Since the seminal work by Kelly and co-workers, fluid flow models have been extensively used to model the traffic flow. This type of model have, e.g., been the basis for analysis of network stability and the development of new TCP clones. However, validation of fluid flow models has been quite limited. In this talk, we give an overview of the field and highlight some recent developments of a new fluid flow model that seems able to capture many of the characteristics that window based congestion control
exhibits.