Thesis or Dissertation A Study on Performance Improvement of Tor Network with Active Circuit Switching

Timothy Girry, Kale  ,  Timothy Girry, Kale

pp.1 - 142 , 2015-09-30 , The University of Electro-Communications
Tor is an onion routing overlay network that provides anonymous communication in the public Internet, by routing the messages on random onion routers around the world. Tor experienced many performance problems such as network congestion because the circuits with different transferring rates are competing to transfer their data through a single TCP connection. Tor users who transfer larger traffic always consume larger bandwidth resources, which resulting in increasing delays for the light interactive users. The unfair distribution of light and bulk traffics makes the bottleneck in the Tor routers and degrades the quality of communication. This problem discourages many Tor users from joining the Tor network; as a result, the Tor performances and the anonymity services are significantly degrade. Firstly, we explored the occurrence of latency problems in Tor. Experiments were carried out to observe the details of latency by circuit traffic and computational latency. We observed that multiplexing circuits in a single OR causes the delays to increase in the Tor network. We measured the effects of multiplexing the light and bulk circuits to single TCP connection in a setup testbed environment and partly in the live Tor network. In our experiments, we observed that current Tor design encountered problems from several performance issues relating to lower network capacity, lower throughput and increasing queuing delays in Tor and TCP buffers. To solve these problems, we applied an active circuit switching approach to address the limitation of Tor network capacity. We implemented the circuit switching in the entry ORs, which monitors the occurrence of traffic congestion and construct the TCP connection to higher bandwidth ORs. We performed small modification in the current algorithm of Tor and implemented our control metrics to show our proposal has improved the multiplexing issues of buffer overflowing and socket un-writable events. We showed the design for the proposed method and the details of circuit switching procedures. Finally, the experimental results showed the distribution of circuit traffics between the light and bulk clients are improved, and the TCP socket buffers and network capacity are also improved. The end-to-end throughput is increased and the end-to-end latency is reduced compared to the default stock Tor.

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