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ODUK-SNCP Switching Fails in the Case of the Inconsistency Between the Physical and Logical Fiber Connections

Publication Date:  2012-08-12 Views:  417 Downloads:  0
Issue Description
In a deployment project of the OptiX OSN 6800 equipment, the ODU1-SNCP protection service is configured to protect the lower-layer services. 
  

622 Mbit/s SNCP services are configured between the TOM board at node C and the TOM board at node J. Node C receives the services from nodes D and B and is configured with the SNC-N protection service. One day, the physical fiber between nodes B and C is broken, both the active and standby NS2 boards of the protection group are in the SF state, and the services are interrupted. After being forcibly switched to the working channel, the services are restored. 
 
Alarm Information
RLOS 
Handling Process
1. Query the SNCP switching mode. The query result shows that the SNCP switching mode is the non-revertive mode. As a result, the services are operating in the standby channel before the fault occurs.
2. Check whether the logical fiber connections are inconsistent with the physical fiber connections. Query the logical fiber connections. The logical fiber connections queried are as follows:
The logical fiber connections at node C are as follows (for information about the query command, see the attachment at the bottom of this table):
Working channel: FIU in slot 15 -> VA in slot 14 -> OAU in slot 9 -> ITL in slot 13 -> D40 in slot 5 -> NS2 in slot 101
Protection channel: FIU in slot 215 -> OBU in slot 208 -> OAU in slot 210 -> ITL in slot 213 -> D40 in slot 205 -> NS2 in slot 102
3. Check the physical fiber connections on site. The physical fiber connections are as follows:
D40 in slot 5 -> NS2 in slot 102
D40 in slot 205 -> NS2 in slot 101
4. In the OptiX OSN 6800 V100R004, if the upstream multiplexing board reports the MUT_LOS alarm, the NE software sets the OTU board in the downstream to the SF state.
5. In case of a fiber break, the FIU in slot 15, OAU in slot 9, ITL in slot 13, and D40 in slot 5 report the MUT_LOS alarms at the same time when the NS2 in slot 102 reports the alarm. Therefore, the NE software sets the protection switching state of the OTU board in the downstream to SF. In this case, the actual services are not affected. The actual input optical power of the preceding multiplexing board is �600 dBm but the input optical power of the NS2 in slot 101 is about �160 dBm and the multiplexing board in the protection channel does not report alarms. The most possible reason is that the logical fiber connections configured for the NS2 in slot 102 and NS2 in slot 101 reverse the respective physical fiber connections. That is, the correct logical fiber connections should be D40 in slot 5 -> NS2 in slot 102 and D40 in slot 205 -> NS2 in slot 101, which reverse the physical fiber connections as shown in the preceding figure.
6. Because the logical fiber connections reverse the respective physical fiber connections, the NS2 in slot 101 is mistakenly set to the SF state. As a result, SNCP protection switching is not triggered automatically, and the services are recovered only after a forced SNCP switching is performed. 
 
Root Cause
Both the active and standby NS2 boards of the protection group are in the SF state, and the SNCP switching is abnormal.  
Suggestions
Ensure that the physical fiber connections are consistent with the logical fiber connections in the OptiX OSN 6800. 

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