Hello, everyone!
Today I'd like to share a case with you!
Problem Description
Between 1:00-2:00 a.m. on July 20, 2020, A 100G ASON (Electrical Layer) service from A site to D site was interrupted for about 10 minutes.
Problem Analysis
Service Information:
Source NE | Sink NE | Rate |
A | D | ODU4 |
Step1: Analyzing NE data, historical alarms, rerouting records on July 20.
a) Analyzing historical alarms. The SUM_INPWR_LOW alarm reported on C site at 1:20 July 20,then the service signal degrades.
b) Analyzing rerouting records. The service has only two rerouting records when bit errors occur.
c) Check ASON service configurations and found Rerouting Triggered by SD function was disabled. This means that the trails are not rerouted when the BE didn’t trigger the SF alarm.
EventType | Alarms That Trigger Rerouting |
SF | The trigger conditions of electrical-layer service rerouting include the following alarms: ODUk_PM_AIS, ODUk_PM_OCI, ODUk_PM_LCK, ODUk_PM_SSF, ODUk_LOFLOM, ODUk_AIS, ODUk_LCK, ODUk_OCI, ODUk_TCM_LCK, ODUk_TCM_AIS, ODUk_TCM_OCI, ODUk_TCM_TIM(Enable TIM response), ODUk_TCM_LTC OTUk_AIS, OTUk_LOF, OTUk_LOM, R_LOS |
SD | The trigger conditions of electrical-layer service rerouting include the following electrical-layer service alarms: ODUk_PM_DEG, ODUk_PM_EXC OTUk_DEG, OTUk_EXC, ODUk_TCM_EXC, ODUk_TCM_DEG |
Based on the preceding analysis:
Fiber fault occurs at 1:20 on B-C section.
OTU4_LOF alarm was reported on the trail and triggering rerouting, but signal degradation still exists.
At 01:28, the OUT4_LOFLOM alarm was reported and rerouting was triggered again. Then, the service was restored.
Between 1:20 and 1:28, the Rerouting Triggered by SD function was not enabled. As a result, rerouting was not triggered for the service during this period, Therefore, bit errors persisted for nearly 9 minutes.
Root Cause
1. The received optical power at C site-12-13OAU1-1(IN) was unstable due to fiber fault. As a result, bit errors were generated.
2. The Rerouting Triggered by SD function was disabled for the ASON trail and the DEG alarm does not trigger rerouting. During this period, bit errors always exist.
Solution
Check and repair the optical cables on the trail. Avoiding high optical cable attenuation.
Enable The Rerouting Triggered by SD function for all ASON services. The procedure is as follows:
Right-click the ASON trail---Set Routing Properties---Rerouting Triggered by SD---Yes---Apply.
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