  The efficiency of flow-based networking mechanisms strongly depends on
traffic characteristics and should thus be assessed using accurate flow models.
For example, in the case of algorithms based on the distinction between
elephant and mice flows, it is extremely important to ensure realistic flows'
length and size distributions. Credible models or data are not available in
literature. Numerous works contain only plots roughly presenting empirical
distribution of selected flow parameters, without providing distribution
mixture models or any reusable numerical data. This paper aims to fill that gap
and provide reusable models of flow length and size derived from real traffic
traces. Traces were collected at the Internet-facing interface of the
university campus network and comprise four billion layer-4 flow (275 TB).
These models can be used to assess a variety of flow-oriented solutions under
the assumption of realistic conditions. Additionally, this paper provides a
tutorial on constructing network flow models from traffic traces. The proposed
methodology is universal and can be applied to traffic traces gathered in any
network. We also provide an open source software framework to analyze flow
traces and fit general mixture models to them.
