Understanding the impacts of short-term dynamics on long-term fairness of competing high speed TCP flows: A root-cause analysis

The short-term dynamics of competing high speed TCP flows can have strong impacts on their long-term fairness. This leads to severe problems for both the co-existence and the deployment feasibility of different proposals for the next generation networks. However, to our best knowledge, no root-cause analysis of the observation is available. In this paper, we try to fill this gap by providing an in-depth root-cause analysis of this phenomenon. We demonstrate that the widely used Jain´s index as a fairness metric can not provide sufficient characterization of the phenomena. More precisely, Jain´s index does not reflect the dynamic flow behaviors, e.g., starting time of the flows. We provide an analytical and simulation study to show the importance of the flow dynamics on fairness. We also propose a new metric called saturation time for fairness characterization. Both AIMD-based (HighSpeed TCP, BIC TCP) and MIMD-based (Scalable TCP) TCP versions are investigated in different topologies, namely dumb-bell and parking-lot topologies. In extreme cases, we also analyze and explain the “starving” effect of competing high speed TCP flows, when a flow forces other flows to deviate from their proper operation.