Evaluation of Differentiated Services using an Implementation under Linux

Current efforts to provide distinct levels of quality-of-service in the Internet are concentrated on the Differentiated Services (DS) approach. In order to investigate the gain for users of those differentiated services, early experiences with implementations with respect to real applications are needed. Simulation models are often not sufficient if a judgement of the behavior under realistic traffic scenarios is desired. Because implementing new functionality into dedicated router hardware is difficult and time-consuming, we focused on a software implementation for standard PC hardware. In this paper we present an implementation of Differentiated Services functions for a PC-based router running under the Linux operating system. Two per-hop forwarding behaviors for Assured Service and Premium Service were realized. Components for traffic conditioning such as traffic meter, token bucket, leaky bucket and traffic shaper were implemented as well as an efficient traffic classificator and queueing disciplines. We describe the design and implementation issues of these components, which were validated in detail by measurements. Evaluation of these measurements shows that the proposed forwarding behaviors work well for boundary and interior routers. But, it also becomes apparent that standard applications using short-lived TCP connections cannot always exploit the requested service completely whereas rate-controlled sending applications are able to take full advantage of it. Furthermore, it is planned to release the implementation to the public for research purposes.