@book { VoiceoverIPverndertdenTelekommunikationsmarkt,
    title = "Voice over IP verändert den Telekommunikationsmarkt",
    author = "Claudia {Steinwender}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832470050",
    url = "https://m.diplom.de/document/222315"
}