Telecom Billing System Demystified

The phone calls we make, the SMS we send, the sites we browse are all billed by the telecom company based on the CDRs generated at the Switch.

A CDR is the source of information about the usage you made.

The CDRs generated by switch come to BSS generally through an intermediate system called Mediation.

People who are new in the Telecom space should visit this page and understand the basics of Mobile Technology first. The Mediation system takes various switch CDRs having their own native formats and converts them into a single format which is understood by the Billing System.

The CDR format depends upon the manufacturer of the Switch. At times the CDRs are encoded using ASN.1, at times in manufacture's own binary format. Apart from the CDRs, the Billing system also takes TAPIN files as input as shown in Fig 1.1.

In some systems, the TAPIN files may be sent to Mediation and in-turn Mediation sends it to the Billing System along with the CDRs. The Mediation system after decoding the CDRs, segregates the CDRs, and applies business filters, performs validation. The formatted, validated and most of the times filtered CDRs are then transferred to the Billing system.

The billing system in turn, reads the basic information of customers like Calling number, called number, IMSI, Call time, Type of call(Voice, SMS, GPRS etc)and based on these details identifies the rate plan to be applied.

Once rate plan is identified, the task left is to use the pricing unit (seconds rating for voice, bytes rating for GPRS) to be applied and calculate the price of the call. The output of the Billing System is in general a Bill or input to Bill generation or Invoicing system.

The billing system at times is linked to the Accounting System(e.g. Oracle Financials) also. Apart from the Bill, there is one more output of the Billing system and it is the TAP file. The TAP(Transferred Account procedures) file contains the data of the roaming customers.

For more information on Roaming, TAP files, click here. You could also visit the official page of GSM World . 

The below diagram shows a very high-level detail of various inputs to and outputs from a Billing System.