Answer-seizure ratio (ASR)

ASR, the answer-seizure ratio, is the share of call attempts that were answered. It is the first number to look at when you judge a customer’s traffic or a vendor’s quality. A low ASR means many attempts that load the switch and the vendors but bring no revenue, because only answered calls are billed.

How it works

ASR is calculated as answered calls divided by all attempts, times 100:

ASR, % = answered calls / call attempts × 100

An attempt is every call that reached the switch or the vendor, answered or not. An answered call is one with a non-zero duration, whether a person or a voicemail system picked it up. ASR is always read together with ACD, the average duration of the answered calls: high ASR with very short ACD often means calls answered by machines or dropped at once.

FlySIP calculates ASR in two places:

ASR/ACD Reports. Reports → ASR/ACD Reports shows ASR, ACD and PDD for a period. The Origination table counts calls per caller, IP or CLI. The Termination table counts attempts per vendor or connection. See Reports.
Quality monitoring. Each monitored connection tracks its ASR over the last calls and is demoted or blocked when it drops below ASR Threshold, %. See Quality-based routing.

The two sides differ. A call that hunts through three vendors before one answers is one attempt and one answered call for the caller, but three attempts and one answer on the vendor side. Vendor ASR is therefore always lower than the ASR of the traffic you receive, and the more failover your routing does, the larger the gap.

Key terms

ASR — answer-seizure ratio: percentage of attempted calls that were answered.
ACD — average call duration of answered calls.
PDD — post-dial delay: time between sending INVITE and receiving ringing.
Hunting — trying the next route after a failed attempt.
Origination — receiving calls from a network into the switch, e.g. on DIDs.
Termination — delivering a call to its destination network through a vendor.

Common scenarios

Retail and national traffic

Calls made by people to people have a high ASR, often around 70%, and long ACD. ASR drops temporarily at peak times such as holidays, when networks and lines are busy. National carriers often require at least 50 to 60% from wholesale partners before they interconnect.

International wholesale

Wholesale carriers move traffic across several vendors at the lowest cost, and calls fail over from one vendor to the next. An ASR of about 50% is a common target; more is needed to get the best rates from national carriers. Carriers that mix in call-centre traffic limit its share with Max Calls Per Second and Max Sessions, because it pulls their average down.

Call centres and autodialers

Autodialers dial many numbers for every free agent and pass only answered calls on. Many numbers are wrong or badly formatted, and attempts arrive at a high rate. ASR is usually below 20% and ACD is short. Price such traffic accordingly, limit its CPS, and do not apply quality thresholds tuned for retail traffic to the connections that carry it. See Understanding CPS.