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.

Hi Experts,
Anyone familiar with ITU/ETSI formula of mobile-call unsuccessful rate?

They have clarified that its the unsucc calls to the total call att.
The call att should be to a legit number that is in a coverage area.
Within 40 seconds from the instant where last digit of the called number is received by the network.
And should it be weighted by the proportion of calls per technology or is it a simple average.