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Call Detail Records [CDR]

A Telecom Call Detail Record [CDR] or Station Message Detail Recording [SMDR] is a file containing information about recent system usage.

A Call Detail Record contains at a minimum the following fields:

  • Number making the call (A number) - Source ID - points of origin
  • Number receiving the call (B number) - Destination ID - endpoints
  • Date and Time call was commenced
  • Duration of the call
  • Amount billed for each call
  • Total usage time in the billing period
  • Total free time remaining in the billing period
  • Running total charged during the billing period.

Other information available:

  • Telephone exchange ID writing the record
  • Sequence number identifying the record
  • Additional digits on the B number used to correctly route or charge the call
  • Result of the call [answered, busy, failed to connect]
  • Route the call entered the exchange
  • Route the call left the exchange
  • Any fault condition encountered
  • Any facilities used during the call [call waiting, call diversion etc]

The format of the CDR varies among telecom providers or programs. A CDR file may contain more than one type of call traffic, with each type identified separately for rating purposes.

Many Telecom providers supply users with itemized bills, based on this CDR data.

CDRs are also used to analyse network performance, providing information on faulty calls and the amount of traffic along particular routes.

IP Detail Record [IPDR]

And IPDR provides data on Internet Protocol (IP)-based service usage and other activities as required by the Operational Support Systems [OSS] and Business Support Systems [BSS].

The content varies based on the service and the network. The envelope carrying the content must meet packaging, encoding and transport protocols specified by the Internet Protocol Detail Record Organization, Inc. []. aims to standardize usage information exchange between network and OSS/BSS systems. More on IPDR


While CDR and SMDR are similar, they are used by different groups, for different purposes:

  • CDR - used by Telco to create bill, charge for interconnect and roaming and manage the network performance.
  • SMDR - used by an end user organization to better understand their telephone usage and billing.



Generation of CDRs

CDRs are generated by Automatic Message Accounting [AMA] and processed by the Operations Support System [OSS].

Operations Support System [OSS]

An operational support system [OSS] is a set of programs used by a telecommunications service provider to monitor, control, analyze and manage a telephone or computer network.

With the complexities of merging call records of traditional voice telephone with packet-oriented Internet traffic [including VoIP], broadband applications such as teleconferencing and DSL, a more sophisticated systems was required to manage associated services such as:

  • Ordering and tracking network components [including IP addresses]
  • Usage and traffic patterns
  • Billing
  • Reporting

Tier 1 carriers generate billions of call detail records every day. With increasing pressure to complying with law enforcement to investigate call pattern analysis and manage revenue assurance, as well as standard operations such as better understanding network call routing patterns,

Call Accounting System

Telcos need powerful and sophisticated architecture to manage, store and analyse CDR's. CDRs are produced by the charging system of the telephone exchange. This is refered to as the Call Accounting System or Billing support system [BSS]. The billing system calculates the price of the call from the data in the CDR.

A Call Accounting System will collect, track and store data from calls of all types :

  • On-net, or internal calls which are routed from an extension on one switch to an extension on another switch.
  • On-net to off-net calls which are routed from an extension on one switch through another switch, and off to the public network.
  • Off-net to on-net calls which are routed from the inbound trunk of one switch to an extension on another switch.

Tandem Calls

  • All call records for each hop are stored as separate entries in the database.
  • All call records that represent a single call sequence are linked together. Each call is assigned up to two monetary values; the cost and the chargeback amounts.
  • Bill reconciliation reports present only one call for every call leaving or entering the network, showing the exact cost of the call.
  • Traffic Reports present all legs.
  • Chargeback reports present only the final leg, showing the chargeback amount. Note that the charge back amount may be equal to the cost or set to some different value. Also, on chargeback reports a call may have more than one final leg, such as in the case of call transfers/conference.

More on call accounting systems.

Communication Management Software

A system is also needed to transport the CDRs via computer networks to a central point for processing. This is known as Communication Management Software.

Next: IP Data Records [IPDR]

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