On TCP performance in flow-based mix networks

Anonymity technologies such as mix networks have gained increasing attention as a way to provide communication privacy. Mix networks were developed for message based applications such as email, but researchers have adapted mix techniques to low-latency, flow-based applications such as anonymous web browsing. In this paper we systematically address TCP performance issues of flow-based mix networks. We explain why a mix's batching and reordering schemes can dramatically reduce TCP throughput due to out-of-order packet delivery. We developed a theoretical model to analyze such impact and present closed formulae for TCP throughput in mix networks. To improve TCP performance, we examined the approach of increasing TCPs duplicate threshold parameter and derived closed formulae for the performance gains. Our simulation results matched our theoretical analysis well.