What is a telecom CDR file?

The CDR (Call Detail Record) file contains a set of data used to collect information on phone calls made or received during a specific period. This file, generally issued by the operator and/or PABX/PBX server, is mainly used in the telecommunications field to collect information on calls. Data collected can include metrics such as date, time, call duration, called or calling telephone number, call charges, etc.

The CDR file is usually issued in CSV (comma separated values) format, a file format commonly used to exchange data as spreadsheets. Thus, each row generally represents a call, and each column a call property of the call. The CDR file can be read using dedicated programs, such as Microsoft Excel or its open source equivalent OpenOffice, or any text editor : the CSV format is not encoded.

Use-cases example for CDR files

CDR files are commonly used in the telecoms industry to exchange information on communications, but this is not limited to calls. They can also be used for SMS, mobile data and other communication activities. Here are just a few examples of how CDR files are used:

CDR files for calls, the most common use, contain information such as call duration, called number, calling number, date and time of call, but also other relevant information, such as sometimes a customer code identifying the line with the provider, or an extension number in the case of CDRs from a PBX or SBC.

These files are generally used to bill customers for their phone calls, according to the package subscribed to the operator or reseller.


CDR files for SMS messages are similar to those for calls: they contain generic information such as the number of the recipient and sender, but also the number of characters contained in the message, as well as the date and time the message was sent, and a status as to whether the text message has been received.

Mobile data

CDR files for mobile data also contain information on the amount of data used, in bytes.

Using the CDR file

As we saw earlier, CDR files are essential for telecoms companies, enabling them to analyze, track and bill their customers’ use of communication services, on both land and mobile lines.

The collected data can be used to invoice the customer for calls, detect overtaxed calls and detect overages in a phone line subscription.

Telecom billing tools use these CDR files to value the cost of each call, according to the billing rules set by the reseller.

By reading the CDR file, you can also apply these rules to all communications over the month, in particular to detect when minutes allocated, mobile data usage or authorized destinations have been exceeded. In this way, each communication is evaluated in terms of overall usage over the month (or chosen period).

Last but not least, reading and processing CDR files allow us to create a call history and consumption file to be drawn up for the end customer, which are easier to understand than the raw CDR file transmitted by the line provider.

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