Two most widely used metrics for indicating VoIP route quality are the answer-seizure ratio (ASR) and average call duration (ACD). You need to understand and fully utilize them in your business when selecting the best routes from your providers, forecasting call volumes, determining traffic demand, measuring the performance of your infrastructure and fixing things when call quality deteriorates.
What is Answer-Seizure Ratio (ASR)?
ASR is the percentage of successfully connected calls to the total number of attempted calls.
ASR % = (total number of answered calls / total number of calls) × 100
For example, if there were 100 calls dialed of which 60 were successfully connected, then:
ASR (%) = (60 [successful calls] / 100 [dialed calls]) x 100 = 60%
ASR should be at least 40–50%, and above 60% would indicate an excellent quality service. A high ASR indicates a reliable network, since most calls that are attempted are answered.
What is Average Call Duration (ACD)?
ACD is the average length of an answered call made over the network.
ACD = duration of all answered calls / number of answered calls
For example, if there were 60 answered calls with a total duration of 120 minutes, then:
ACD = 120 [duration of all answered calls] / 60 [total number of answered calls] = 2 minutes
An ACD of 4–5 minutes is considered okay, whereas anything above 6 minutes is excellent. A high ACD suggests that few calls are dropped or abandoned due to quality issues.
Bad ASR and ACD
There are many factors which may lead to a low ASR and ACD and thus lowering the network quality.
The following factors may result in low ASR:
  • User behavior
  • Busy destination lines
  • Far-end switch congestion (capacity problems at the carrier
There are many factors can reduce call quality to give a low ACD:
  • Congestion
  • Long PDD (Post Dial Delay)
  • Looping
  • FAS (False Answer Supervision – dead air)
  • Echo
  • Jitter (variance in delay)
  • Delay (delays of more than 300 ms decrease ACD)
  • Packet loss
  • Low-quality codecs
  • The capacity (measured in packets per second or PPS) of an Ethernet network can be a bottleneck
  • Too many hops (Session Border Controller passing media through them) will also decrease ACD
  • Traffic profiles can also contribute toward a low ACD
How to improve ACR and ACD?
Call Definition
Since it is sometimes unclear what constitutes a phone call (does a phone call include automated messaging or only when an agent engages a customer?) it is important to benchmark your ACR and ACD metrics with companies that have a similar definition of a phone call as yourself. Other companies within your industry will typically have similar definitions, but not always.
Call Volume
The amount of phone traffic your team receives plays a major role in the ACR and ACD. The more traffic, the more emphasis a company should put on engaging as many customers as possible, as opposed to increasing an individual customer’s call connection and call length. This trade-off is the reason that benchmarking against companies with similar volume of calls will give your team a better estimate as to the optimal length of call.
At Denovo Labs, we always maintain a high ASR and ACD rate so that our network quality remains superior.
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