Method for ascertaining a billing tariff for billing for a data transfer

1. A method for ascertaining a billing tariff for billing for a 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 tunnel, used for transferring the data, from the communication terminal to a network gateway node in the data mobile radio network prompting transfer of an item of location information which relates to the communication terminal from a switching center, temporarily associated with the communication terminal, in the visitor mobile radio network to the network gateway node in the data mobile radio network;

transferring the item of location information to a billing system;

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

ascertaining a billing tariff associated with the visitor mobile radio network, 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 the data mobile radio network for which the communication terminal has access rights,

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

the network gateway node transfers the item of location information 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 item of location information to a service computer gateway.

2. The method as claimed in claim 1 , wherein the network gateway node transfers the authentication message to the authentication server via the service computer gateway;

the transfer involves the service computer gateway reading the item of location information from the authentication message; and

the item of location information is stored in the service computer gateway.

3. The method as claimed in claim 1 , wherein the service computer gateway monitors the data transfer; and

monitoring information ascertained and the item of location information are transferred from the service computer gateway to the billing system.

4. 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 containing the user name and/or the password.

5. The method as claimed in claim 4 , wherein the network gateway node receives from the communication terminal a user name which serves merely as a dummy and/or a password which serves as a dummy.

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

7. 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.

8. The method as claimed in claim 1 , wherein the switching center transfers to the network gateway node, as an item of location information, a switching center address which identifies the switching center.

9. The method as claimed in claim 1 , wherein the switching center additionally transfers a parameter for the data transfer to the billing system, and the parameter is used when ascertaining the billing tariff.

10. The method as claimed in claim 9 , 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.