Authentication method and system

The present invention relates to an authentication method and system for identifying a subscriber ( 1 ) of a first network an address of the second network ( 9 ) is allocated to the subscriber ( 1 ). An information about a mapping between the address of the second network ( 9 ) and a subscriber identity is generated and transmitted to the second network ( 9 ). Thereby, an authentication server connection is provided between the first network ( 2 ) and the second network ( 9 ), such that the subscriber identity can be handled over to the second network ( 9 ). Thus, a VAS platform of the second network ( 9 ) can receive the address of the second network and the subscriber identity of the subscriber ( 1 ), such that subscriber accessing services of the VAS platform can be identified for charging and/or addressing purposes.