Situation A.—> The Customer is calling and the calls are not getting connected due to network busy he keeps on calling the same number. Say he tried the same number 10 times he got himself connected to the destination once and call was answered now let us understand what CSSR formula says about this situation,
Call Setup Success Rate= No.of times the call Connected Y = 1
Total No. of Attempts X 10
Which means the CSSR is now 0.1, here the ASR may be 0.1 (if the call is answered) will be 0 if the call is not answered.
Here One more point to remember the ASR can only be lesser or equal to CSSR.
Formula for Calculation of ASR:-
Answer to Seizure Ratio= No. of Answered calls
No. of times the Circuits Seized
The question that may be asked here is Why are we considering the number of times Circuit Seized why not attempts, the attempt is not considered in this formula because as per the customer point of view the attempt is counted when he called and the call dropped or somehow call never reached the switch and disconnected.
The calculations based on number of attempts never give right picture of core performance hence the circuit seizure is counted for calculation because a circuit is seizes only when call reaches the switch and switch has performed Location, Authentication, Balance and Validity and receive routing information from HLR along with TLDN(Temporary Local Directory Number) hence routed call to the destination switch with its point code and allocated a Traffic channel for the call.
When we take in to account the circuit seizure it ensures that NSS Performance is properly adjudged with this however for the calculation of performance of RAN and BSS attempts are taken into consideration. Both ASR (Basically for RAN and BSS Performance Monitoring) and CSSR (Basically for NSS Performance Monitoring) are required to properly understand the proper utilization of all nodes and fix any issues if any.