ACD (Average Call Duration) is a key telecommunications metric that measures the average length of answered calls over a specific period.

In simple terms:

ACD tells a carrier how long, on average, answered calls remain connected.

ACD is commonly used by wholesale VoIP carriers, telecom operators, call centers, CCaaS providers, and voice service providers to evaluate traffic patterns and route performance.

How Is ACD Calculated?

The basic formula is:

ACD = Total Duration of Answered Calls ÷ Number of Answered Calls

For example, if 1,000 answered calls generate a total of 300,000 seconds of conversation time:

ACD = 300,000 ÷ 1,000 = 300 seconds

Therefore:

ACD = 5 minutes

The average answered call lasted approximately five minutes.

Why Is ACD Important in Wholesale VoIP?

ACD provides useful information about the nature and quality of voice traffic.

A route with a very low ACD may indicate:

• Calls are being answered but quickly disconnected
• Poor call quality
• Incorrect routing
• Traffic with short-duration calling patterns
• Unwanted or artificial traffic
• Call-center dialing behavior
• Destination-specific call characteristics

However, low ACD does not automatically mean a route is bad. Some legitimate traffic naturally produces short calls.

For example, appointment reminders, delivery calls, verification calls, and some call-center campaigns may have relatively short durations.

Example of ACD in Wholesale Voice

Suppose a carrier has the following traffic:

The ACD is:

1,400,000 ÷ 7,000 = 200 seconds

Therefore:

ACD = 3 minutes 20 seconds

This tells the carrier that the average answered call lasted approximately 3 minutes and 20 seconds.

ACD vs. ASR

ACD and ASR measure different things.

ASR (Answer-Seizure Ratio) measures the percentage of call attempts that are answered.

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

For example:

ASR: 75%
ACD: 4 minutes

This means 75% of measured call attempts were answered, and the average answered call lasted four minutes.

Looking at both metrics together provides more useful information than looking at either metric alone.

ACD vs. PDD

PDD (Post-Dial Delay) measures how long it takes for call setup to progress after the call is initiated, according to the measurement methodology being used.

ACD measures what happens after the call is answered.

Therefore:

• PDD → Call setup performance
• ASR → Call answer performance
• ACD → Answered-call duration

These metrics are commonly evaluated together when monitoring wholesale voice routes.

What Is a Good ACD?

There is no universal “good” ACD for every VoIP destination.

ACD varies according to:

• Destination country
• Mobile vs. fixed-line traffic
• Customer type
• Call-center traffic
• Business calling patterns
• Calling hours
• Traffic source
• Destination network
• Type of service

A five-minute ACD might be normal for one type of traffic but unusual for another.

Carriers should therefore compare ACD against historical traffic and similar routes, rather than applying one global benchmark.

ACD and Wholesale Route Quality

ACD can be useful when comparing multiple termination routes.

For example:

Route C has substantially lower ASR and ACD and higher PDD.

This combination may justify further investigation into the route, although the carrier should also consider the type and source of the traffic before concluding that the route itself is responsible.

Very Low ACD and Artificial Traffic

ACD can also be an important indicator when investigating traffic anomalies and telecom fraud.

For example, a sudden increase in large volumes of very short answered calls could warrant investigation.

Possible explanations include:

• Artificial traffic
• Traffic pumping
• Fraudulent activity
• Poor-quality dialing lists
• Aggressive automated dialing
• Destination-specific behavior
• Legitimate short-duration applications

ACD should not be used alone to classify traffic as fraudulent. Carriers should examine other indicators such as call patterns, destinations, SIP responses, CLI behavior, time-of-day distribution, ASR, CPS, and customer activity.

ACD in Call Centers

Call centers frequently monitor ACD because it provides insight into agent conversations and traffic behavior.

For example:

High ACD may indicate longer customer conversations.

Low ACD may indicate short interactions, unsuccessful conversations, automated calls, or rapid call termination.

However, the appropriate ACD depends heavily on the call center’s business model.

A customer-support center may naturally have a much higher ACD than a campaign conducting short outbound notifications.

ACD and Billing

ACD can also have commercial significance for wholesale carriers.

If a carrier terminates traffic on a per-minute basis, total call duration directly affects the number of billable minutes.

For example:

100,000 answered calls × 3 minutes average duration = 300,000 minutes

A change in ACD can therefore significantly affect traffic volume, revenue, and termination costs.

How Can Carriers Monitor ACD?

Wholesale carriers can monitor ACD through their softswitch, SBC, billing platform, CDR system, or VoIP management platform.

Useful analysis includes:

• ACD by destination
• ACD by customer
• ACD by route
• ACD by supplier
• ACD by CLI
• ACD by time period
• ACD by traffic type

Monitoring these values over time can help identify route degradation or unusual traffic patterns.

Common ACD Questions

What does ACD stand for in VoIP?

ACD commonly stands for Average Call Duration.

How is ACD calculated?

ACD = Total Duration of Answered Calls ÷ Number of Answered Calls

Is a higher ACD always better?

No. A higher ACD is not automatically better. The appropriate value depends on the destination and type of traffic.

What is the difference between ACD and ASR?

ASR measures how many call attempts are answered. ACD measures how long answered calls last on average.

Can ACD indicate fraud?

An unusual ACD pattern can be a fraud or traffic-quality indicator, but ACD alone cannot prove that traffic is fraudulent.

Why does ACD matter to wholesale carriers?

ACD helps carriers understand traffic behavior, evaluate route performance, identify anomalies, and estimate the commercial impact of different traffic patterns.

ACD Best Practices for Wholesale Carriers

Carriers should monitor ACD together with other key voice metrics rather than using it as a standalone quality indicator.

A practical route-performance view is:

ASR + ACD + PDD + CPS + CLI + Capacity + Call Quality

Comparing these metrics by destination, customer, supplier, and time period gives carriers a much clearer picture of actual route and traffic performance.