ASR/ACD/SDR

ASR - Answer-Seizure Ratio
The Answer-Seizure Ratio (ASR) is a percentage part of successfully answered Calls from all Calls attempts (successfully answered Calls divided by the total number of Calls attempted and multiplied by 100). The total number of calls attempted, which are known as "seizures". Since busy signals and other rejections by the called number count as call failures, the calculated ASR value can vary depending on user behavior. (http://www.voip-info.org/wiki/view/ASR)

60-70% is considered a very good ASR in the VoIP world.

ACD – Average Call Duration
The Average Call Duration (ACD) is calculated by taking the sum of billable seconds (billsec) of answered calls and dividing it by the number of these answered calls.

In a telecom wholesale or carrier context, SDR = Short Duration Ratio. SDR 6% means that 6% of all completed calls are classified as short-duration calls, according to the carrier's definition (often calls shorter than 6 seconds, though the threshold can vary by carrier).

SDR = N completed​ / (N short < 6 sec) ​​× 100%