Exploring the Potential Benefits of Expanded Rate Limiting in Tor:
Slow and Steady Wins the Race With Tortoise
Brad Moore, Chris Wacek, and Micah Sherr
Tor is a volunteer-operated network of application-layer relays that enables users to communicate privately and anonymously. Unfortunately, Tor often exhibits poor performance due to congestion caused by the unbalanced ratio of clients to available relays, as well as a disproportionately high consumption of network capacity by a small fraction of filesharing users.
Tortoise argues the very counterintuitive notion that slowing down traffic on Tor will increase the bandwidth capacity of the network and consequently improve the experience of interactive web users. Tortoise is a system for rate limiting Tor at its ingress points. We demonstrate that the system incurs little penalty for interactive web users, while significantly decreasing the throughput for filesharers. Our techniques provide incentives to filesharers to configure their Tor clients to also relay traffic, which in turn improves the network’s overall performance. We have showen large-scale emulation results that indicate interactive users will achieve a significant speedup if even a small fraction of clients opt to run relays.
We built Tortoise on the Tor version 0.2.1.28. If you’re interested in trying out Tortoise for yourself, you can apply the patch below to Tor 0.2.1.28.