A CDR in VoIP is a call detail record, and CDRs are the most reliable way to monitor a VoIP route: they log every attempt with its timing, duration and release cause. Aggregate them per route and destination at least hourly, track ASR, NER, ACD, PDD and short calls, and alert on sudden changes rather than fixed levels.
Fields your CDRs need
Monitoring is only as good as the data. Make sure your switch writes these fields for every attempt, including failed ones:
| Field | Used for |
|---|---|
| Start time, ring time, answer time, end time | PDD, duration, hour of day analysis |
| Calling and called number (E.164) | Destination, breakout, fraud checks |
| Customer and supplier route (trunk) | Splitting statistics per carrier |
| SIP response code and Q.850 cause | NER, failure analysis |
| Who released the call | Dropped calls versus normal hang up |
| Codec and media IPs | Audio troubleshooting |
| Billed duration and rate | Cost and reconciliation |
Store numbers in a consistent format so that destinations map cleanly to your rate deck codes; see E.164 number format.
The metrics to track
- ASR and NER: answered calls and network completed calls as a share of attempts. Reading both is explained in NER vs ASR.
- ACD: average duration of answered calls. A drop often means bad audio or dropped calls.
- PDD: average and 90th percentile setup time.
- SDC: share of answered calls under your short call threshold, see short duration calls.
- Failure causes: the top SIP codes per route. A rise in 503 or 502 points to the carrier; a rise in 404 or 484 points to your number data.
- Volume and cost: attempts, minutes and spend per destination per hour.
How to aggregate
Always split by supplier route and destination (ideally down to the breakout, for example mobile operator), and by customer if you resell. A blended number for "Nigeria" can look fine while one operator fails completely. Use enough attempts before reacting: a few dozen calls give noisy percentages, so set a minimum sample (for example 50 or 100 attempts) before an alert fires.
Compare each route with its own recent history (same hour yesterday, same weekday last week) and with other routes carrying the same traffic. Absolute targets differ by destination and traffic type, so changes are a better trigger than fixed thresholds.
Alerts worth setting
- ASR or NER falls by a large share against the previous days on the same route.
- ACD drops sharply while ASR stays the same or rises (possible false answer or audio problems, see FAS).
- A single failure code suddenly dominates.
- Spend or minutes to a destination exceed a set level within an hour, especially at night or to high cost ranges. This is your first line of defence against revenue share fraud and toll fraud.
- Traffic appears to destinations a customer has never called before.
From monitoring to action
When an alert fires, check a sample of SIP traces, place test calls, and if the route is at fault, shift traffic to an alternative while you raise a ticket with clear examples: call times, numbers, codes. Keep the aggregated reports: they are also your evidence at the end of the month, when you reconcile your CDRs with the carrier's invoice as described in billing disputes and CDR reconciliation.
If your monitoring shows a destination with no reliable route, VoIPMatcher can source wholesale VoIP termination for it from its carriers. Request a VoIP route.
Frequently asked questions
What does CDR stand for in telecom?
CDR stands for call detail record: a log entry a switch writes for each call attempt, with the calling and called numbers, start, answer and end times, duration, the route used and the release cause. Carriers use CDRs for billing, quality monitoring, fraud detection and reconciling invoices between partners.
What is CDR analysis in VoIP?
CDR analysis means aggregating call records to measure how routes, destinations and customers perform. Typical outputs are ASR, NER, ACD, PDD, the share of short calls and spend per hour, plus the top failure codes. Comparing each route with its own history reveals quality drops, blocked destinations and fraud patterns quickly.
Is there a standard CDR file format?
There is no single format used by everyone. Switches export CDRs as CSV files or database records with their own field names, and some use RADIUS accounting or vendor formats. What matters is that every attempt, including failures, is logged with consistent time zones, E.164 numbers, the route, the SIP or Q.850 cause and billed duration.
How long should CDRs be kept?
Keep them at least as long as your billing dispute window and any retention period set by law or by your licence, which varies by country. For monitoring, detailed records for recent months plus aggregated reports for longer periods usually give enough history to compare trends and support disputes.
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