Call success rate formula

Which one of the below formula is correct? (Can someone explain the difference?)

  • Call success rate = Call established / Call initiation * 100
  • Call success rate = CSSR - CDR

1st one is Call Setup Success Rate.
2nd one is Call Success Rate.

These are generic formula, so please share counters

CSSR generally incidents RRC SR x Bearere success rate
CDR is Qci1 + Qci5 drop rate in 4G or CS Bearer SR in 3G

I am talking about 2G.