When a request is sent by a switching unit, relating to the use of at least one subset of a codec mode configuration for the establishment of a transcoder-free operation connection by a radio network controller, it is checked whether the at least one requested subset is supported by the radio network controller. If the at least one subset of at least one codec mode configuration is supported, a transcoder-free operation connection to the switching unit and to the communication terminal is established by the radio network controller. Furthermore, a message relating to the at least one subset of the codec mode configuration to be used is signalled from the radio network controller to the communication terminal for the transmission of data.