Hello,
There will be SD drop in case of TCH congestion.
here is the formula you can calculate SD drop Without TCH congesiton :
=(SDCCH_RADIO_FAIL+SDCCH_RF_OLD_HO+SDDCH_LAPD_FAIL+SDCCH_BTS_FAIL+SDCCH_USER_ACT+SDCCH_BCSU_RESET+SDCCH_NETWORK_ACT+SDCCH_ABIS_FAIL_CALL+SDCCH_ABIS_FAIL_CALL_OLD+SDCCH_A_IF_FAIL_OLD)
/ (SDCCH_HO_SEIZ+SDCCH_ASSIGN)