Call Detail Record - CDR

Telecom billing process comprises provisioning the services within the billing system. like importing the CDRs from various sources and then calculation of rates, billing and at last the invoice generation.
In brief Telecom billing is the process of gathering and grouping telecommunication service for specific accounts or customers, producing and sending invoices, and keeping records of payments made to customer accounts. CDR is the basic unit of Telecom billing process.

Call Detail Record - CDR
A Call Detail Record (also known as Call Data Record - CDR) is the computer record produced by a telephone exchange containing details of a call that passed through it.
It comprises detailed information about the calls originating from, terminating at or passing through the exchange.
The embedded information in a CDR or Station Message Detail Recording (SMDR) is as follows:

The duration of each call
The amount billed for each call
The total usage time in the billing period
The total free time remaining in the billing period
The total charges during the billing period
The number making the call (calling party)
The number receiving the call (called party)
When the call started (date and time)
How long the call was (duration)
The number charged for the call
The identifier of the telephone exchange writing the record
A sequence number identifying the record
Additional digits on the called number used to 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
Call type (voice, SMS, etc)
Any fault condition encountered

The format of the CDR varies among telecom providers. A CDR for a particular account can be downloaded at the request of the subscriber who holds that account. If the telecom provider supplies users with itemized bills, a CDR will show up in each bill. The CDRs are generated by Automatic Message Accounting (AMA) and processed by the operations support system (OSS).
A CDR File may contain more than one type of call traffic. For example, fixed line voice traffic and fixed line data traffic may be placed in the same file, but will be identified separately for rating purposes.
A Call accounting software or communication management software is generally used to retrieve and process the CDR data

CDRs are produced by the charging system of the telephone exchanges. Generally, CDRs are created at the end of a call but on some phone systems the data is available during the call. This data is output from the phone system by a serial link known as the Station Message Detail Recording port (SMDR). Some of the details included in call records are: Time, Date, Call Duration, Number dialed, Caller ID information, Extension, Line/trunk location, Cost, Call completion status.
Call detail records, both local and long distance, can be used for usage verification, billing reconciliation, network management and to monitor telephone usage to determine volume of phone usage, as well as abuse of your company's telephone system. CDR's are an asset in managing long distance telephone costs and aid in the planning for future telecommunications needs. Besides for billing, CDRs can be used for supporting the operations of the telephone company by providing information about faulty calls and amount of traffic taken along particular routes.

The other benefits of CDR are as follows:

Control telecommunications costs with CDR analysis
Verify costs and usage
Resolve discrepancies with vendors
Disconnect unused service
Terminate leases on unused equipment
Deter or detect toll fraud of long distance services
Negotiate the most cost-effective call routing


Transport
Computer networks are used for transporting CDRs to a central point for processing, with X.25 links being widely used worldwide. The CDRs of calls still in progress are held by the sending exchange until the call is completed.

Call record (CDR) buffers
Call records are transmitted via serial port to a buffer, where they are temporarily stored until retrieved by call accounting software. It is a safe method transferring information to a call accounting or tele-management system.

SMDR (Station Messaging Detail Record)
While CDR and SMDR are similar, the most important difference is 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

CDR Processing (alias Mediation)
When the CDRs have been collected they must be checked (validation), reformatted (normalization) and consolidated for further processing.
The combined process of collection, validation, normalization and consolidation is also referred as mediation. This can be a very complex process.
Rating and Billing
Once CDRs have been collected, validated, normalized and consolidated, a charge is calculated for each call identified by the details in one or more CDRs. This process is known as rating and carried out by a rating engine. The rating engine can be part of a billing system or it can be a preliminary process outside of the billing system. In any event, the billing system adds up the charges determined during rating for each account, calculate balances and generate invoices. The CDRs then finally end up on the invoice in form of an itemized bill