Method for the transmission of digital data over several data transmission networks, the associated units and associated program

The present invention relates to a system and method in which user data is initially transmitted to a first network gateway by means of a first data transmission network. The user data is encoded according to a first encoding type. The network gateway feeds the user data into a circuit-switching network without further code conversion. The original encoding type and a second encoding type, permissible in the circuit-switching network, are signaled to the circuit-switching network. The signaling of the first encoding type is transferred by the circuit-switching network to a further network gateway unprocessed. The user data is transmitted in the data transmission network as if encoded by means of the permissible encoding type.