Abstract: Quality of Service (QoS) supporting network architectures, like the Differentiated Services architecture, require a certain agreement regarding service levels. Traffic characteristics like data rates will be part of such agreements and, thus, senders must take care to stay within the agreed limits. Traffic shaping is one important mechanism to avoid penalties in networks (dropped or delayed packets) due to violations of the agreement. This paper presents a new traffic shaper based on Class-Based QoS for Linux that aims at shaping aggregate traffic as well as individual flows within an aggregate. In comparison to other approaches (e.g., Class-Based Queuing), our Flow Based Queuing mechanism causes significantly less jitter. Implemented in end-systems, this approach even benefits from direct interaction with applications to create traffic in accordance to application requirements.