Difficulties in Estimating Available Bandwidth

Available bandwidth estimation is very important for network operators, users, and bandwidth-sensitive applications. In the last 15 years, a large number of techniques and software tools have been introduced to estimate the available bandwidth actively. Many of them were verified in simulation and over a limited number of Internet paths. However, none of them have been widely used because there is still great uncertainty in their accuracy over the Internet at large. Based on the analysis of 11 well-known tools and our own experience in developing one of them, we present a comprehensive analysis of the fundamental difficulties with most of the existing tools.