Call Detail Record (CDR)
How a call detail record works
A calling platform writes a call detail record when a call ends, one record for each call leg. A call leg is the connection between two endpoints. A call transferred from reception to a colleague has at least two legs, and therefore at least two records. The platform stores the records and makes them available for collection, by file transfer on on-premises systems and by API on cloud platforms. Billing systems and analytics software read them from there.
The exact fields depend on the platform, but most call detail records contain the same core set:
- Calling and called number: the extension or external number on each side of the leg.
- Start, answer and end time: when the call was placed, when it was answered, and when it ended. An unanswered call has no answer time.
- Duration: the connected time, from answer to end.
- Termination cause: the code that records how the call ended, such as a normal hang-up, a busy line, no answer, or a network failure.
- Device and trunk: the phone used and the external line the call went through.
- Call ID: the identifier that links the records belonging to the same call.
CDR vs call recording: what is the difference?
A call detail record describes a call, while a call recording captures what was said on it.
A call recording is an audio file of the conversation. A call recording exists only on lines where recording is enabled, and it is the source for transcripts, conversation analytics and quality reviews.
A call detail record is written for every call, recorded or not. A CDR contains no audio and no words, only the facts around the conversation: the numbers, the times, the duration, and how the call ended.
The difference shows when a customer complains. Suppose a customer says an agent hung up on them yesterday at 4 pm. The CDR confirms the call took place, shows that it lasted 40 seconds, and records how it ended. Only the recording shows what was said in those 40 seconds. A company with CDRs alone can prove the call happened. A company with recordings alone has to find the right file without the time, the number and the duration that the CDR provides.
What a call detail record is used for
Call detail records are used to answer questions about calls. The uses split into two groups, by one question: is the question about a single call, or about many calls together?
Questions about a single call
- Tracing a failed or dropped call: the termination cause and the trunk show where and why the call ended.
- Following a transferred call: linked legs show each step, from the first answer to the point where the call was lost.
- Verifying a disputed call: the record confirms whether a call happened, when, and for how long, for example when a carrier charge or a customer complaint is contested.
Questions about many calls
- Cost allocation and invoice checks: records matched to tariffs show what each department spent, and whether the carrier invoice is correct.
- Trunk sizing: peak concurrent calls show how many external lines the organization actually needs.
- Missed calls and answer times: records grouped by department or site show which lines leave callers unanswered, and at what hour.
The second group is the field of business call analytics, which collects CDRs across the organization and turns them into reports.
What affects the quality of call detail records
The usefulness of call detail records depends on five conditions, each visible in a specific report.
Linked legs. A call transferred twice should appear as one call with three legs. When the records are not linked by a shared call ID, a report counts three separate calls and loses the point where the caller hung up. Linked records give a cradle-to-grave view: the full path of a call, from the first ring to the last hang-up.
Unanswered and failed calls. Records of calls that never connected are what show missed and failed calls. Depending on the platform and its settings, calls with zero duration may not be written at all, and a report built on those records undercounts missed calls.
Time reference. Some platforms write timestamps in UTC. Without conversion to the local time of each site, a branch office in another time zone appears to take its calls in the middle of the night.
Platform format. Each calling platform, and sometimes each version, writes different fields under different names. An organization running two platforms has to normalize the records before comparing them, or the same metric is counted two different ways.
Directory match. A CDR identifies numbers and extensions, not people or departments. To read records by team or cost center, each extension has to be matched to the company directory.
Where Imagicle fits
Imagicle Advanced Analytics collects call detail records from Cisco UCM, Webex Calling, Microsoft Teams and contact centers, and links them into a cradle-to-grave call history. Advanced Analytics matches each record to users, departments and cost centers, and provides 50+ pre-made reports that can be exported and scheduled by email. With AI, users edit dashboards and reshape reports in natural language, for example filtering last quarter’s report by region, switching the chart type, or adding a metric. AI-generated business insights point out notable patterns in the call data, and every AI feature can be enabled, limited or disabled at any time.