International roaming allows a subscriber to access services virtually anywhere in the world. The visited network obviously needs to charge foreign subscribers for access time, transport, and services. As the visited network is not in a position to directly bill the roamers, it invoices their home network for the service usage. The home network then charges its own subscribers for the services used while roaming in a foreign network, using standard retail billing mechanisms. Figure 11-1 shows the interoperator billing process in its simplest form. John, a subscriber from PLMN A, roams in PLMN B. PLMN B allows John to use the services and collects the usage data. PLMN B then sends invoices and detailed records for service usage to John’s home PLMN, i.e., PLMN A. PLMN A settles the invoices according to the roaming agreement. PLMN A also generates a retail bill and charges John for the usage while roaming in PLMN B.
The number of roaming partners spread over different continents makes the interoperator billing process quite challenging. Moreover, complexity is added by partners using different network element technologies with varying billing data formats and transport methodologies. With the introduction of data roaming with GPRS and 3G and associated new services, the billing and settlement among wireless service providers is even more complicated. Several international industry forums and standards bodies are working to simplify and standardize this process for wireless service providers. Two of the GSM Association working groups, i.e., Billing, Accounting, and Roaming Group (BARG) and Transfer Accounting Data Interchange Group (TADIG) have contributed significantly in terms of standards and charging and billing principles for wireless operators using GSM technologies.
Figure 11-1 Interoperator billing and settlement process.
The CDMA Development Group (CDG) has developed processes and specifications for wireless operators using CDMA technologies.
TAP (Transferred Account Procedure) is the file format defined by GSM MoU TADIG and is used by GSM operators to exchange billing information with partner networks. The information includes both the charges that each roamer has to pay for the service usage as well as the detailed information related to the services used.
CIBER (Cellular Intercarrier Billing Exchange Roamer) is a proprietary protocol and specification for the exchange of roaming billing information, for voice and data. The wireless service providers using AMPS-based technologies, such as analog AMPS, IS-136 TDMA, and IS-95 CDMA, use CIBER records.
