Traffic differentiation---giving better (or worse) performance to certain classes of Internet traffic---is a well-known but poorly understood traffic management policy. There is active discussion on whether and how ISPs should be allowed to differentiate Internet traffic, but little data about current practices to inform this discussion. Previous work attempted to address this problem for fixed line networks; however, there is currently no solution that works in the more challenging mobile environment.

The goal of this research is to detect traffic differentiation in cellular data networks. We define service differentiation as any attempt to change the performance of network traffic traversing an ISP's boundaries. ISPs may implement differentiation policies for a number of reasons, including load balancing, bandwidth management, or business reasons. Specifically, we focus on detecting whether certain types of network traffic receive better (or worse) performance. As an example, a wireless provider might limit the performance of third-party VoIP or video calling services (or any other competing services) by introducing delays or reducing transfer rates to encourage users to use services provided by the wireless provider. Previous work explored this problem in limited environments. Glasnost focused on BitTorrent in the desktop/laptop environment, and lacked the ability to conduct controlled experiments to provide strong evidence of differentiation. NetDiff covered a wide range of passively gathered traffic from a large ISP but likewise did not support targeted, controlled experiments. We address these limitations with Mobile Replay.