The Tor network estimates its relays’ bandwidths using relay self-measurements of client traffic speeds. These estimates largely determine how existing traffic load is balanced across relays, and they are used to evaluate the network’s capacity to handle future traffic load increases. Thus, their accuracy is important to optimize Tor’s performance and strategize for growth. However, their accuracy has never been measured. We investigate the accuracy of Tor’s capacity estimation with an analysis of public network data and an active experiment run over the entire live network. Our results suggest that the bandwidth estimates underestimate the total network capacity by at least 50% and that the errors are larger for high-bandwidth and low-uptime relays. Our work suggests that improving Tor’s bandwidth measurement system could improve the network’s performance and better inform plans to handle future growth.
@inproceedings{torbwest-pam2021,
title = {On the Accuracy of Tor Bandwidth Estimation},
author = {Jansen, Rob and Johnson, Aaron},
booktitle = {Passive and Active Measurement Conference},
year = {2021},
doi = {10.1007/978-3-030-72582-2_28},
}