Thanks PIX and TNS for the response
Now in my scenario (GHOST / PHANTOM RACH) following points has been observed.
1. The Location Update attempt do not go to the MSC but is discarded before BSC sends it to MSC. Discarded in BSC with Timers expire. At NSS end LU success rate is fine and around 96 %.
2. No SD blocking is observed.
3. Particular area gets affected and all of its cells covering that area have this issue.
4. The issue is always LU failure thus effecting CSSR. LU failure goes to around 80-85 % of all those cells.
5. Mostly the issue raises at night at around 3-4 am
6. Cells are not any LA border cells.
7. There are around 400-500 attempts and 85 % failures and the attempt and failures scenario goes for around 3-4 hours. sometimes also goes for 6 hours.
8. MOC / MTC / SMS SDCCH attempts are OK and success rate is around 95-97 %
Again what confuses me that “No SD blocking is observed”
and all LU failures are due to timer expiry