An Adaptive IP Telephony Application over Differentiated Services

This paper describes a concept based on application adaptivity and Differentiated Services (DiffServ) in order to provide the Quality-of-Service (QoS) required by realtime applications. Assuming the availability of different service classes, we propose that a real-time application always selects the lowest / cheapest service class that still can meet the application requirements. The selection depends on RTP-based QoS monitoring and on additional probing of the quality of the next lower service class. The service class selection algorithm has been implemented within an IP telephony application and evaluated in a test-bed consisting of Linux-PC based DiffServ routers. The evaluation proves the suitability of the approach but also shows several issues for further improvement.