VoIP Metrics — ASR, ACD, NER, PDD
VoIP quality monitoring relies on 4 key indicators. Understanding these metrics lets you optimize your infrastructure and identify problems before they affect your users.
ASR — Answer Seizure Ratio
Definition: Percentage of successful calls (200 OK response) out of total attempts.
Formula: ASR = (Answered calls / Total attempts) × 100
| Value | Interpretation |
|---|---|
| > 95% | Excellent — premium-quality trunk |
| 90 – 95% | Good — normal for international telephony |
| 80 – 90% | Average — check routes and destinations |
| < 80% | Problem — degraded trunk, action required |
A low ASR may indicate: invalid destinations, trunk overload, international routing problem.
ACD — Average Call Duration
Definition: Average duration of completed calls, in seconds.
Formula: ACD = Total call duration / Number of answered calls
- 180 – 300 s: Standard business
- > 600 s: Normal for contact centers
- < 30 s: Alert — hung-up calls, insufficient audio quality
A sudden drop in ACD on your account often signals an audio quality problem (echo, dropouts).
NER — Network Effectiveness Ratio
Definition: Measures network reliability by excluding voluntary abandonments.
Formula: NER = (Completed calls / Connected calls) × 100
- > 98%: Excellent
- 95 – 98%: Acceptable
- < 95%: Network stability problem
PDD — Post Dial Delay
Definition: Delay between the end of dialing and receipt of the 180 Ringing signal.
| PDD | Quality |
|---|---|
| < 2 s | Excellent |
| 2 – 5 s | Acceptable |
| > 5 s | Problem — network latency or trunk overload |
Where to view these metrics
In your WebTic client area → Monitor tab of your SIP Trunk service. Data is updated in real time. CDRs (Call Detail Records) are available from the CDR tab with filters by date, destination and duration.
Corrective actions
- Low ASR: Contact WebTic support with the failing destination numbers
- High PDD: Check network latency (
ping sip.webtic.online), change codec - Low ACD: Investigate audio quality — run a SIPp test, capture a pcap
