Method for ascertaining a billing tariff for a data transfer

1. A method for ascertaining a billing tariff for billing for a packet switched data transfer, where a mobile communication terminal which is involved in the data transfer and has access rights for a data mobile radio network is situated in a visitor mobile radio network, comprising:

setting up a data link between a billing system, which performs billing for the data transfer, and a central subscriber register in the data mobile radio network;

using the data link to transfer an item of location information, relating to the current location of the communication terminal, to the billing system;

establishing, using the item of location information, that the communication terminal is situated in the visitor mobile radio network; and

determining a billing tariff associated with the visitor mobile radio network, wherein

the data link is used to transfer an identifier identifying the mobile communication terminal from the billing system to the central subscriber register, and

the central subscriber register transfers the item of location information to the billing system,

setup of a data tunnel, used for transferring the data, from the communication terminal to a network gateway node in the data mobile radio network involves the identifier being transferred from a switching center, which is temporarily associated with the communication terminal, in the visitor mobile radio network to the network gateway node in the data mobile radio network,

the identifier is transferred from the network gateway node to the billing system,

the network gateway node transfers the identifier to an authentication server in the data mobile radio network using an authentication message, and

the authentication message is taken as a basis for transferring the identifier to a service computer gateway.

2. The method as claimed in claim 1 , wherein the identifier is transferred from the billing system to the central subscriber register at the start of the data transfer, and

the billing system stores the subsequently transferred item of location information for the duration of the data transfer.

3. The method as claimed in claim 1 , wherein a change in the current location of the communication terminal prompts the central subscriber register to transfer the item of location information automatically to the billing system.

4. The method as claimed in claim 3 , wherein the item of location information is stored in the billing system until the central subscriber register transfers an updated item of location information to the billing system.

5. The method as claimed in claim 1 , wherein

the method is initiated by the visitor mobile radio network receiving a request message from the communication terminal which relates to the data transfer,

a request is sent from the visitor mobile radio network to the central data store regarding that data mobile radio network for which the communication terminal has access rights, and

the data tunnel is set up to the network gateway node in the data mobile radio network.

6. The method as claimed in claim 1 , wherein

the network gateway node transfers the identifier to the authentication server via the service computer gateway,

the transfer involves the service computer gateway reading the identifier from the authentication message, and

the identifier is stored in the service computer gateway.

7. The method as claimed in claim 1 , wherein

the service computer gateway monitors the data transfer, and

monitoring information ascertained by the service computer gateway and the identifier are transferred to the billing system.

8. The method as claimed in claim 1 , wherein

the network gateway node receives a user name and/or a password from the communication terminal, and

the authentication message is transferred to the authentication server, the authentication message including the user name and/or the password.

9. The method as claimed in claim 8 , wherein the network gateway node receives from the communication terminal a user name which serves as a dummy and/or a password which serves as a dummy.

10. The method as claimed in claim 1 , wherein the data mobile radio network used is the home mobile radio network of the communication terminal.

11. The method as claimed in claim 1 , wherein

the billing system compares the item of location information with stored location information associated with various visitor mobile radio networks, and

a match between the item of location information and one of the stored items of location information prompts the billing system to establish that the communication terminal is situated in the associated visitor mobile radio network.

12. The method as claimed in claim 1 , wherein the item of location information transferred to the network gateway node is a visitor location register address, with the visitor location register address identifying a visitor location register, which is temporarily associated with the communication terminal, in the visitor mobile radio network.

13. The method as claimed in claim 1 , wherein a switching center which is temporarily associated with the communication terminal additionally transfers a parameter for the data transfer to the billing system, and the parameter is used when ascertaining the billing tariff.

14. The method as claimed in claim 13 , wherein the parameter for the data transfer which is transferred to the billing system is a bandwidth parameter for the air interface of the communication terminal.

15. The method as claimed in claim 1 , wherein the billing system used is a service control point in an intelligent network.

16. The method as claimed in claim 1 , wherein the data link is used to transfer to the billing system the item of location information which relates to the current location of the communication terminal using the message AnyTimeInterrogationResult.

17. The method as claimed in claim 1 , wherein the data link is used to transfer the identifier from the billing system to the central subscriber register using the message AnyTimeInterrogation.