The present invention concerns a method for data transmission with assured quality of service, as well as a gateway program module (GWM) for it, a front-end facility program module (VVM) for it, a terminal program module (EM) for it, a gateway (UAG) for it, a front-end facility (INA) for it and a terminal (TERA) for it. According to the method, a terminal (TERA, TELA) requests from a gateway (UAG), connected to a data network (INT), a communication connection to a communication partner facility (TELB) with at least one predefined quality of service. The gateway (UAG) then requests from the data network (INT) the communication connection with the at least one predefined quality of service. The gateway (UAG) establishes the communication connection via the data network (INT) if the data network (INT) can provide at least the at least one predefined quality of service for the communication connection, or via a switched telecommunication network (PSTN), in particular, switching assured physical and/or logical communication connections, unless the data network (INT) can provide at least the at least one predefined quality of service for the communication connection.