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The Measured Sensitivity of the LSX Board May Be Better Than the Nominal Value Because of the Optical Modules on the Board from Different Vendors

Publication Date:  2012-07-25 Views:  54 Downloads:  0
Issue Description
During the engineering test, the difference between the measured sensitivity and the nominal sensitivity of the LSX is large. The nominal received optical power of the optical module on the LSX , which supports 10 km transmission, ranges from �0.5 dBm to �12.5 dBm. The system reports the LOS alarm when the received optical value is �13 dBm. The measured sensitivity of the optical module is �20 dBm. 
Alarm Information
LOS 
Handling Process
1. After a check, it is confirmed that the test is performed properly. That is, the standard test method provided by Huawei is adopted. Details are as follows: The field engineers configure a loopback on the WDM side of the OTU to ensure that the received optical power on the WDM side is normal, attach a test instrument to the client side of the OTU board, install a variable optical attenuator between the client-side optical interface and the test instrument, and then adjust the variable optical attenuator so that no bit error is generated on the test instrument. Then, the engineers adjust the variable optical attenuator so that the optical power decreases until the test instrument receives bit errors. The received optical power measured at this time represents the sensitivity.
2. Test more optical modules on the client side of LSX. It is found that most optical modules have the same problem.
3. Check the threshold for reporting the LOS alarm. It is found that the lower alarm threshold is set to �12.5 dBm.
4. Check the nominal received optical power of this type of optical module. It is found that the value is close to �12.5 dBm. After consulting with R&D, the engineers find that this type of optical module is purchased from multiple vendors. The specifications of such optical modules vary greatly with vendors. The common specifications of all the optical modules from different vendors are thus adopted to demarcate the information of this type of optical module. In addition, Huawei cannot guarantee the good performance of this type of optical module for long time even if the tested index is satisfactory.
5. Replace the modules whose received optical power is close to the sensitivity with the optical module that supports 80 km transmission. 
 
Root Cause
1. The test may be performed improperly.
2. The nominal received optical power value of the optical module may be improper.
3. The software setting may be incorrect. 
 
Suggestions
It is recommended that the network be planned and projects be implemented according to nominal values.  

END