Patent ID: 7292840

Claim:
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.