Reducing Congestion in the Tor Network with Circuit Switching

Abstract

The Tor network is a distributed circuit-switching overlay network, which provides anonymous communication by using voluntarily running onion routers around the world. Tor is vulnerable to network congestion and performance problems because circuit traffics with different rates are competing to transfer their data through a single TCP connection. A large fraction of available network capacity is consumed by the bulk users' traffic, resulting in increasing delays for the light interactive users. The unfair distribution between the circuit traffics of bulk and light users are contributing to bottleneck in the Tor routers. This problem increases the end-to-end latency and reduces the quality of communication in Tor, which discourages many users from using and joining the network. As a result, the degradation of Tor performance does not only affect the users' experience, but also degrade the anonymity of Tor. In this work, we discovered that the current Tor design encountered problems from several performance and deployment issues relating to lower network capacity. To improve the problems in Tor, we applied the circuit switching method and addressed the short-comings of limited network capacity, by connecting the congested OR to higher bandwidth ORs. The proposed method is evaluated on our setup testbed environment and partly in the live Tor network. The experimental results showed that TCP socket buffers and Tor network capacity are better utilized and the overall end-to-end latency is reduced.