It is recommended to calculate CSSR from Drive Test. Although for Ericsson systems the recommended CSSR formula is
CSSR = 100 * ([TCASSALL + TFCASSALLSUB + THCASSALL + THCASSALLSUB]/ TASSALL) * (1 – ([RAOREQ + RAAPAG + RACALRE]/CNROCNT) * (CCALLS-CMSESTAB)/CCALLS) * (1 – ([RAOREQ + RAAPAG + RACALRE]/CNROCNT)* (CNDROP – CNRELCONG)/CMSESTAB)
Hence it can be explained as
CSSR = TCH Assignment * (1-SD Establishment for TCH Calls) * (1-SD Drops for TCH Calls)