Abstract: According to the invention, connection data (port-id) representing at least one subscriber's connection located in at least one communication network are transmitted to the at least one communication network. The transmitted connection data are used to authenticate the data transmitted via the at least one subscriber's connection. Preferably, additional connection data representing the subscriber's connection are available in addition to the subscriber-related data (user name and password) that are usually available for the authentication or authorization of the subscriber initiating a communication link via the communication network, thereby improving integrity of data transmission.