How Roaming Agreements are made

I have tried to pen down the basic algorithm followed to set up a Roaming agreement

1. Analyze the travel patterns of customers to identify the potential region, country for Roaming services.

2. Consider the corporate customers travel plans and Mobile usage requests while being out of the home network.

3. Take into consideration the business decision to make your presence felt in the home market (e.g. highest number of roaming toe-ups, roaming services in all the countries of the world)

3. Decide the region, country and approach the operator for Roaming tie-up

4. Carry out necessary Network and Billing systems tests as per GSM Roaming Guidelines

5. Commercial Roaming services are offered once the Tests are successful.

Basically, before a customer used Roaming services, it has to be enabled. The same could be done normally by calling the customer support and at times via the operator’s portal.

Once the Roaming service is enabled, the same would reflect in the HLR (Home Location Register) profile of the customer. The real magic starts now.

As soon as the customer travels to a different network (VPLMN Visited Public Mobile Network), network with the strongest signal strength is selected by the Handset (Assuming that the network selection is Automatic). A series of handshaking signals are exchanged between the Handset and the VPMN. Once it is done, VPMN tries to contact the HPMN (Home Public Mobile Network). Assuming that the handshaking between the VPLMN, HPLMN is successful, the customer will now be able to enjoy all the basic Mobile services he/she would have used being in the HPLMN.

Now let us see what happens during the handshaking between HPLMN and VPLMN.

VPLMN actually contacts the HPLMN and checks if the customer is authentic, if so what the services he/she is eligible for. The HPLMN maintains all the information about a customer in a register called HLR. –add more details.

The VPLMN also makes a local copy of this HLR called VLR.  Each time customers try to use the mobile services, VLR is referenced by the VPLMN, and accordingly, the service is entertained. The question here now how would the VPLMN intimate the HPLMN about the usage made by the customer while roaming. As different operators have different BSS/OSS(Business Support Systems/Operation Support Systems), it is obvious that a single standardized protocol for exchanging roaming usage information between operators is needed. The same is called TAP in the case of GSM roaming. TAP stands for Transferred Account Procedures. GSM Association is constantly working on standardizing and updating the TAP version as new services are evolved. As of now, the latest version of TAP is 3.11.