Check my reply on the topic”Abrupt nature of SDCCH Blocking in N/W”.
This ratio is set in BSC .The parameter name is “ALSDC”.The recommended value is 30%.
To handle this alarm,you can check the following
1.If any TRX containing SDCCH has gone faulty or blocked.
2.If the parameter ALSDC is set too high.
3.Wheteher Dynamic SDCCH is disabled