Method for operating a switching device using different signalling protocols, - in which a switching device conveys data in a telecommunications network, - between a control unit for controlling the switching device and a first terminal, a first protocol is used for signalling control commands, - the control unit is connected to a second terminal by means of an interface, - between the interface and the second terminal for signalling control commands, a second protocol is used which differs from the first protocol, - in which a conversion unit (50, 52) enclosed by the interface embeds control commands received from the control unit according to the first protocol into control commands according to the second protocol and sends them to the second terminal, - and / or from control commands received from the second terminal according to the second protocol, takes control commands according to the first protocol which have previously in the second terminal been embedded in signalling commands according to the second protocol, and sends them to the control unit, - in which a first voice transmission unit enclosed by the interface divides voice data transmitted in a voice channel into data packets, - in which a second voice transmission unit enclosed by the interface takes voice data from data packets and sends them in a voice channel, characterised in that - a coupling unit assigned to the first and second voice transmission unit and enclosed by the interface is connected to the conversion unit (50, 52), - in the conversion unit (50, 52) the control commands received according to the first signalling protocol are checked to determine whether a useful data connection needs to be established or terminated between the switching device and the second terminal, and - in the event of the occurrence of a sought command, the occurrence of the coupling unit is signalled, which triggers the establishment or termination of the useful data connection, wherein, if the useful data connection is established or terminated, the coupling unit and the second terminal exchange control commands according to a third functional protocol. - in which a switching device conveys data in a telecommunications network, - between a control unit for controlling the switching device and a first terminal, a first protocol is used for signalling control commands, - the control unit is connected to a second terminal by means of an interface, - between the interface and the second terminal for signalling control commands, a second protocol is used which differs from the first protocol, - in which a conversion unit (50, 52) enclosed by the interface embeds control commands received from the control unit according to the first protocol into control commands according to the second protocol and sends them to the second terminal, - and / or from control commands received from the second terminal according to the second protocol, takes control commands according to the first protocol which have previously in the second terminal been embedded in signalling commands according to the second protocol, and sends them to the control unit, - in which a first voice transmission unit enclosed by the interface divides voice data transmitted in a voice channel into data packets, - in which a second voice transmission unit enclosed by the interface takes voice data from data packets and sends them in a voice channel, characterised in that - a coupling unit assigned to the first and second voice transmission unit and enclosed by the interface is connected to the conversion unit (50, 52), - in the conversion unit (50, 52) the control commands received according to the first signalling protocol are checked to determine whether a useful data connection needs to be established or terminated between the switching device and the second terminal, and - in the event of the occurrence of a sought command, the occurrence of the coupling unit is signalled, which triggers the establishment or termination of the useful data connection,