This book answers a question which came about while the author was work­ ing on his diploma thesis [1]: would it be better to ask for the available band­ width instead of probing the network (like TCP does)? The diploma thesis was concerned with long-distance musical interaction ("NetMusic"). This is a very peculiar application: only a small amount of bandwidth may be necessary, but timely delivery and reduced loss are very important. Back then, these require­ ments led to a thorough investigation of existing telecommunication network mechanisms, but a satisfactory answer to the question could not be found. Simply put, the answer is "yes" - this work describes a mechanism which indeed enables an application to "ask for the available bandwidth". This obvi­ ously does not only concern online musical collaboration any longer. Among others, the mechanism yields the following advantages over existing alterna­ tives: ? good throughput while maintaining close to zero loss and a small bottleneck queue length ? usefulness for streaming media applications due to a very smooth rate ? feasibility for satellite and wireless links ? high scalability Additionally, a reusable framework for future applications that need to "ask the network" for certain performance data was developed.