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Some BTSs reset when XPU boards are switched over

Publication Date:  2018-04-11 Views:  112 Downloads:  0
Issue Description
The BTS version is V901R008C01 or later at a site. On April 17, 2014, the following boards were switched over during the operation time: OMUs, XPUs, SCUs, TNUs, PEUs, and EIUs. When the XPUs were switched over, a total of 107 BTSs reset on April 17. Board switchover is performed during the operation time, and there is no impact on ongoing services. All BTSs that reset started and worked properly. 
Handling Process
A mirror test is conducted in the lab based on onsite logs and the problem symptom. The test result shows that some BTSs reset after XPUs are switched over multiple times.

BSC commissioning methods are then used in the lab to print BTS data on the standby XPU. Comparison of the BTS data indicates the following information:
Data blocks for BTSs that do not reset

Data blocks for BTSs that reset

In the data blocks of the BTSs that reset, the backup flag for the standby board is 0 instead of 43947 (0xABAB). The flag 0 indicates that backup fails, and the flag 43947 indicates that backup succeeds. In this situation, the BTS with a backup failure needs to reset for initialization.

Then, BSC experts responsible for different fields are coordinated to check and troubleshoot the backup mechanism and code. The check result shows that the code for a processing procedure has defects, which may cause a backup failure. As a result, some BTSs reset.

The backup mechanism is then optimized in the lab, and the BSC of a debug version is used for tests. The tests show that the problem has been resolved, and problem locating is complete.
When the BSC is working properly, the standby XPU synchronizes BTS data from the active XPU. Due to the BSC code defects, data backup may fail. In this situation, if the active and standby XPUs are switched over, the BTS experiencing a data backup failure will be initialized because of the data synchronization failure in the standby XPU. As a result, the BTS resets. If the BSC is working properly and XPUs are not switched over, this problem has no impact. The BSC of a version where this problem is resolved was released in June 2014.