Call detail record

Call detail record

A Call Detail Record (CDR) is the computer record produced by a telephone exchange containing details of a call that passed through it. It is the automated equivalent of the paper toll tickets that were written and timed by operators for long distance calls in a manual telephone exchange.


A Call Detail Record contains at a minimum the following fields:
* the number making the call (A number)
* the number receiving the call (B number)
* when the call started (date and time)
* how long the call was (duration)Other information not necessarily required for billing the call may be included such as:
* the identifier of the telephone exchange writing the record
* a sequence number identifying the record
* additional digits on the B number used to correctly route or charge the call
* the result of the call (whether it was answered, busy etc)
* the route by which the call entered the exchange
* the route by which the call left the exchange
* any fault condition encountered
* any facilities used during the call, such as call waiting or call diversion


CDRs are produced by the charging system of the telephone exchange. In a Nortel exchange the charging system is called Automatic Message Accounting.


Computer networks are used to transport CDRs to a central point for processing.


Call accounting software is generally used to retrieve and process CDR data. This system can be called a Billing Support System (BSS). In the billing system the price of the call will be calculated.

As well as being used for billing CDRs can be used to support the operations of the telephone company by providing information on faulty calls and measures of the amount of traffic taken along particular routes.

MDR (Station Messaging Detail Record)

While CDR and SMDR are similar, the most important difference are their users. CDRs are for telephone company use, and may carry information about the processing of a call. To create actual billable call records, it may be necessary to correlate several CDRs. CDRs may also have a role in internal financial transfers among phone companies

SMDR, in contrast, is intended for end user organization, and as a way to understand their telephone usage and billing.

ee also

* NSA call database
* Telecommunications data retention
* Pen register
* Call accounting
* Internet Protocol Detail Record

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