Air transportation is an important factor for the economic growth of the European Union, however, the current system is already approaching its capacity limits. These limitations stem mainly from the current European air traffic control system. New concepts have been developed to overcome the limitations of the current system. However, these concepts require sophisticated data communication capabilities. It has thus been agreed that the aeronautical air-ground communications infrastructure has to evolve to provide the capacity and quality of service required to reform air transportation. EU and USA, representing the regions experiencing the most pressure to reform their existing air-ground communication infrastructure, initiated activities to jointly identify and assess candidates for future digital aeronautical communication systems. Two initiatives for the development of the L-band Digital Aeronautical Communication System (L-DACS) were started. This book presents the analysis, design, and evaluation of the user plane quality of service protocols of L-DACS 1.