what is a TAP file

Need of TAP files

While the customer is using the Roaming network, the usage CDRs are generated at Roaming networks switch but the customer is billed by the Home network. So there has to be some mechanism through which the Roaming network intimates the Home networks about its customer usage and in turn earn revenue for providing Roaming Services. The mechanism used by the GSM community is of TAP files. TAP stands for Transferred Account Procedures.

TAP File internals

TAP files are binary files encoded using ASN.1 BER encoding. In order to read/edit the TAP files, a special tool/editor is needed with the capabilities to understand and decode ASN.1 encoding.

As mentioned earlier, the TAP file is used as a medium to transfer user usage details among the Telecom operators, the TAP files consist of information like Calling party, called party, duration, type of service code, time of call, etc. So does it mean the TAP file is like the CDR files?

The answer is both YES and NO.

Yes, because it does have the usage information like the CDR files but No because of the following points

a. Unlike CDR files, TAP files have the applicable call charge, taxation details also

b. The format of the CDR file is MSC vendor dependent whereas the TAP files version is managed by GSM Association.

There are various versions of the TAP file and each version different has significance to it.

The first version of TAP file was 3.1 and the current version if 3.11

How currency is used for the charge, tax part in the TAP file?

The TAP files are generally generated by the Billing System. The Billing system could be made such that either it can represent charge in the Local currency of the Roaming network or the Local currency of the Home network of the customer. In both, the approaches, the billing system either at the Roaming network or at the Home network will have to maintain a database of currencies of its Roaming partner networks. This will not be feasible as the operators have to take care of the currency fluctuations and all.

There are various reasons which forced the TAP files to change

a. Reporting

b. Charging of new services

c. Security