ASR (Answer-Seizure Ratio) is a key voice-traffic performance metric that measures the percentage of call attempts that are successfully answered.

In simple terms:

ASR tells a VoIP carrier how many attempted calls actually connected to the destination.

ASR is widely used by wholesale VoIP carriers, telecom operators, call centers, CCaaS providers, and voice service providers to evaluate route quality and call performance.

How Is ASR Calculated?

The basic ASR formula is:

ASR = Answered Calls ÷ Total Call Attempts × 100

For example, if a carrier sends 10,000 call attempts and 7,500 calls are answered:

ASR = 7,500 ÷ 10,000 × 100 = 75%

The ASR for that traffic is therefore 75%.

Example of ASR in Wholesale VoIP

Suppose a wholesale carrier sends 100,000 calls to a particular destination.

An ASR of 72% means that 72% of the call attempts were answered according to the carrier’s billing or measurement rules.

The remaining calls may have failed because of busy conditions, no answer, congestion, routing problems, invalid numbers, network errors, or other causes.

What Is a Good ASR?

There is no universal ASR percentage that is considered good for every destination.

ASR can vary significantly depending on:

• Destination country
• Mobile vs. fixed-line traffic
• Calling hours
• Traffic type
• Number quality
• Call-center behavior
• Destination network
• Route quality
• Carrier routing
• Customer dialing patterns

Therefore, carriers should compare ASR against historical performance and comparable routes, rather than using one fixed global benchmark.

Why Is ASR Important for Wholesale Carriers?

ASR helps carriers evaluate whether a route is performing effectively.

A significant decline in ASR can indicate:

• Route degradation
• Destination congestion
• Incorrect routing
• Number-quality problems
• Carrier interconnection issues
• CLI problems
• Traffic-pattern changes
• Blocking or filtering
• Fraud or artificial traffic

For wholesale carriers, monitoring ASR can help identify route problems before they become major customer complaints.

ASR and Route Selection

ASR is particularly important when a carrier has multiple routes to the same destination.

For example:

Route C has the lowest price, but its low ASR may make it commercially unattractive.

This is why sophisticated carriers do not necessarily select routes based solely on the cheapest rate. Cost, ASR, ACD, PDD, CLI performance, capacity, and reliability can all influence routing decisions.

ASR vs. ACD

ASR and ACD measure different aspects of call performance.

ASR measures the percentage of calls that are answered.

ACD (Average Call Duration) measures the average duration of answered calls.

For example:

• ASR: 80%
• ACD: 3 minutes 20 seconds

This means 80% of measured call attempts were answered, while the average answered call lasted approximately 3 minutes and 20 seconds.

Both metrics are useful when evaluating wholesale voice routes.

ASR vs. PDD

ASR measures whether calls are answered.

PDD (Post-Dial Delay) measures the time between initiating a call and receiving the appropriate call-progress response, depending on the measurement methodology.

A route can have:

High ASR + Low PDD = Generally strong call performance

or:

Low ASR + High PDD = Potential route-performance problem

Carriers should therefore analyze these metrics together rather than relying on ASR alone.

Why Can ASR Suddenly Drop?

A sudden ASR decline can have many causes.

Common possibilities include:

1. Route congestion
2. Destination carrier problems
3. Incorrect routing
4. CLI rejection or filtering
5. Invalid or unreachable numbers
6. Changes in customer dialing patterns
7. Network outages
8. Traffic spikes
9. Fraud or abnormal traffic
10. Regulatory or destination-network filtering

When ASR drops, carriers should examine SIP response codes, destination prefixes, time-of-day patterns, CLI behavior, and route-specific performance.

ASR in Call Centers

ASR is also important for call centers and outbound dialing platforms.

A call center may generate thousands of call attempts, but not every number will be answered.

A low ASR can result from:

• Poor-quality contact lists
• Calling inactive numbers
• Aggressive dialing
• Incorrect destination numbers
• Network or carrier issues
• Caller ID reputation problems
• Destination filtering

Therefore, a low ASR does not automatically mean that the underlying VoIP route is poor. Traffic quality and dialing behavior must also be considered.

ASR and Wholesale Route Testing

When testing a new wholesale route, carriers commonly monitor ASR along with other performance indicators.

A practical route evaluation can include:

Rate + ASR + ACD + PDD + CLI + Capacity + Stability

Testing over sufficient traffic volume and different time periods generally provides a more useful picture than evaluating a route from a very small number of calls.

Common ASR Questions

What does ASR stand for in VoIP?

ASR stands for Answer-Seizure Ratio.

What does ASR measure?

ASR measures the percentage of call attempts that are successfully answered.

How is ASR calculated?

ASR = Answered Calls ÷ Call Attempts × 100

Is a higher ASR always better?

Generally, a higher ASR indicates that more calls are being answered, but ASR must be considered alongside traffic type, destination, ACD, PDD, and other route-performance metrics.

Can ASR vary by country?

Yes. ASR can vary significantly between countries and destinations because of differences in network behavior, traffic patterns, dialing practices, and termination conditions.

What is the difference between ASR and ACD?

ASR measures the percentage of calls answered. ACD measures the average duration of answered calls.