a first computer comprising

a first storage unit in which program instructions can be stored,

a first processor which executes the stored program instructions, and

a signaling unit for implementing features of the data transfer service that interfaces with a private branch exchange,

wherein the first computer is configured to process one or more application programs subjecting the first processor to a variable processing load; and

an input device,

a second computer operatively connected to the first computer via a data transmission network, the second computer configured according to information entered into the input device of the first computer, the second computer comprising

a data processing unit that processes the data to be transferred or actually transferred within the scope of the data transfer service, wherein with the signaling unit and the data processing unit in respective first and second computers the second computer is operated substantially independently of the first computer, and

a second storage unit and a second processor for use of the data processing unit, wherein the second computer further comprises a transmitting/receiving unit which receives data over the data transmission network and/or transmits data into the data transmission network, wherein the data transmission network operates according to an internet protocol, wherein the data comprises voice data and/or video data, wherein a quality indication of the voice data and/or video data is substantially determined by the second computer and is substantially independent of the variable processing load to which the first processor is subjected to when processing said one or more application programs,

wherein the second computer is disposed between the first computer and a hub of the data transmission network, and wherein in an overload situation data sent to or received by the second computer has a priority over data sent to or received by the first computer.