All of a sudden we started to have degradation in Inter BSS Handover Success Rate for 3 BSCs(ALU) of a city.Note that Intra BSC HO Success Rate is totally fine and problem is only for the bordering cells of these BSCs which are having high percentage of ROC now. Also, the Core is a pool MSC which contains 8 BSCs of this city whereas the problem is only observed in 3 BSCs. Still we escalated the issue to Core but no problem found. Similarly on doing the audit on Cell/BSC level, no discrepancy or change observed that could have led to this degradation. On doing the Drive Test, it is found that all Failures are of the b/m cause:
“Value : (111) Protocol error, unspecified”. Also, the time difference btw HO Cmd and HO Failure is very small. We get HO Cmd, followed by HO Access(sent by MS) and HO Failure and all these messages come within a second.
I have done the delete/recreate of problematic HO Relations, SUMA Reset and lastly just changed the Clock Synchronization mode from PCM Synch to Free Running(just as a trial). The effect of this last action is still under observation. Do you have any clue that what could be the reason behind this degradation?