B with a multi-wavelength meter. The 18th wavelength is absent.
- The wavelength ranges of the LWC and M40 at station A are in consistent. The 18th wavelength is not input to the M40. Measure optical interface 23 of the M40 at station A. The input optical power is measured as -2 dBm (normal).
- Scan the wavelengths of the M40 board at station A. The 18th wavelength is still absent. Use the optical power meter to measure the optical power, which is found normal.
- Directly scan the wavelengths of the OUT interface of the 18th-wavelength LWC board. The root cause of the fault is finally located. The scanning result shows that the optical power of the 18th wavelength is -2 dBm (normal value) and the wavelength is 1547.468 nm. The standard wavelength, however, is 1546.92 nm. The wavelength wander is up to 0.5 nm. In the WDM system, the wavelength wander range of the OTU board should be not more than 0.15 nm.
- Temporarily solve the problem by using the standby wavelength between the two stations. Apply for a new 18th-wavelength LWC board and replace the faulty LWC board.
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