A low-cost VoIP route can look attractive on a rate sheet but its real value depends on whether calls connect successfully and conversations last as expected. For wholesale VoIP providers these two factors make Answer-Seizure Ratio (ASR) and Average Call Duration (ACD) essential metrics for evaluating route quality.
ASR and ACD help telecom operators understand call completion patterns and identify changes that may require investigation. When interpreted together with call detail records and other performance indicators they support better routing decisions stronger carrier management and more informed cost control.
What Are ASR and ACD in VoIP?
Understanding Answer-Seizure Ratio
ASR measures the percentage of eligible call attempts that result in an answered call. The exact calculation depends on how the platform defines an attempt and which call outcomes it includes.
A common formula is:
ASR = Answered Call Attempts ÷ Total Eligible Call Attempts × 100
For example if a route handles 1,000 eligible call attempts and 650 result in answers its ASR is 65%.
A higher ASR can indicate better call completion performance but it does not automatically prove that a route delivers superior quality. Results can vary by destination calling patterns time of day and traffic mix.
Understanding Average Call Duration
ACD measures the average duration of connected calls over a defined reporting period. In many telecom reports it is calculated by dividing the total connected call duration by the number of answered calls.
For example if 500 answered calls generate 2,000 connected minutes the ACD is four minutes.
A consistent ACD can help operators understand typical calling patterns. A sudden decline may justify an investigation into call drops routing changes or changes in customer behavior.
The key distinction: ASR helps explain how often calls connect while ACD shows how long connected calls typically last.
Why ASR and ACD Matter for Route Quality
Measuring More Than the Price Per Minute
In wholesale VoIP termination a route's commercial value depends on more than its advertised rate. Operators must consider whether calls connect reliably and whether the resulting conversations meet customer expectations.
ASR and ACD help provide that perspective.
A route with a competitive rate but consistently poor call completion may generate customer complaints and lost revenue. Another route with a slightly higher rate may deliver better results and prove more valuable over time.
Example: Comparing Two Routes
Imagine a provider comparing two routes to the same destination:
Route A: ASR of 70% and ACD of 3.5 minutes.
Route B: ASR of 55% and ACD of 1.8 minutes.
Route A has stronger measured call completion and longer average connected calls in this example. However these figures alone do not establish why the routes differ or prove that Route A will perform better for every customer.
The operator should also examine call outcomes, traffic volume, time periods and the mix of calling numbers before changing the routing policy.
What High and Low ASR and ACD Can Reveal
Interpreting ASR Patterns
A high ASR can indicate that a large proportion of eligible call attempts are answered. A declining ASR may point to destination issues, carrier performance changes or a shift in the type of traffic being sent.
Possible causes include:
Incorrect number formatting or routing configuration
Destination numbers that are unavailable or unanswered
Carrier congestion or signaling failures
Changes in calling patterns
Filtering or rejection by downstream networks
A low ASR does not automatically mean the carrier is underperforming. For example a campaign calling unfamiliar recipients may naturally produce more unanswered calls than calls to established business contacts.
Interpreting ACD Patterns
ACD helps operators identify changes in the duration of connected calls. A sudden decline can indicate premature disconnections, routing changes or a different traffic mix.
A high ACD is not automatically a sign of superior quality either. Longer calls can reflect the purpose of the communication rather than network performance.
The practical rule: Investigate changes against the route's own historical baseline and compare equivalent destinations and traffic types before drawing conclusions.
How to Use ASR and ACD for Intelligent Routing
Moving Beyond Static Least-Cost Routing
Least-cost routing selects a route based on configured pricing and routing rules. While cost is important it does not always reflect call completion performance.
Dynamic routing can incorporate additional criteria such as ASR and ACD where supported by the switching platform.
DeNovoLab Class 4 Fusion documents routing strategies that include least-cost routing, highest-ASR routing and highest-ACD routing. Its routing engine also supports static strategies such as top-down, round-robin and percentage-based routing.
These options allow operators to build policies around their commercial and operational requirements rather than relying on a single routing criterion.
A Practical Routing Workflow
A provider might use the following process:
Compare ASR and ACD across eligible routes for the same destination.
Check rate differences and call failure reasons.
Identify routes that fall outside expected performance ranges.
Adjust routing priorities or failover rules where appropriate.
Monitor the results and reverse changes if performance deteriorates.
This creates a feedback loop between call performance and routing decisions.
It is important to avoid blindly optimizing for one metric. A route with the highest ASR may also be more expensive while a route with the highest ACD may reflect a different traffic mix. Routing policies should balance cost, quality and customer requirements.
ASR and ACD Reporting: What Should Your Softswitch Provide?
Essential Reporting Capabilities
Useful ASR and ACD reports should allow operators to filter results by destination, carrier, customer, trunk and time period where the platform supports those dimensions.
Reports should also provide enough context to explain the figures, including call attempts, answered calls, connected duration and failure outcomes.
Sippy, for example, documents ASR and ACD reporting alongside real-time monitoring for call-processing time, calls per second and concurrent calls. Its reporting tools also support customer and supplier CDR analysis.
DeNovoLab Class 4 Fusion combines switching, routing, billing, monitoring and reporting within an integrated telecom platform. Its documented routing capabilities include ASR-based and ACD-based dynamic routing.
When comparing platforms operators should assess the depth of reporting, calculation definitions, real-time visibility and integration with routing policies rather than judging software on the presence of a metric alone.
Why Reporting Accuracy Matters
Suppose one system calculates ASR using all call attempts while another excludes certain failure categories. Their percentages may differ even when they process the same traffic.
Consistent metric definitions are therefore essential for fair carrier comparisons and reliable routing decisions.
Best Practices for Improving Route Quality
Build a Repeatable Monitoring Process
ASR and ACD become more useful when they are part of a regular operational review rather than isolated numbers on a dashboard.
Follow these practices:
Set route-specific baselines: Compare performance with historical results for equivalent destinations.
Use sufficient sample sizes: Avoid major routing changes based on a handful of calls.
Review failure codes: Investigate why calls did not connect instead of relying on ASR alone.
Track trends over time: Compare hourly, daily and weekly patterns where relevant.
Evaluate cost alongside quality: Consider the commercial impact of routing changes.
Automate alerts carefully: Set thresholds that account for normal traffic variation.
Validate after changes: Confirm that a routing adjustment improves the intended outcome without creating new issues.
For example a route may experience a temporary ASR decline during a short traffic spike. An automatic switch to another carrier could be appropriate if the policy accounts for sufficient evidence and cost limits. A poorly designed rule may instead cause unnecessary route switching.
A measured approach helps prevent short-term fluctuations from driving costly operational decisions.
Conclusion: Make Better Routing Decisions With ASR and ACD
ASR and ACD provide two important perspectives on VoIP route performance. ASR helps operators understand call completion while ACD reveals the average duration of connected calls. Together with call detail records, failure analysis and cost data they help wholesale providers evaluate routes more effectively.
The objective is not simply to maximize both numbers. It is to identify reliable routes that meet customer expectations while maintaining commercially sustainable termination costs.
DeNovoLab Class 4 Fusion offers routing capabilities that include ASR-based and ACD-based dynamic routing alongside switching, billing and monitoring functions. These capabilities are worth evaluating for operators seeking a more integrated approach to route management.
Ready to improve visibility into your VoIP routing performance? Visit www.denovolab.com to explore Class 4 Fusion and assess how its routing and reporting capabilities can support your telecom operations.
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