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MSP Ring Switching Is Abnormal Because B3_EXC Threshold Is Set to a Low Value

Publication Date:  2019-07-04 Views:  130 Downloads:  0

Issue Description

Six sets of OptiX OSN 3500 that are configured with the N2SL64 boards form a 10 Gbit/s MSP ring. During the MSP ring switching test, the fiber is cut. The services, however, are not interrupted and the MSP switching is normal. Reconnect the fiber. The switching is restored after 10 minutes. The services, however, are interrupted immediately and are automatically restored in four minutes. At the same time, the optical board where switching is performed reports the B3_SD alarm. The B3_SD alarm lasts for two hours and then is automatically cleared. Check on the T2000. It is found that the MSP switching is normal. Replace the XSC board. It is found that the fault persists. 


Alarm Information


Handling Process

Modify the B3_EXC and B3_SD thresholds to the default values. Then, the problem is solved.  

Root Cause

 The problem occurs because the B3_EXC and B3_SD thresholds are lowered for the N2SL64 board on the entire network. As specified in G.806, the EXC threshold is 1.0E-x (x = 3, 4, or 5) and the SD threshold is 1.0E-x (x = 5, 6, 7, 8, or 9). Currently, the EXC threshold is defaulted to 1.0E-3 and the SD threshold is defaulted to 1.0E-6 for the OptiX OSN 3500. If the B3_EXC and B3_SD thresholds are lowered to 1.0E-8 and 1.0E-9 respectively, bit errors occur during the MSP ring switching. When the bit errors exceed the B3_EXC and B3_SD thresholds, the alarms are generated.

As specified in G.806, when the bit error rate (BER) is 1.0E-8, the alarm clearing time is 1000s, and when the bit error rate (BER) is 1.0E-9, the alarm clearing time is 10000s. Hence, when the B3_EXC threshold is set to 1.0E-8, the alarm generally lasts for about 15 minutes and then is cleared even if the condition for triggering the B3_EXC alarm already disappears. Currently, the AU_AIS is inserted by default, when the B3_EXC is generated for the OptiX OSN equipment. As a result, the services are interrupted after the MSP switching. When the B3_SD threshold is set to 1.0E-9, generally the alarm lasts for more than two hours and then is cleared. During the previous switching test, the services are restored about 15 minutes (that is, the WTR time of 10 minutes plus service interruption of four minutes plus the time for reconnecting the fiber) after the switching. 



 It is recommended that you disable the AU_AIS insertion in the case of B3_EXC alarm.