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Protection Switching on an OptiX OSN 9500 Causes Transient Alarm Reporting on NE80E

Publication Date:  2013-10-08 Views:  41 Downloads:  0
Issue Description
On a transmission national backbone network of an operator, two OptiX OSN 9500s formed a cross-province 1+1 linear MSP protection group. A 2.5 Gbit/s optical ports on the client side of OptiX OSN 9500 was interconnected with the POS port on NE80E. One day, the customer reported transient interruption on the POS port of NE80E.  Checked and found that the POS port received P_AIS and P_RDI alarms upon the transient interruption and the port was set to LINK_DOWN.
The POS port on NE80E received transmission alarms:

>>%Mar 27 02:14:04 2007 GXNN-BC-SXNET-RT01-NE80E PHY/2/PHY:Slot=6;    POS6/0/0: change status to down  PAIS PAISI
>>%Mar 27 02:03:18 2007 GXNN-BC-SXNET-RT01-NE80E PHY/2/PHY:Slot=6;    POS6/0/0: change status to down  PRDI PRDII
>>
>>%Mar 27 01:01:09 2007 GXNN-BC-SXNET-RT01-NE80E PHY/2/PHY:Slot=6;    POS6/0/0: change status to down  PAIS PAISI
At the same time, the port status changed to LINK_DOWN.
Handling Process
Analyzed the OSN 9500 and NE80E for fault causes and found that:
1. OptiX OSN 9500 side: The SDH network carrying data services from NE80E used 1+1 linear MSP networking. 1+1 linear MSP switching principle: At the active route interruption moment, the signal on the active route failed. Upon detection of an SF, the OptiX OSN 9500 triggered switching; after the switching, services were carried on the standby route and were restored (as specified in ITU-T, the signal failure time was within 50 ms). All actions on the OptiX OSN 9500 were expected reactions during a normal protection switching.
2. NE80E side: NE80E was connected to OptiX OSN 9500 through its POS port. The external port signal on the POS port was an SDH standard signal. Therefore, when protection switching occurred on the OptiX OSN 9500, NE80E would detect a short-time path signal failure (P_AIS). When the POS port on NE80E received the local receive signal failure, its status changed to LINK_DOWN and reported the corresponding alarms. After switching on OptiX OSN 9500 was complete, services were restored, the status of the POS port on NE80E recovered to LINK_UP and reported corresponding alarms notifying of the status recovery.
To sum up, when the active route on the OptiX OSN 9500 side was interrupted and protection switching occurred, it was normal that corresponding alarms were reported on the NE80E side. The service interruption time on the OptiX OSN 9500 was within 50 ms and the LINK_DOWN time of the POS port on NE80E was also within 50 ms, which did not significantly affect services.
Root Cause
When a switchover occurred on the OptiX OSN 9500, NE80E would detect an exception and triggered switching.
Solution
When services from datacom devices need to be transmitted by transport devices, the datacom devices and the transport devices are interconnected through SDH ports, and the transport devices are configured with protection, it is recommended that you set a hold-off time of 50 ms when the ports on the datacom devices are LINK_DOWN to prevent simultaneous switching on the transport and datacom devices. 
Suggestions
When services from datacom devices need to be transmitted by transport devices, the datacom devices and the transport devices are interconnected through SDH ports, and the transport devices are configured with protection, it is recommended that you set a hold-off time of 50 ms when the ports on the datacom devices are LINK_DOWN to prevent simultaneous switching on the transport and datacom devices. 

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